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Of all the tracer techniques currently available for the detection of myocardial viability, it is the classic pattern of fluorine-18 deoxyglucose-perfusion mismatch that is clearest from the conceptual point of view and consistently gives good predictive values. Measurements of absolute rates of glucose uptake depend on the much criticized lumped constant, never validated for myocardial ischaemia, and may provide little additional information or may even be confusing because of the bi-directional changes in glucose uptake in response to increasing ischaemia. Labelled nitroimidazole compounds are currently of interest because they are "ischaemia-avid" and because they can be imaged by a gamma camera. Nevertheless, much more work is required to show whether retention of nitroimidazole in ischaemic tissue may reflect viability.

This study describes a non-invasive method for assessment of the lung transit time distribution of a tracer, using first-pass technetium-99m albumin angiocardiography and a model-free method of deconvolution. Ten patients received a first injection of 1 MBq kg-1 in the external jugular vein to position a gamma camera in the left anterior oblique position and two additional injections (5 MBq kg-1) to record first-pass angiocardiographic data. Right and left ventricular time-activity curves were derived from regions of interest every 0.5 s over a 1-min period. The left ventricular curve was deconvoluted by the right ventricular curve to obtain the lung transport function. The deconvolution procedure was based on a modified version of the Kalman filtering technique. The procedure was repeated at an interval of 30 min in eight patients. Two patients were re-examined up to 2 years later. Skewness, kurtosis and relative dispersion of the distributions did not change over time. We also found that the distribution, once normalized by its first moment, was independent of isolated changes in heart rate or cardiac output. Comparison of curve shapes at an interval of 30 min by point by point analysis demonstrated the reproducibility of the technique. We conclude that computation of the pulmonary transit time distribution of 99mTc-albumin from a standard angiocardiography procedure by model-free deconvolution is reliable and reproducible over time. We suggest that it may be a valuable tool for the non-invasive follow-up of the pulmonary circulation.

The use of gamma camera scintigraphy with technetium-99m hexakis-2-methoxyisobutylisonitrile (99mTc-MIBI) for assessment of the response of high-grade osteosarcoma to preoperative chemotherapy was evaluated. Twelve patients with osteosarcoma of the extremities underwent planar examination with 99mTc-MIBI before and after preoperative chemotherapy according to the recommendations of the Scandinavian Sarcoma Group. After calculating a quotient for the tumour and the average activity of both extremities and correcting for background activity, the change in uptake between the two examinations was assessed. This was compared with histological examination of the ultimately resected specimen in 11 patients and progressive clinical disease in one. All the 11 tumours undergoing histological examination showed cellular necrosis of between 50% and 100% as well as a reduced uptake of 99mTc-MIBI, while the single progressive tumour showed an increased uptake. There was a correlation between the reduction of radiopharmaceutical uptake and the histological response in the entire series, while the variation was too large to allow conclusions in individual patients. This variation may have biological reasons or may be due to the planar imaging technique, which only allows semiquantitative evaluation. The technique reflects response to therapy but is not yet clinically applicable for the identification of poor responders, which would serve as a basis for alteration of the chemotherapy regimen. In order to evaluate whether such a role could be fulfilled, further studies using single-photon emission tomography with correction for attenuation and scattering of photons are necessary.

Radiation synovectomy is indicated when conventional pharmacological treatment of chronic synovitis has proved insufficient. In these cases dysprosium-165 ferric hydroxide (DFH) has been demonstrated to be clinically effective. After application of the agent, blood activity measurements and monitoring of activity distribution by gamma camera imaging over the local lymph nodes and the liver are commonly performed for control of possible leakage. In addition, we have used a shadow-shield whole-body counter with a profile facility to evaluate the biokinetics and biodistribution of 165Dy-DFH. Fifteen intra-articular injections were performed in 13 patients who received a median activity of 6.8 GBq (range 0.5-9.9 GBq) 165Dy-DFH. Activity profiles were obtained with the whole-body counter 2, 4 and 6 h after injection of 165Dy-DFH. The doses to non-target organs were calculated using the software MIRDOSE 3. In 10 of 15 treatments, absence of any leakage could be demonstrated. The effect of scattered rays could be observed in 14 measurements. In three patients small amounts of activity could be detected in the urinary bladder and in three patients activity was detected in the local inguinal lymph nodes, while no leakage could be detected by camera imaging. In these cases the individual doses to the bladder were 15 Gy, 65 mGy and 50 mGy, and those to the lymph nodes, 0.54 Gy, 0.89 Gy and 2.41 Gy. The whole-body counter also enabled the monitoring of activity profiles related to more complex pathological structures. In conclusion, using a whole-body counter activity leakage could be detected with much higher sensitivity than by using a gamma camera. The biodistribution of 165Dy-DFH could be determined, and leakage could be localised and related to organs. These results encourage the use of a whole-body counter to identify the site and extent of activity leakage.

