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The state of the art to describe image quality in medical imaging is to assess the performance of an observer conducting a task of clinical interest. This can be done by using a model observer leading to a figure of merit such as the signal-to-noise ratio (SNR). Using the non-prewhitening (NPW) model observer, we objectively characterised the evolution of its figure of merit in various acquisition conditions. The NPW model observer usually requires the use of the modulation transfer function (MTF) as well as noise power spectra. However, although the computation of the MTF poses no problem when dealing with the traditional filtered back-projection (FBP) algorithm, this is not the case when using iterative reconstruction (IR) algorithms, such as adaptive statistical iterative reconstruction (ASIR) or model-based iterative reconstruction (MBIR). Given that the target transfer function (TTF) had already shown it could accurately express the system resolution even with non-linear algorithms, we decided to tune the NPW model observer, replacing the standard MTF by the TTF. It was estimated using a custom-made phantom containing cylindrical inserts surrounded by water. The contrast differences between the inserts and water were plotted for each acquisition condition. Then, mathematical transformations were performed leading to the TTF. As expected, the first results showed a dependency of the image contrast and noise levels on the TTF for both ASIR and MBIR. Moreover, FBP also proved to be dependent of the contrast and noise when using the lung kernel. Those results were then introduced in the NPW model observer. We observed an enhancement of SNR every time we switched from FBP to ASIR to MBIR. IR algorithms greatly improve image quality, especially in low-dose conditions. Based on our results, the use of MBIR could lead to further dose reduction in several clinical applications.

Introduction Crystal-related arthropathies are a growing global health problem and imaging plays an important role in the diagnosis. Indeed, distinguishing crystal type, whether monosodium urate or one of the calcium crystal types is a clinical challenge because diagnosis and treatment depends on the crystal type involved. Although clinical imaging has made substantial progress in recent years, particularly with the development of dual-energy CT (DECT) protocols in people with longstanding and/or tophaceous gout, the diagnostic performance of DECT remains limited in the early stages of gout4. Moreover, while DECT is relatively accurate in distinguishing monosodium urate (MSU) from the various calcium deposits, there is currently no imaging technique capable of noninvasively differentiating one calcium crystal type from another in crystal-related arthropathies, whether in or around the joints. We aimed to determine the in vitro diagnostic performance of multi-energy spectral photon-counting CT (SPCCT) in crystal-related arthropathies. Methods Four crystal types (monosodium urate, MSU; calcium pyrophosphate, CPP; octacalcium phosphate, OCP; and calcium hydroxyapatite, CHA) were synthesized and blended with agar at the following concentrations: 240, 88, 46, and 72 mg/mL, respectively. Crystal suspensions were scanned on a pre-clinical SPCCT system at 80 kVp using the following four energy thresholds: 20, 30, 40, and 50 keV. Differences in linear attenuation coefficients between the various crystal suspensions were compared using the receiver operating characteristic (ROC) paradigm. Areas under the ROC curves (AUC), sensitivities, specificities, and diagnostic accuracies were calculated. Crystal differentiation was considered successful if AUC > 0.95. Results Multi-energy SPCCT can accurately differentiate MSU from CPP and CHA, CPP from OCP, and OCP from CHA in vitro. The distinction between MSU and OCP, and CPP and CHA is more challenging. Conclusions Multi-energy SPCCT can accurately differentiate MSU from CPP and CHA, CPP from OCP, and OCP from CHA in vitro. The distinction between MSU and OCP, and CPP and CHA is more challenging. The accurate identification and characterization of MSU and various calcium crystals would help improve both diagnosis and management of crystal-related arthropathies.

Purpose Fluoroscopically-guided procedures are among the most irradiating medical interventions. Thus, a fair amount of pressure is put on reducing patient exposure. This can be achieved by adapting the unit’s protocols, and by using technical upgrades. However, it is important to check if any image information content is lost. To our knowledge, there is no existing metric able to objectively assess the detectability of moving structures in fluoroscopic images. This work proposes a new method to assess image quality for a clinically relevant detection task in dynamic conditions using a mathematical observer. Methods A thin PMMA plate, supporting a 0.014” guidewire, was attached to a motion simulation engine via a cantilever, allowing motion with velocities and amplitudes representative of coronary arteries. The guidewire was placed at the unit’s isocenter, while 20 cm of PMMA around it simulated a patient. Images were acquired using pre-defined fluoroscopy quality levels (low, medium, and high) on two different units: One dedicated for interventional cardiology (IC), (Philips AlluraClarity FD10) the other for a broader purpose range (Philips Veradius Neo). Regions of interest were extracted from the images, either in the homogenous zones (signal-absent), or along the guidewire (signal-present). A mathematical model observer computed a decision variable for each signal-absent and signal-present image. The signal-to-noise ratio (SNR) between both decision variable distributions was taken as the figure of merit of the guidewire detectability. Dose rates were measured at the entrance of the PMMA using a pencil ionisation chamber. Results Preliminary results show that, for the IC unit, the SNR is equal to 3.5, 4.1 and 4.9 for respectively low (reference dose rate), medium (×1.6 rate) and high (×3.7 rate) quality fluoroscopy settings. In comparison, the same measurement on the non IC-dedicated unit yields a SNR of only 2.0 (high quality setting), at a dose rate comparable (11.5 vs. 12.2 mGy min−1) to medium quality fluoroscopy on the IC unit. Conclusions We have shown the feasibility of using a model observer to assess the detectability of a moving coronary guidewire. Further developments will include the fine tuning of the model, and matching between human observer results.

OBJECTIVE: To compare image quality of a standard-dose (SD) and a low-dose (LD) cervical spine CT protocol using filtered back-projection (FBP) and iterative reconstruction (IR). MATERIALS AND METHODS: Forty patients investigated by cervical spine CT were prospectively randomised into two groups: SD (120 kVp, 275 mAs) and LD (120 kVp, 150 mAs), both applying automatic tube current modulation. Data were reconstructed using both FBP and sinogram-affirmed IR. Image noise, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were measured. Two radiologists independently and blindly assessed the following anatomical structures at C3-C4 and C6-C7 levels, using a four-point scale: intervertebral disc, content of neural foramina and dural sac, ligaments, soft tissues and vertebrae. They subsequently rated overall image quality using a ten-point scale. RESULTS: For both protocols and at each disc level, IR significantly decreased image noise and increased SNR and CNR, compared with FBP. SNR and CNR were statistically equivalent in LD-IR and SD-FBP protocols. Regardless of the dose and disc level, the qualitative scores with IR compared with FBP, and with LD-IR compared with SD-FBP, were significantly higher or not statistically different for intervertebral discs, neural foramina and ligaments, while significantly lower or not statistically different for soft tissues and vertebrae. The overall image quality scores were significantly higher with IR compared with FBP, and with LD-IR compared with SD-FBP. CONCLUSION: LD-IR cervical spine CT provides better image quality for intervertebral discs, neural foramina and ligaments, and worse image quality for soft tissues and vertebrae, compared with SD-FBP, while reducing radiation dose by approximately 40 %.

The goal of the present work was to report and investigate the performances of a new iterative reconstruction algorithm, using a model observer. For that, a dedicated low-contrast phantom containing different targets was scanned at four volume computed tomography dose index (CTDIvol) levels on a Siemens SOMATOM Force computed tomography (CT). The acquired images were reconstructed using the ADMIRE algorithm and were then assessed by three human observers who performed alternative forced choice experiments. Next, a channelised hotelling observer model was applied on the same set of images. The comparison between the two was performed using the percentage correct as a figure of merit. The results indicated a strong agreement between human and model observer as well as an improvement in the low-contrast detection when switching from an ADMIRE strength of 1–3. Good results were also observed even in situations where the target was hard to detect, suggesting that patient dose could be further reduced and optimised.

A version of cascaded systems analysis was developed specifically with the aim of studying quantum noise propagation in x-ray detectors. Signal and quantum noise propagation was then modelled in four types of x-ray detectors used for digital mammography: four flat panel systems, one computed radiography and one slot-scan silicon wafer based photon counting device. As required inputs to the model, the two dimensional (2D) modulation transfer function (MTF), noise power spectra (NPS) and detective quantum efficiency (DQE) were measured for six mammography systems that utilized these different detectors. A new method to reconstruct anisotropic 2D presampling MTF matrices from 1D radial MTFs measured along different angular directions across the detector is described; an image of a sharp, circular disc was used for this purpose. The effective pixel fill factor for the FP systems was determined from the axial 1D presampling MTFs measured with a square sharp edge along the two orthogonal directions of the pixel lattice. Expectation MTFs were then calculated by averaging the radial MTFs over all possible phases and the 2D EMTF formed with the same reconstruction technique used for the 2D presampling MTF. The quantum NPS was then established by noise decomposition from homogenous images acquired as a function of detector air kerma. This was further decomposed into the correlated and uncorrelated quantum components by fitting the radially averaged quantum NPS with the radially averaged EMTF(2). This whole procedure allowed a detailed analysis of the influence of aliasing, signal and noise decorrelation, x-ray capture efficiency and global secondary gain on NPS and detector DQE. The influence of noise statistics, pixel fill factor and additional electronic and fixed pattern noises on the DQE was also studied. The 2D cascaded model and decompositions performed on the acquired images also enlightened the observed quantum NPS and DQE anisotropy. journal_title: Physics in Medicine and Biology article_type: paper article_title: A comprehensive model for quantum noise characterization in digital mammography copyright_information: © 2016 Institute of Physics and Engineering in Medicine license_information: cc-by Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. date_received: 2015-10-06 date_accepted: 2016-01-05 date_epub: 2016-02-19 ispartof: Physics in Medicine and Biology vol:61 issue:5 pages:2083-108 ispartof: location:England status: published

Evaluating image quality by using receiver operating characteristic studies is time consuming and difficult to implement. This work assesses a new iterative algorithm using a channelised Hotelling observer (CHO). For this purpose, an anthropomorphic abdomen phantom with spheres of various sizes and contrasts was scanned at 3 volume computed tomography dose index (CTDIvol) levels on a GE Revolution CT. Images were reconstructed using the iterative reconstruction method adaptive statistical iterative reconstruction-V (ASIR-V) at ASIR-V 0, 50 and 70 % and assessed by applying a CHO with dense difference of Gaussian and internal noise. Both CHO and human observers (HO) were compared based on a four-alternative forced-choice experiment, using the percentage correct as a figure of merit. The results showed accordance between CHO and HO. Moreover, an improvement in the low-contrast detection was observed when switching from ASIR-V 0 to 50 %. The results underpin the finding that ASIR-V allows dose reduction.

The rapid increase in the number of computed tomography (CT) scans performed has augmented concerns about safety risks. Although some of this increase is certainly legitimate and improves patient care, there is certainly still a need for dose reduction. Patients may insist on receiving a CT scan, and defensive medicine can certainly be a source of useless exposure. This means that the principle of justifying CT examinations needs to be reemphasized. Dealing with a properly justified examination is then a matter of image optimization aimed at providing the necessary diagnostic information at the lowest possible applied dose. The optimization of CT acquisition protocols involves teamwork in which manufacturers, legal bodies, radiologists, technologists, and medical physicists all play an important role. The purpose of this article is to review the latest progress in terms of the optimization of CT acquisition protocols in the pediatric population.

The aim of this study was to investigate the radiation exposure of the Swiss population to interventional procedures. A nationwide survey was conducted in Switzerland. The annual effective dose per capita due to interventional procedures was found to be 0.14 mSv, corresponding to 12% of the total dose. Coronary angiography and percutaneous coronary interventions were found to be the most frequent and the most irradiating interventional procedures, accounting for 52% of the total examination frequency and 64% of the dose delivered to the population. Switzerland stands at the same level as other countries in terms of effective dose per capita due to interventional radiology.

Nationwide surveys on radiation dose to the population from medical radiology are recommended in order to follow the trends in population exposure and ensure radiation protection.The last survey in Switzerland was conducted in 1998,and the annual effective dose from medical radiology was estimated to be 1 mSv y j(-1) per capita. The purpose of this work was to follow the trends in diagnostic radiology between 1998 and 2008 in Switzerland and determine the contribution of different modalities and types of examinations to the collective effective dose from medical x-rays. For this reason, an online database(www.raddose.ch) was developed. All healthcare providers who hold a license to run an x-ray unit in the country were invited to participate in the survey. More than 225 examinations, covering eight radiological modalities, were included in the survey. The average effective dose for each examination was reassessed. Data from about 3,500 users were collected (42% response rate). The survey showed that the annual effective dose was 1.2 mSv/capita in 2008. The most frequent examinations are conventional and dental radiographies (88%). The contribution of computed tomography was only 6% in terms of examination frequency but 68% in terms of effective dose. The comparison with other countries showed that the effective dose per capita in Switzerland was in the same range as in other countries with similar healthcare systems, although the annual number of examinations performed in Switzerland was higher.

Introduction (1) To highlight the spread of patient exposure and image quality performances for various abdominal protocols. (2) To ensure that radiation dose reductions in abdominal CT protocols do not impair the detection of low-contrast structures. Methods An anthropomorphic abdominal phantom (QRM, Moehrendorf, Germany) with two optional rings (2.5 cm and 5 cm), representing the attenuation of an adult abdomen of 50 kg (small phantom), 75 kg (medium phantom) and 100 kg (large phantom), was scanned on 70 CT machines in the Western part of Switzerland. The phantom contains in the axial plane four spheres of 5, 6 and 8 mm in diameter with a contrast of 20 HU relative to the background at 120 kV. For statistical reasons, each phantom size was systematically scanned 10 times using local clinical settings of the portal phase for the detection of focal liver lesions (FLL); 40 regions of interest (ROIs) including the target and 150 ROIs with background noise only were extracted. Low contrast detectability (LCD) was objectively assessed using a Channelized Hotelling mathematical model Observer (CHO) with ten dense differences of Gaussian channels for the calculation of a receiver operating characteristic (ROC) curve. For each lesion size, the area under the ROC curve (AUC) was used as a figure of merit (FOM). A new image quality metric, called the weighted AUC (AUC), was proposed to combine the AUC results of all 3 different lesion sizes in a single metric. The displayed CTDIvol was used as a radiation dose metric. Results The median dose used for acquisitions is equal to 5.8 mGy, 10.5 mGy and 16.3 mGy, respectively for the small, medium and large phantoms. For the small phantom, the median image quality is equal to 0.977 with an interquartile range (IQR) equal to 0.027. For the medium phantom the dispersion increased and the median image quality decreased (AUCw = 0.926 and IQR = 0.05). For the large phantom, despite a large range of CTDIvol, the median image quality also decreased (AUCw = 0.89 and IQR = 0.068) and six centers appeared as outliers with relatively limited AUCw scores (AUCw inferior to 0.75), due to very low CTDIvol values. Conclusions The use of a CHO model showed that the majority of institutions performed reasonably well when searching FLL. However, for some outliers, the CTDIvol values were so small that image quality outcomes were clearly not adequate for the intended task. Moreover, the spread of image quality levels was associated with a large CTDIvol distribution, showing that the concept of diagnostic reference levels should be revisited to take into account the image quality aspect. This would ensure comparable diagnostic performance image information content whatever the type of CT unit.