Single-tracer methoxyisobutylisonitrile (MIBI) imaging is considered to be a sensitive method for the localization of abnormal parathyroid glands. The aims of this study were to determine which of the analytical techniques described for this method - visual comparison of early (15-min) and late (120-min) images, use of time-activity curves (TACs) generated on regions of interest and factor analysis of dynamic structures (FADS) - corresponds best with surgical findings, and to ascertain the potential overall contribution of presurgical scintigraphy. Fifty-five patients were studied, 34 of whom presented with primary hyperparathyroidism (HPT) and 21 with secondary HPT. After a 925 MBq injection of technetium-99m MIBI, a 40-min dynamic acquisition was performed and static images were acquired at 5, 20, 40 and 120 min using a gamma camera equipped with a pinhole collimator. The dynamic series were submitted to FADS, an attractive non-operator-dependent technique, and TACs were generated on regions of interest after the visual comparison of early and 120-minute images (15'-120'). The presumed localizations of abnormal glands were compared with a sketch drawn by the surgeon. Sensitivity was defined as the percentage of true-positive localizations and was 84.4%, 74% and 65% in adenoma and 76%, 66.6% and 45% in hyperplasia for 15'-120', FADS and TACs, respectively. Surgical accuracy, i.e. the percentage of patients accurately and completely described, was 72%, 56% and 59% in adenoma and 53%, 30% and 22% in hyperplasia for 15'-120', FADS and TACs, respectively. The visual comparison method scored best in all cases. FADS was found to be sensitive in cases of adenoma but was handicapped by more false-positive localizations. TACs were particular inefficient in hyperplasia. With respect to the detection of adenomas, we found a relationship between the gland weight and scintigraphic positivity. This dependence on gland weight was not found in hyperplasia. The poorer results obtained with all techniques for surgical accuracy can be explained by the need for a complete scintigraphic description of all pathological glands found by the surgeon in a patient. This study demonstrates that the 15'-120' visual comparison method is more efficient and less cumbersome than TAC or the attractive FADS technique. However, it was less efficient than neck exploration by an experienced surgeon. Therefore, in our institution, scintigraphic studies are now only requested in selected cases of HPT, usually primary HPT and cases undergoing re-operation.

Gamma camera-based clearance techniques which use the renal uptake ratio (RUR) of the radiotracer are available to estimate the effective renal plasma flow (ERPF) and glomerular filtration rate. To evaluate the accuracy of these techniques, we measured RUR by an optimized procedure and compared it with standard ERPF. Iodine-123 orthoiodohippurate (OIH) scintigraphy and simultaneous para-aminohippurate clearance study for measuring standard ERPF were performed in three hospitals in 24 patients with normal or mildly impaired renal function. 123I-OIH was injected intravenously and 10-s consecutive imaging of the kidneys was started when the abdominal aorta was seen. The attenuation coefficient for 123I was measured in each hospital using the same water-equivalent absorption materials and used for the attenuation correction. After subtracting background radioactivity, RURs were defined as the count ratios of fractional renal uptakes based on the integral from 1 to 2, 2 to 3, 1.5 to 2.5 and 1 to 3 min after the injection of 123I-OIH in relation to injected doses using the following three procedures in respect of attenuation correction: (1) RUR without attenuation correction, (2) RUR with fractional renal uptake corrected by the measured attenuation coefficient, (3) RUR with the total injected dose corrected by the absorption material. To decide upon the appropriate correction method and time interval, RURs were compared with standard ERPF. Among the three correction methods, procedure 2 showed the highest correlation between RUR and standard ERPF, but the correlation coefficient was low (r=0.75). No significant difference was observed among the RURs of each time interval. Individual kidney function measured from early renal uptake may be inaccurate even when appropriate correction is made for attenuation, background activity or time lag between injection and data acquisition. Gamma camera-based measurement of renal function using 123I-OIH is limited with regard to accuracy and reproducibility, though it is convenient and non-invasive.