Physicians who frequently perform fluoroscopic examinations are exposed to high intensity radiation fields. The exposure monitoring is performed with a regular personal dosimeter under the apron in order to estimate the effective dose. However, large parts of the body are not protected by the apron (e.g. arms, head). Therefore, it is recommended to wear a supplemental dosimeter over the apron to obtain a better representative estimate of the effective dose. The over-apron dosimeter can also be used to estimate the eye lens dose. The goal of this study was to investigate the relevance of double dosimetry in interventional radiology. First the calibration procedure of the dosimeters placed over the apron was tested. Then, results of double dosimetry during the last five years were analyzed. We found that the personal dose equivalent measured over a lead apron was underestimated by ∼20% to ∼40% for X-ray beam qualities used in radiology. Measurements made over five-year period confirm that the use of a single under-apron dosimeter is inadequate for personnel monitoring. Relatively high skin dose (>10 mSv/month) would have remained undetected without a second dosimeter placed on the apron.

Assessment of image quality for digital x-ray mammography systems used in European screening programs relies mainly on contrast-detail CDMAM phantom scoring and requires the acquisition and analysis of many images in order to reduce variability in threshold detectability. Part II of this study proposes an alternative method based on the detectability index (d') calculated for a non-prewhitened model observer with an eye filter (NPWE). The detectability index was calculated from the normalized noise power spectrum and image contrast, both measured from an image of a 5 cm poly(methyl methacrylate) phantom containing a 0.2 mm thick aluminium square, and the pre-sampling modulation transfer function. This was performed as a function of air kerma at the detector for 11 different digital mammography systems. These calculated d' values were compared against threshold gold thickness (T) results measured with the CDMAM test object and against derived theoretical relationships. A simple relationship was found between T and d', as a function of detector air kerma; a linear relationship was found between d' and contrast-to-noise ratio. The values of threshold thickness used to specify acceptable performance in the European Guidelines for 0.10 and 0.25 mm diameter discs were equivalent to threshold calculated detectability indices of 1.05 and 6.30, respectively. The NPWE method is a validated alternative to CDMAM scoring for use in the image quality specification, quality control and optimization of digital x-ray systems for screening mammography.

The effect of copper (Cu) filtration on image quality and dose in different digital X-ray systems was investigated. Two computed radiography systems and one digital radiography detector were used. Three different polymethylmethacrylate blocks simulated the pediatric body. The effect of Cu filters of 0.1, 0.2, and 0.3 mm thickness on the entrance surface dose (ESD) and the corresponding effective doses (EDs) were measured at tube voltages of 60, 66, and 73 kV. Image quality was evaluated in a contrast-detail phantom with an automated analyzer software. Cu filters of 0.1, 0.2, and 0.3 mm thickness decreased the ESD by 25-32%, 32-39%, and 40-44%, respectively, the ranges depending on the respective tube voltages. There was no consistent decline in image quality due to increasing Cu filtration. The estimated ED of anterior-posterior (AP) chest projections was reduced by up to 23%. No relevant reduction in the ED was noted in AP radiographs of the abdomen and pelvis or in posterior-anterior radiographs of the chest. Cu filtration reduces the ESD, but generally does not reduce the effective dose. Cu filters can help protect radiosensitive superficial organs, such as the mammary glands in AP chest projections.

Diagnostic reference levels (DRLs) were established for 21 indication-based CT examinations for adults in Switzerland. One hundred and seventy-nine of 225 computed tomography (CT) scanners operated in hospitals and private radiology institutes were audited on-site and patient doses were collected. For each CT scanner, a correction factor was calculated expressing the deviation of the measured weighted computed tomography dose index (CTDI) to the nominal weighted CTDI as displayed on the workstation. Patient doses were corrected by this factor providing a realistic basis for establishing national DRLs. Results showed large variations in doses between different radiology departments in Switzerland, especially for examinations of the petrous bone, pelvis, lower limbs and heart. This indicates that the concept of DRLs has not yet been correctly applied for CT examinations in clinical routine. A close collaboration of all stakeholders is mandatory to assure an effective radiation protection of patients. On-site audits will be intensified to further establish the concept of DRLs in Switzerland.

L'index de consommation du glucose, SUV pour standardized uptake value, est largement utilise en tomographie par emission de positons (TEP) pour quantifier la concentration relative de [18F]2-fluoro-2-desoxy-D-glucose (18F-FDG) dans les tissus. Cependant, cet indice depend de nombreux facteurs methodologiques et biologiques et son utilisation fait debat. Il est donc primordial d'instaurer un controle qualite regulier permettant d'assurer la stabilite de la mesure des indices quantitatifs. Dans cette optique, un fantome specifique avec inserts cylindriques de differentes tailles a ete developpe. L'objectif de cette etude est de montrer la sensibilite et l'interet de ce fantome. Methodes. - La sensibilite du fantome a ete etudiee a travers la mesure des SUV et des coefficients de recouvrement (RC). Plusieurs methodes de mesure ont ete utilisees. Les donnees ont ete reconstruites en utilisant les algorithmes de routine clinique. Nous avons etudie la variation des RC en fonction de la taille des cylindres et le changement relatif de fixation, en utilisant des activites differentes. Le fantome a ensuite ete teste sur l'appareil d'un autre centre. Resultats. - Pour toutes les methodes de mesure, une forte variation des RC avec la taille des cylindres, de l'ordre de 50 %, a ete obtenue. Ce fantome a egalement permis de mesurer un changement relatif de fixation qui s'est revele etre independant de la methode de mesure. Malgre un etalonnage des deux systemes TEP/TDM, des differences de quantification d'environ 20 % ont subsiste. Conclusion. - Les resultats obtenus montrent l'interet de ce fantome dans le cadre du suivi des mesures quantitatives.

The aim of this study was to evaluate a low-dose CT with oral contrast medium (LDCT) for the diagnosis of acute appendicitis and compare its performance with standard-dose i.v. contrast-enhanced CT (standard CT) according to patients’ BMIs. Eighty-six consecutive patients admitted with suspicion of acute appendicitis underwent LDCT (30 mAs), followed by standard CT (180 mAs). Both examinations were reviewed by two experienced radiologists for direct and indirect signs of appendicitis. Clinical and surgical follow-up was considered as the reference standard. Appendicitis was confirmed by surgery in 37 (43%) of the 86 patients. Twenty-nine (34%) patients eventually had an alternative discharge diagnosis to explain their abdominal pain. Clinical and biological follow-up was uneventful in 20 (23%) patients. LDCT and standard CT had the same sensitivity (100%, 33/33) and specificity (98%, 45/46) to diagnose appendicitis in patients with a body mass index (BMI) ≥ 18.5. In slim patients (BMI < 18.5), sensitivity to diagnose appendicitis was 50% (2/4) for LDCT and 100% (4/4) for standard CT, while specificity was identical for both techniques (67%, 2/3). LDCT may play a role in the diagnostic workup of patients with a BMI ≥ 18.5.

To retrospectively quantify the effect of systematic use of tube current modulation for neuroradiology computed tomographic (CT) protocols on patient dose and image quality.This HIPAA-compliant study had institutional review board approval, with waiver of informed consent. The authors evaluated the effect of dose modulation on four types of neuroradiologic CT studies: brain CT performed without contrast material (unenhanced CT) in adult patients, unenhanced brain CT in pediatric patients, adult cervical spine CT, and adult cervical and intracranial CT angiography. For each type of CT study, three series of 100 consecutive studies were reviewed: 100 studies performed without dose modulation, 100 studies performed with z-axis dose modulation, and 100 studies performed with x-y-z-axis dose modulation. For each examination, the weighted volume CT dose index (CTDI(vol)) and dose-length product (DLP) were recorded and noise was measured. Each study was also reviewed for image quality. Continuous variables (CTDI(vol), DLP, noise) were compared by using t tests, and categorical variables (image quality) were compared by using Wilcoxon rank-sum tests.For unenhanced CT of adult brains, the CTDI(vol) and DLP, respectively, were reduced by 60.9% and 60.3%, respectively, by using z-axis dose modulation and by 50.4% and 22.4% by using x-y-z-axis dose modulation. Significant dose reductions (P.001) were also observed for pediatric unenhanced brain CT, cervical spine CT, and adult cervical and intracranial CT angiography performed with each dose modulation technique. Image quality and noise were unaffected by the use of either dose modulation technique (P.05).Use of dose-modulation techniques for neuroradiology CT examinations affords significant dose reduction while image quality is maintained.

This work aimed at assessing the doses delivered in Switzerland to paediatric patients during computed tomography (CT) examinations of the brain, chest and abdomen, and at establishing diagnostic reference levels (DRLs) for various age groups. Forms were sent to the ten centres performing CT on children, addressing the demographics, the indication and the scanning parameters: number of series, kilovoltage, tube current, rotation time, reconstruction slice thickness and pitch, volume CT dose index (CTDI(vol)) and dose length product (DLP). Per age group, the proposed DRLs for brain, chest and abdomen are, respectively, in terms of CTDI(vol): 20, 30, 40, 60 mGy; 5, 8, 10, 12 mGy; 7, 9, 13, 16 mGy; and in terms of DLP: 270, 420, 560, 1,000 mGy cm; 110, 200, 220, 460 mGy cm; 130, 300, 380, 500 mGy cm. An optimisation process should be initiated to reduce the spread in dose recorded in this study. A major element of this process should be the use of DRLs.

As the number and complexity of fluoroscopically guided interventions increase, a serious effort has to be put on the optimisation of the X-ray dose delivered to the patient. In order to set up this optimisation process, the clinical practice for a given cardiology centre has to be analysed with relevant statistical power and compared with the data at local or national level. Data from 8 Swiss cardiology centres for 10 different vascular and heart rhythm procedures have been collected. The collected dose indicators were, when available, cumulated air kerma, cumulated dose-area product, fluoroscopy time and the number of images per procedure. Data analysis was performed using an in-house software solution in terms of the first, second and third quartiles. This kind of large-scale analysis could yield some onsets towards local practice optimisation based on anonymous dose indicator cross-comparison. Further effort should nevertheless be made in order to proceed towards an operator-based data analysis, thus allowing for an individual practice optimisation.

We sought to compare operator radiation exposure during procedures using right femoral access (RFA), right radial access (RRA), and left radial access (LRA) during coronary angiography (CA) and percutaneous coronary intervention (PCI). Because of an increased incidence of long-term malignancy in interventional cardiologists, operator radiation exposure is of rising concern. This prospective study included all consecutive patients who underwent elective or emergency CA ± PCI from September 2014 to March 2015. The primary end point was operator radiation exposure, quantified as the ratio of operator cumulative dose (CD) and patient radiation reported as dose-area product (DAP) (CD/DAP). Secondary end points included CD, DAP, and fluoroscopy time (FT). Overall 830 procedures (457 CA [55%] and 373 PCI [45%]) were performed, 455 (55%) through RFA, 272 (33%) through RRA, and 103 (12%) through LRA. The CD/DAP was lower in RFA (0.09 μSv/Gycm² [0.02 to 0.20]) compared with RRA (0.47 μSv/Gycm² [0.25 to 0.75], p

Purpose To avoid unnecessary exposure to the patients, constructors have developed tube current modulation algorithms. The purpose of this work is to assess the performance of computed tomography (CT) tube current modulation concerning patient dose and image noise in MSCT scanners. Material and methods A conical PMMA phantom with elliptical cross-section, to vary the thickness of the irradiated object in a monotonous way, and an anthropomorphic chest phantom were scanned under similar conditions on a general electrics (GE) LightSpeed VCT (64 slices) scanner. Noise measurements were made by calculating the standard deviation of the CT-number on a homogeneous ROI in both phantoms. The dose was estimated with the parameters read in the DICOM header of each studied image. Results The study has shown that most of the time, constant noise levels (noise index) can be obtained by a variation of the mA. Nevertheless, this adaptation can be not fast enough when the variation of the attenuation changes is rapid. Thus, an adaptation length up to 5 cm was obtained. A 18% dose reduction can be achieved (mean of 9.9%) by switching from z -axis modulation algorithm to xyz -axis modulation option. However, exposure in the chest area can be higher with current modulation than without, when trying to keep an image noise level constant in thoraco-abdominal investigations. Conclusion Current modulation algorithms can produce inadequate quality images due to problems with tube current stabilization when a sudden attenuation variation takes place as at the start of a scanning sequence. As expected, rotational ( xyz -axis) modulation performs better than only z -axis modulation algorithm. The use of automatic exposure control (AEC) can lead to an increase of the dose if the maximum allowed current is not properly set in thoraco-abdominal acquisitions.

Resume L’objectif du travail etait la caracterisation de deux installations TEP/TDM, basees sur des technologies differentes, sur la base du protocole propose dans la norme NEMA NU 2-2001. Les deux systemes ont ete qualifies en mode d’acquisition 3D en utilisant les fantomes de la National Electric Manufacturers Association (NEMA). Les resultats obtenus montrent que la norme NEMA permet de mettre en evidence des differences entre la resolution spatiale, la sensibilite, la fraction de diffuse et les performances en taux de comptage des deux systemes, differences attribuables a la geometrie et aux materiaux des detecteurs utilises. Ainsi, l’utilisation de la norme permet d’etablir de veritables points de reference des systemes. Les tests de qualite d’image, obtenus dans des conditions plus proches des applications cliniques montrent que les deux installations, en depit de leurs differences de technologies, produisent, dans des temps d’acquisition courts, des images suffisamment contrastees pour permettre la detection de petites lesions. Ce test devrait d’ailleurs faire partie des tests de stabilite pour assurer la comparaison des examens, lorsque les aspects quantitatifs sont d’importance.

The purpose of this article was to review the strategies to control patient dose in adult and pediatric computed tomography (CT), taking into account the change of technology from single-detector row CT to multi-detector row CT. First the relationships between computed tomography dose index, dose length product, and effective dose in adult and pediatric CT are revised, along with the diagnostic reference level concept. Then the effect of image noise as a function of volume computed tomography dose index, reconstructed slice thickness, and the size of the patient are described. Finally, the potential of tube current modulation CT is discussed.

Combined positron emission tomography and computed tomography (PET/CT) scanners play a major role in medicine for in vivo imaging in an increasing number of diseases in oncology, cardiology, neurology, and psychiatry. With the advent of short-lived radioisotopes other than {sup 18}F and newer scanners, there is a need to optimize radioisotope activity and acquisition protocols, as well as to compare scanner performances on an objective basis. The Discovery-LS (D-LS) was among the first clinical PET/CT scanners to be developed and has been extensively characterized with older National Electrical Manufacturer Association (NEMA) NU 2-1994 standards. At the time of publication of the latest version of the standards (NU 2-2001) that have been adapted for whole-body imaging under clinical conditions, more recent models from the same manufacturer, i.e., Discovery-ST (D-ST) and Discovery-STE (D-STE), were commercially available. We report on the full characterization both in the two- and three-dimensional acquisition mode of the D-LS according to latest NEMA NU 2-2001 standards (spatial resolution, sensitivity, count rate performance, accuracy of count losses, and random coincidence correction and image quality), as well as a detailed comparison with the newer D-ST widely used and whose characteristics are already published.

— A nationwide investigation was conducted in Switzerland to establish the exposure of the population by medical x rays and update the results of the 1998 survey. Both the frequency and the dose variations were studied in order to determine the change in the collective dose. The frequency study addressed 206 general practitioners (GPs), 30 hospitals, and 10 private radiology institutes. Except for the latter, the response rate was very satisfactory. The dose study relied on the assessment of the speed class of the screen-film combinations used by the GPs as well as the results of two separate studies dedicated to fluoroscopy and CT. The investigation showed that the total number of all medical x-ray examinations performed by GPs registered a 1% decrease between 1998 and 2003, and that the sensitivities of the film-screen combinations registered a shift towards higher values, leading to a reduction of the dose delivered by a GP of the order of 20%. The study indicated also that the total number of all x-ray examinations performed in hospitals increased by 4%, with a slight increase of radiographies by 1% but significant decrease of examinations involving fluoroscopy (39%), and a 70% increase for CT examinations. Concerning the doses, the investigation of a selection of examinations involving fluoroscopy showed a significant increase of the kerma-area product (KAP) per procedure. For CT the study showed an increase of the dose-length product (DLP) per procedure for skull and abdomen examinations, and a decrease for chest examination. Both changes in the frequency and the effective dose per examination led to a 20% increase in the total collective dose.

An objective analysis of image quality parameters was performed for six digital mammography systems. The presampled modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE) for the systems were determined at different doses, for 28 kVp with a Mo/Mo or W/Al target/filter combination and 2 mm of additional aluminium filtration. The flat-panel units have higher MTF and DQE in the mid to high frequency range than standard CR systems. The highest DQE, over the whole dose range, is for the slit-scanning direct photon counting system. Dual-side read CR can overcome the inherent x-ray absorption and signal collection limitations of standard CR mammography, improving the low-frequency DQE by 40%, to the same level as full-field systems, but it does not improve the poor spatial resolution of phosphor.

Evaluation of image quality (IQ) in Computed Tomography (CT) is important to ensure that diagnostic questions are correctly answered, whilst keeping radiation dose to the patient as low as is reasonably possible. The assessment of individual aspects of IQ is already a key component of routine quality control of medical x-ray devices. These values together with standard dose indicators can be used to give rise to 'figures of merit' (FOM) to characterise the dose efficiency of the CT scanners operating in certain modes. The demand for clinically relevant IQ characterisation has naturally increased with the development of CT technology (detectors efficiency, image reconstruction and processing), resulting in the adaptation and evolution of assessment methods. The purpose of this review is to present the spectrum of various methods that have been used to characterise image quality in CT: from objective measurements of physical parameters to clinically task-based approaches (i.e. model observer (MO) approach) including pure human observer approach. When combined together with a dose indicator, a generalised dose efficiency index can be explored in a framework of system and patient dose optimisation. We will focus on the IQ methodologies that are required for dealing with standard reconstruction, but also for iterative reconstruction algorithms. With this concept the previously used FOM will be presented with a proposal to update them in order to make them relevant and up to date with technological progress. The MO that objectively assesses IQ for clinically relevant tasks represents the most promising method in terms of radiologist sensitivity performance and therefore of most relevance in the clinical environment. publisher: Elsevier articletitle: Image quality in CT: From physical measurements to model observers journaltitle: Physica Medica articlelink: http://dx.doi.org/10.1016/j.ejmp.2015.08.007 content_type: article copyright: Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Associazione Italiana di Fisica in Medicina ispartof: Physica Medica vol:31 issue:8 pages:823-843 ispartof: location:Italy status: published

In recent years, technological advances have allowed manufacturers to implement dual-energy computed tomography (DECT) on clinical scanners. With its unique ability to differentiate basis materials by their atomic number, DECT has opened new perspectives in imaging. DECT has been used successfully in musculoskeletal imaging with applications ranging from detection, characterization, and quantification of crystal and iron deposits; to simulation of noncalcium (improving the visualization of bone marrow lesions) or noniodine images. Furthermore, the data acquired with DECT can be postprocessed to generate monoenergetic images of varying kiloelectron volts, providing new methods for image contrast optimization as well as metal artifact reduction. The first part of this article reviews the basic principles and technical aspects of DECT including radiation dose considerations. The second part focuses on applications of DECT to musculoskeletal imaging including gout and other crystal-induced arthropathies, virtual noncalcium images for the study of bone marrow lesions, the study of collagenous structures, applications in computed tomography arthrography, as well as the detection of hemosiderin and metal particles.

Computed tomography (CT) is a modality of choice for the study of the musculoskeletal system for various indications including the study of bone, calcifications, internal derangements of joints (with CT arthrography), as well as periprosthetic complications. However, CT remains intrinsically limited by the fact that it exposes patients to ionizing radiation. Scanning protocols need to be optimized to achieve diagnostic image quality at the lowest radiation dose possible. In this optimization process, the radiologist needs to be familiar with the parameters used to quantify radiation dose and image quality. CT imaging of the musculoskeletal system has certain specificities including the focus on high-contrast objects (i.e., in CT of bone or CT arthrography). These characteristics need to be taken into account when defining a strategy to optimize dose and when choosing the best combination of scanning parameters. In the first part of this review, we present the parameters used for the evaluation and quantification of radiation dose and image quality. In the second part, we discuss different strategies to optimize radiation dose and image quality at CT, with a focus on the musculoskeletal system and the use of novel iterative reconstruction techniques.

In recent years, technological advances have allowed manufacturers to implement dual-energy computed tomography (DECT) on clinical scanners. With its unique ability to differentiate basis materials by their atomic number, DECT has opened new perspectives in imaging. DECT has been successfully used in musculoskeletal imaging with applications ranging from detection, characterization, and quantification of crystal and iron deposits, to simulation of noncalcium (improving the visualization of bone marrow lesions) or noniodine images. Furthermore, the data acquired with DECT can be postprocessed to generate monoenergetic images of varying kiloelectron volts, providing new methods for image contrast optimization as well as metal artifact reduction. The first part of this article reviews the basic principles and technical aspects of DECT including radiation dose considerations. The second part focuses on applications of DECT to musculoskeletal imaging including gout and other crystal-induced arthropathies, virtual noncalcium images for the study of bone marrow lesions, the study of collagenous structures, applications in computed tomography arthrography, as well as the detection of hemosiderin and metal particles.

Signal detection on 3D medical images depends on many factors, such as foveal and peripheral vision, the type of signal, and background complexity, and the speed at which the frames are displayed. In this paper, the authors focus on the speed with which radiologists and naïve observers search through medical images. Prior to the study, the authors asked the radiologists to estimate the speed at which they scrolled through CT sets. They gave a subjective estimate of 5 frames per second (fps). The aim of this paper is to measure and analyze the speed with which humans scroll through image stacks, showing a method to visually display the behavior of observers as the search is made as well as measuring the accuracy of the decisions. This information will be useful in the development of model observers, mathematical algorithms that can be used to evaluate diagnostic imaging systems.The authors performed a series of 3D 4-alternative forced-choice lung nodule detection tasks on volumetric stacks of chest CT images iteratively reconstructed in lung algorithm. The strategy used by three radiologists and three naïve observers was assessed using an eye-tracker in order to establish where their gaze was fixed during the experiment and to verify that when a decision was made, a correct answer was not due only to chance. In a first set of experiments, the observers were restricted to read the images at three fixed speeds of image scrolling and were allowed to see each alternative once. In the second set of experiments, the subjects were allowed to scroll through the image stacks at will with no time or gaze limits. In both static-speed and free-scrolling conditions, the four image stacks were displayed simultaneously. All trials were shown at two different image contrasts.The authors were able to determine a histogram of scrolling speeds in frames per second. The scrolling speed of the naïve observers and the radiologists at the moment the signal was detected was measured at 25-30 fps. For the task chosen, the performance of the observers was not affected by the contrast or experience of the observer. However, the naïve observers exhibited a different pattern of scrolling than the radiologists, which included a tendency toward higher number of direction changes and number of slices viewed.The authors have determined a distribution of speeds for volumetric detection tasks. The speed at detection was higher than that subjectively estimated by the radiologists before the experiment. The speed information that was measured will be useful in the development of 3D model observers, especially anthropomorphic model observers which try to mimic human behavior.

Task-based medical image quality is often assessed by model observers for single slice images. The goal of the study was to determine if model observers can predict human detection performance of low contrast signals in CT for clinical multi-slice (ms) images. We collected 24 different data subsets from a low contrast phantom: 3 dose levels (40, 90, 150 mAs), 4 signals (6 and 8 mm diameter; 10 and 20 HU at 120kV) and 2 reconstruction algorithms (FBP and iterative (IR)). Images were assessed by human and model observers in 4-alternative forced choice (4AFC) experiments with ms data set in a signal-known-exactly (SKE) paradigm. Model observers with single (msCHOa) and multiple (msCHOb) templates were implemented in a train and test method analysis with Dense Difference of Gaussian (DDoG) and Gabor spatial channels. For human observers, we found that percent correct increased with the dose and was higher for iterative reconstructed images than FBP in all investigated conditions. All model observers implemented overestimated human performance in any condition except one case (6mm and 10HU) for msCHOa and msCHOb with Gabor channels. Internal noise could be implemented and a good agreement was found but necessitates independent fits according to the reconstruction method. Generally msCHOb shows higher detection performance than msCHOa with both types of channels. Gabor channels were less efficient than DDoG in this context. These results allow further developments in 3D analysis technique for low contrast CT.

Resume But Cette etude analyse la pratique du scanner en Suisse. Materiel et methodes A l’aide de differentes sources (donnees administratives sur les equipements, enquete exhaustive sur les pratiques en 1998, donnees fournies par les hopitaux universitaires suisses de Bâle, de Zurich et de Lausanne), nous avons determine la frequence d’examens scanner en 1998 selon plusieurs variables descriptives et documente l’evolution de cette pratique dans le temps. Resultats L’equipement en scanner a augmente de 7% entre 1998 et 2004. Le nombre annuel moyen d’examens de scanner en Suisse est de 46,3/1 000 hab. soit 3,4% des examens radiologiques pour 1997-1998. L’examen le plus frequent est celui du crâne (24%) alors que dans le sous-groupe des instituts de radiologue c’est plutot celui du rachis. Le sex-ratio (H/F) est de 1,17. L’augmentation annuelle moyenne de la pratique du scanner dans les hopitaux en Suisse varie de 8% a Bâle (1997-2003) a 18% a Lausanne (1992-2004). Enfin, la part des examens pediatriques est estimee a 5% (donnees de Lausanne), leur nombre a tendance a se stabiliser. Conclusion Le nombre d’examens de scanner realises en Suisse est en constante augmentation depuis plusieurs annees. Cette etude descriptive permet de sensibiliser les medecins aux examens de scanners dans le but d’optimiser leur utilisation.

An objective analysis of image quality parameters was performed for a computed radiography (CR) system using both standard single-side and prototype dual-side read plates. The pre-sampled modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) for the systems were determined at three different beam qualities representative of pediatric chest radiography, at an entrance detector air kerma of 5 {mu}Gy. The NPS and DQE measurements were realized under clinically relevant x-ray spectra for pediatric radiology, including x-ray scatter radiations. Compared to the standard single-side read system, the MTF for the dual-side read system is reduced, but this is offset by a significant decrease in image noise, resulting in a marked increase in DQE (+40%) in the low spatial frequency range. Thus, for the same image quality, the new technology permits the CR system to be used at a reduced dose level.

To evaluate a low-dose abdominal computed tomography (LDCT) protocol, delivering a radiation dose close to that delivered by an abdominal plain film (APF), in patients with a clinical suspicion of renal colic.A total of 139 patients for whom an APF was requested for suspicion of renal colic were randomized into two groups. The patients in group 1 (n = 68) underwent an admission LDCT scan delivering a 2.1-mSv radiation dose to women and 1.6 mSv to men, instead of the APF. Patients in group 2 (n = 71) underwent an APF. Clinical and radiologic follow-up data were obtained for each patient. The number of additional abdominal ultrasound and CT scans performed to reach a confident final diagnosis and determine the proper treatment was compared between the two groups. A mean effective radiation dose was obtained in each group.Of the 68 patients in group 1 (LDCT), 10 (15%) underwent ultrasonography, 9 (13%) conventional abdominal CT, and 2 (3%) both. In group 2 (APF), the corresponding percentages were 27% (19 of 71), 28% (20 of 71), and 23% (16 of 71). Of the 68 patients in group 1, 47 (69%) did not require any additional examinations compared with 16 (23%) of the 71 patients in group 2 (P0.0001). The mean effective dose was 3.5 and 6.9 mSv in groups 1 and 2, respectively (P0.0001).In patients with suspicion of renal colic, replacing the admission APF with our LDCT protocol will significantly reduce the need for additional CT or ultrasonography. Also, our LDCT protocol decreases by almost 50% the mean radiation dose per patient.

Imaging of biological samples has been performed with a variety of techniques for example electromagnetic waves, electrons, neutrons, ultrasound and X-rays. Also conventional X-ray imaging represents the basis of medical diagnostic imaging, it remains of limited use in this application because it is based solely on the differential absorption of X-rays by tissues. Coherent and bright photon beams, such as those produced by third-generation synchrotron X-ray sources, provide further information on subtle X-ray phase changes at matter interfaces. This complements conventional X-ray absorption by edge enhancement phenomena. Thus, phase contrast imaging has the potential to improve the detection of structures on images by detecting those structures that are invisible with X-ray absorption imaging. Images of a weakly absorbing nylon fibre were recorded in in-line holography geometry using a high resolution low-noise CCD camera at the ESRF in Grenoble. The method was also applied to improve image contrast for images of biological tissues. This paper presents phase contrast microradiographs of vascular tree casts and images of a housefly. These reveal very fine structures, that remain invisible with conventional absorption contrast only.

Three standard radiation qualities (RQA 3, RQA 5 and RQA 9) and two screens, Kodak Lanex Regular and Insight Skeletal, were used to compare the imaging performance and dose requirements of the new Kodak Hyper Speed G and the current Kodak T-MAT G/RA medical x-ray films. The noise equivalent quanta (NEQ) and detective quantum efficiencies (DQE) of the four screen-film combinations were measured at three gross optical densities and compared with the characteristics for the Kodak CR 9000 system with GP (general purpose) and HR (high resolution) phosphor plates. The new Hyper Speed G film has double the intrinsic sensitivity of the T-MAT G/RA film and a higher contrast in the high optical density range for comparable exposure latitude. By providing both high sensitivity and high spatial resolution, the new film significantly improves the compromise between dose and image quality. As expected, the new film has a higher noise level and a lower signal-to-noise ratio than the standard film, although in the high frequency range this is compensated for by a better resolution, giving better DQE results--especially at high optical density. Both screen-film systems outperform the phosphor plates in terms of MTF and DQE for standard imaging conditions (Regular screen at RQA 5 and RQA 9 beam qualities). At low energy (RQA 3), the CR system has a comparable low-frequency DQE to screen-film systems when used with a fine screen at low and middle optical densities, and a superior low-frequency DQE at high optical density.

To prospectively compare the accuracy of 16-detector row computed tomographic (CT) angiography with conventional digital subtraction angiography (DSA) as the reference standard in the assessment of aortoiliac and lower extremity arteries in patients with peripheral arterial disease.This study was approved by the institutional review board, and informed consent was obtained. A total of 39 consecutive patients (27 men [mean age, 66 years] and 12 women [mean age, 64 years]) with peripheral arterial disease underwent both conventional DSA and 16-detector row CT angiography. For data analysis, the arterial vascular system was divided into 35 segments. A total of 1365 arterial segments were analyzed for arterial stenosis by two independent blinded readers using a four-point grading system (grade 1,10% luminal narrowing; grade 2, 10%-49% luminal narrowing; grade 3, 50%-99% luminal narrowing; grade 4, occlusion). Interobserver agreements were calculated by using kappa statistics. A third independent blinded reader assessed possible reasons for disagreements between 16-detector row CT angiographic findings and conventional DSA findings. Effective radiation dose was calculated for both imaging modalities.Sixteen-detector row CT angiographic and conventional DSA findings were diagnostic in all vascular segments. Compared with conventional DSA, the sensitivity and specificity of 16-detector row CT angiography with regard to detection of hemodynamically significant stenosis in all 35 arterial segments were 96% and 97%, respectively, for both readers. Readers 1 and 2 overestimated arterial stenosis in 42 (3%) and 34 (2%) arterial segments, respectively, and underestimated arterial stenosis in 13 (1%) and 10 (1%) arterial segments, respectively. Interobserver agreement was excellent (kappa = 0.84-1.00). Presence of anteroposteriorly located luminal narrowing and extensive vascular wall calcification were considered main reasons for disagreements between imaging modalities. Effective radiation dose was lower for 16-detector row CT angiography (1.6-3.9 mSv) than for conventional DSA (6.4-16.0 mSv).Sixteen-detector row CT angiography is an accurate and reliable noninvasive alternative to conventional DSA in the assessment of aortoiliac and lower extremity arteries in patients with peripheral arterial disease.

The purpose of this work was to compare standard desktop display systems with dedicated medical display systems. The set of image tests proposed by the American Association of Physicists in Medicine (AAPM TG18) was used to assess a Philips 107S desktop display system and a Siemens medical display. Three observers performed the subjective assessment, in a non-concerted manner. The objective assessment was performed using a CCD camera according to the AAPM TG18 procedure. The results clearly demonstrate the inadequacy of standard desktop display systems in the framework of diagnostic radiology. Moreover, a good correlation between the subjective and objective assessment methods was obtained.

The RADIUS (Radiological Imaging Unification Strategy) project addresses the assessment of image quality in terms of both physical and clinically relevant measures. The aim is to unify our understanding of both types of measure as well as the numerous underlying factors that play a key role in the assessments of imaging performance. In this way it is expected to provide a solid basis for the improvement in radiological safety management, where not only radiation risks are considered but also diagnostic risks of incorrect clinical outcomes (i.e. false positive/false negative). The project has applied a variety of relevant experimental and theoretical methods to this problem, which is generic to medical imaging as a whole. Digital radiography of the chest and the breast has been employed as the clinical imaging domain vehicles for the study. The project addressed the problem from the following directions: role and relevance of pathology, human observer studies including receiver operating characteristics, image quality criteria analysis, structural noise analysis, physical measurements on clinical images, physical measurements on imaging system, modelling of imaging system, modelling of visual processes, modelling of doses delivered and IT-based scientific support strategies. This paper presents an overview of the main outcomes from this project and highlights how the research outcomes actually apply to the real world. In particular, attention will be focused on new and original findings and methods and techniques that have been developed within the framework of the project. The relevance of the project's outcomes to future European research will also be presented.

PURPOSE: It is generally assumed that the biodistribution and pharmacokinetics of radiolabelled antibodies remain similar between dosimetric and therapeutic injections in radioimmunotherapy. However, circulation half-lives of unlabelled rituximab have been reported to increase progressively after the weekly injections of standard therapy doses. The aim of this study was to evaluate the evolution of the pharmacokinetics of repeated 131I-rituximab injections during treatment with unlabelled rituximab in patients with non-Hodgkin's lymphoma (NHL). METHODS: Patients received standard weekly therapy with rituximab (375 mg/m2) for 4 weeks and a fifth injection at 7 or 8 weeks. Each patient had three additional injections of 185 MBq 131I-rituximab in either treatment weeks 1, 3 and 7 (two patients) or weeks 2, 4 and 8 (two patients). The 12 radiolabelled antibody injections were followed by three whole-body (WB) scintigraphic studies during 1 week and blood sampling on the same occasions. Additional WB scans were performed after 2 and 4 weeks post 131I-rituximab injection prior to the second and third injections, respectively. RESULTS: A single exponential radioactivity decrease for WB, liver, spleen, kidneys and heart was observed. Biodistribution and half-lives were patient specific, and without significant change after the second or third injection compared with the first one. Blood T(1/2)beta, calculated from the sequential blood samples and fitted to a bi-exponential curve, was similar to the T(1/2) of heart and liver but shorter than that of WB and kidneys. Effective radiation dose calculated from attenuation-corrected WB scans and blood using Mirdose3.1 was 0.53+0.05 mSv/MBq (range 0.48-0.59 mSv/MBq). Radiation dose was highest for spleen and kidneys, followed by heart and liver. CONCLUSION: These results show that the biodistribution and tissue kinetics of 131I-rituximab, while specific to each patient, remained constant during unlabelled antibody therapy. RIT radiation doses can therefore be reliably extrapolated from a preceding dosimetry study.

Four standard radiation qualities (from RQA 3 to RQA 9) were used to compare the imaging performance of a computed radiography(CR)system (general purpose and high resolution phosphor plates of a Kodak CR 9000 system), a selenium-based direct flat panel detector (Kodak Direct View DR 9000), and a conventional screen-film system (Kodak T-MAT L/RA film with a 3M Trimax Regular screen of speed 400) in conventional radiography. Reference exposure levels were chosen according to the manufacturer’s recommendations to be representative of clinical practice (exposure index of 1700 for digital systems and a film optical density of 1.4). With the exception of the RQA 3 beam quality, the exposure levels needed to produce a mean digital signal of 1700 were higher than those needed to obtain a mean film optical density of 1.4. In spite of intense developments in the field of digital detectors, screen-film systems are still very efficient detectors for most of the beam qualities used in radiology. An important outcome of this study is the behavior of the detective quantum efficiency of the digital radiography (DR) system as a function of beam energy. The practice of users to increase beam energy when switching from a screen-film system to a CRsystem, in order to improve the compromise between patient dose and image quality, might not be appropriate when switching from screen-film to selenium-based DR systems.

The purpose of this study was to compare the diagnostic performance of axial and coronal views in multidetector CT enteroclysis (MDCTE). We retrospectively evaluated 48 patients with pathological correlation investigated by MDCTE for small bowel disorders. After nasojejunal administration of 2 l of 5% methylcellulose axial arterial and venous acquisition of MDCTE was followed by coronal reconstructions using equal slice thicknesses of 2.5 mm with 2 mm increments. Spatial resolution of both planes was evaluated by phantom. Three radiologists independently read axial and coronal images concerning 12 pathological features. The interobserver agreement and time of reading was calculated. Sensitivity and specificity resulted from comparison with histopathology (n=39) or follow-up (n=9). Phantom study revealed higher spatial resolution for axial than coronal views, whatever reconstruction interval was used. However, spatial frequency always remained high. Most pathological signs, such as bowel wall thickening (BWT), bowel wall enhancement (BWE) and intraperitoneal fluid (IPF), showed better interobserver agreement on axial than coronal views (BWT: 0.61 vs. 0.44; BWE: 0.56 vs. 0.5; IPF:0.53 vs. 0.43). The Wilcoxon signed-rank test revealed significantly higher sensitivity for axial than coronal views (P=0.0453); the time of reading was significantly shorter for the latter (P=0.0146). The diagnostic value of axial slices is superior to coronal reconstructions despite the reduced data volume and display of the physiological course of bowel loops on the coronal plane.

Our objective is to describe a new test phantom that permits the objective assessment of image quality in conventional and digital mammography for different types of breast tissue. A test phantom, designed to represent a compressed breast, was made from tissue equivalent materials. Three separate regions, with different breast tissue compositions, are used to evaluate low and high contrast resolution, spatial resolution and image noise. The phantom was imaged over a range of kV using a Contour 2000 (Bennett) mammography unit with a Kodak MinR 2190-MinR L screen-film combination and a Senograph 2000D (General Electric) digital mammography unit. Objective image quality assessments for different breast tissue compositions were performed using the phantom for conventional and digital mammography. For a similar mean glandular dose (MGD), the digital system gives a significantly higher contrast-to-noise ratio (CNR) than the screen-film system for 100% glandular tissue. In conclusion, in mammography, a range of exposure conditions is used for imaging because of the different breast tissue compositions encountered clinically. Ideally, the patient dose-image quality relationship should be optimized over the range of exposure conditions. The test phantom presented in this work permits image quality parameters to be evaluated objectively for three different types of breast tissue. Thus, it is a useful tool for optimizing the patient dose-image quality relationship.

To evaluate the influence of different reconstruction intervals of retrospectively electrocardiographically (ECG)-gated multi-detector row computed tomographic (CT) angiography on image quality of different segments of various types of coronary artery bypass grafts.Twenty consecutive patients with 62 grafts underwent retrospectively ECG-gated four-channel multi-detector row CT angiography and conventional coronary angiography. Raw helical CT data were reconstructed at 0%-90% of the cardiac cycle in increments of 10%. Each graft was separated into three segments (proximal segment, graft body, and distal anastomosis). Three graft types were identified according to site of distal anastomosis. Two readers assessed image quality of segments and graft types. Effective radiation dose was calculated.Best image quality of all segments was obtained at a reconstruction interval of 50%-70% of the cardiac cycle. Image quality of the proximal segment did not vary significantly with different reconstruction intervals (analysis of variance, P =.8), whereas image quality of the graft body and distal anastomosis changed significantly with varying reconstruction intervals (P.001). Distal anastomosis and body of types 1 and 2 grafts were best seen at 60%-70% of the cardiac cycle, whereas distal anastomosis and body of type 3 grafts were best visualized at 50%. Accuracy of CT angiography for detection of graft patency was 94% for reader 1 and 95% for reader 2. Effective dose for CT was 11.4 mSv for both men and women. Mean effective dose for angiography was 2.1 mSv for men and women.Optimal selection of reconstruction interval improves image quality of the graft body and of distal anastomosis in particular.

Objective. The objective of this study was to assess the age-related variations of brain perfusion through quantitative cerebral perfusion computed tomography (CT) results in children without brain abnormality. Methods. Brain perfusion CT examinations were performed in 77 children, aged 7 days to 18 years. These patients were admitted at our institution for both noncontrast and contrast-enhanced cerebral CT. Only children whose conventional cerebral CT and clinical/radiologic follow-up, including additional investigations, were normal were taken into account for this study (53 of 77). Results. The average regional rCBF amounts to 40 (mL/100 g per minute) for the first 6 months of life, peaks at ∼130 (mL/100 g per minute) at ∼2 to 4 years of age, and finally stabilizes at ∼50 (mL/100 g per minute) at ∼7 to 8 years of age, with a small increase of rCBF values at ∼12 years of age. The rCBF in the gray matter averages 3 times that in the white matter, except for the first 6 months of life. The global CBF represents 10% to 20% of the global cardiac output for the first 6 months of life, peaks at ∼55% by 2 to 4 years of age, and finally stabilizes at ∼15% by 7 to 8 years of age. Specific age-related evolution patterns were identified in the different anatomic areas of the cerebral parenchyma, which could be related to the development of neuroanatomic structures and to the emergence of corresponding cognitive functions. Conclusions. Quantitative perfusion CT characterization of brain perfusion shows specific age variations. Brain perfusion of each cortical area evolves according to a specific time course, in close correlation with the psychomotor development.

The aim of this study was to model the edge enhancement effect in in-line holography phase contrast imaging. A simple analytical approach was used to quantify refraction and interference contrasts in terms of beam energy and imaging geometry. The model was applied to predict the peak intensity and frequency of the edge enhancement for images of cylindrical fibers. The calculations were compared with measurements, and the relationship between the spatial resolution of the detector and the amplitude of the phase contrast signal was investigated. Calculations using the analytical model were in good agreement with experimental results for nylon, aluminum and copper wires of 50 to 240 microm diameter, and with numerical simulations based on Fresnel-Kirchhoff theory. A relationship between the defocusing distance and the pixel size of the image detector was established. This analytical model is a useful tool for optimizing imaging parameters in phase contrast in-line holography, including defocusing distance, detector resolution and beam energy.

Radiation protection is assured by respecting three general principles which are: the justification of the practice; the optimisation of the protection; and the individual dose limits. The justification of the practice is due to the fact that exposure to ionising radiation has deleterious effects on health. The principle of optimisation is introduced since some of these effects are considered as non-threshold ones, and thus one has to reduce exposure to levels as low as reasonably achievable (i.e. ALARA principle). The principle of individual limits is introduced as a safeguard to prevent situations where the respect of the two first principles would not be sufficient to protect individuals. The first objective of this contribution is to state the dose limits for exposure of diagnostic imaging personnel and explain the reasons for allowing a larger dose equivalent for radiation workers than for the general population. The second objective is to present various methods and devices that may be used to reduce personnel exposure during diagnostic X-ray examinations (especially interventional fluoroscopic procedures). A judicious application of radiation protection techniques, such as the limitation of patient exposure, the increase of the distance from the source of scatter, and shielding, will significantly reduce personnel exposure.

Introduction In the last decade, technological breakthroughs in CT allow an improvement of optimization process. With the introduction of iterative algorithms, an adjustment of clinical protocols has been achieved. Classical metrics were become insufficient to assess image quality of clinical protocols. An objective method, based on a clinical task has to be used. The goal of this study is to evaluate abdominal protocols on two newest CT, using a mathematical model observer. We can also underline the impact of a fully model-based iterative reconstruction algorithm when dealing with low-contrast detectability tasks. Method An anthropomorphic abdominal phantom (equivalent o 24 cm) with 8 and 5 mm low contrast targets (20 HU) was scanned on two CT systems: Revolution CT and CT750 HD, GE Healthcare. Peripheral rings (2.5 and 5 cm in thickness) were added to simulate different patient sizes. The phantom was scanned 15 times using a routine abdominal protocol with a slice thickness of 2.5 mm (0.625 mm for VEO® (MBIR algorithm); avoiding any MPR processing). On both units, the noise index was adjusted with the phantom’s size (i.e. 20, 26 and 32 HU). Images were reconstructed using FBP, ASIR50% and VEO® for CT750HD and ASIR-V at 0% and 50% for Revolution CT. To assess low-contrast detectability, a Channelized Hotelling Observer (CHO; 10 DDOG channels) was used. The area under the curve (AUC) index was chosen as figure of merit (FOM). Results Scanning the phantom on the CT750 HD, no significant difference appeared between FBP and ASIR50%. For the largest phantom size, a significant increase of 6% in low contrast detectability was recorded on 5mm targets using VEO (with a longitudinal spatial resolution four times higher) compared to ASIR50%. Concerning the Revolution CT no difference in detectability was noted between ASIR-V at 0% and 50%. Comparing the two CT systems the displayed CTDIvol values for the Revolution CT were systematically lower than for the CT750HD (reaching 40% for the thickest phantom). Low contrast detectability performances were comparable between ASIR-V50% and VEO®. Conclusion Dealing with CT750HD, despite a significantly longer reconstruction time, the use of VEO® on large patients is of particular interest since it yields to high image quality performances. Lower CTDIvol values are required with the Revolution CT than CT750HD to produce comparable low contrast detectability levels.