A study has been undertaken to assess the feasibility of three-dimensional imaging of the dispersion of a non-absorbable tracer released into the colon of normal subjects. Six healthy volunteers were selected who were participating in a scintigraphic study designed to assess the spreading of 1 MBq indium-111 Amberlite resin delivered from a delayed capsule system targeted to release in the ascending colon. In each case subjects were imaged using a rotating gamma camera over a data collection period of approximately 20 min. Three-dimensional volume rendered images demonstrated good visualisation of the dispersion of the tracer throughout the ascending, transverse and descending colon and provided good anatomical visualisation of the shape of the colon, not previously apparent from the planar views. The present study demonstrates for the first time, the successful three-dimensional imaging of a radiolabelled tracer dispersed throughout the colon and opens up the prospects for more detailed study of quantification of the volume and distribution of tracers contained within the colon.

This comparative study was performed to determine whether a conventional planar gamma camera optimised for 511-keV imaging can reliably assess myocardial viability using the fluorine-18 fluorodeoxyglucose (FDG) metabolic tracer previously developed for positron emission tomography (PET). Twenty-seven patients with severe ischaemic cardiomyopathy (mean left ventricular ejection fraction: 20%±9%) having clinically indicated nitrogen-13 ammonia/FDG PET myocardial viability studies consented to resting, four-view, planar myocardial thallium-201 perfusion and FDG metabolism imaging. The resultant PET and planar perfusion/metabolism images (PPI) were independently assessed for FDG defect size and perfusion/metabolism mismatch, using a four-point scale, in each of four vascular regions: apex, circumflex, left anterior and posterior descending coronary artery territories. Of 108 regions, 106 were evaluable (two not assessed by PET). There was complete agreement in 70% of coronary vascular territories, giving an unweighted kappa score of 0.56. Moreover, in 94% of segments agreement was within one grade. Interestingly, six of the seven differences of more than one grade occurred in the circumflex coronary territory, which was also the only region for which planar positron imaging underestimated FDG defect size. Three of four moderate areas of perfusion/metabolism mismatch seen with PET were also seen on PPI. PPI showed three small regions of mismatch not seen on PET, whilst the reverse occurred with one other small region of mismatch. Thus, for this PET protocol, PPI provides very similar information on the extent of regional FDG uptake and occurrence of mismatch. This suggests that perfusion/FDG imaging using an adequately collimated conventional planar gamma camera may be used instead of a formal PET viability study for the clinical detection of viable myocardium, making this form of metabolic assessment more widely available throughout the community.

To test the feasibility of rest first-pass radionuclide angiocardiography (FPRNA) using a 370-MBq (10-mCi) bolus and a single-crystal gamma camera, 40 patients underwent both FPRNA and equilibrium radionuclide angiocardiography (ERNA). Ejection fraction (EF) and regional wall motion (RWM) were assessed by three observers. The interobserver reproducibility was good: the intraclass correlation coefficient was 0.97 for both techniques. The correlation coefficient between FPRNA and ERNA EFs ranged between 0.90 and 0.92. FPRN EFs were significantly higher (P0.003) by less than 5 percentage points, this difference having no clinical implications for patient classification. The study provides arguments as to why this difference may be explained self-attenuation rather than counts statistics problems. Both techniques were concordant for RWM analysis. We conclude that FPRNA with 10 mCi is a reliable tool to assess rest left ventricular function, which makes it possible to perform simultaneously myocardial perfusion and function assessment in a single-day protocol using a single-crystal gamma camera.

Measurement or estimation of the activity of krypton-81m administered to a patient during lung ventilation imaging is difficult, due to the short half-life and continuous delivery via pipework, and no satisfactory method exists. Calculations based on generator activity have the disadvantages that this activity may not be accurately known and that not all activity eluted is inhaled by the patient. The aim of this study was to develop a simple method for estimating the administered activity from the number of counts in each patient image. A formula based on the ratio of counts in 81mKr and technetium-99m lung ventilation and perfusion images was developed and reduced so that administered activity could be directly calculated from the total 81mKr counts, the 99mTc count rate, the administered activity of 99mTc and a constant representing the ratio of counts expected from equal activities of each radioisotope. The formula allows a direct calculation from the image acquisition data following an initial set of experimental work to establish the constant for a particular gamma camera and collimator system.

Six methods of quantifying technetium-99m lung uptake from planar gamma camera images were evaluated. Camera sensitivities, the broad beam attenuation coefficient and build-up factors were derived from suitable phantom measurements. The accuracy of the methods was evaluated by quantifying the lung uptake of 99mTc macroaggregated albumin (MAA) in ten patients and assuming complete trapping by the lung of the known activity of injected MAA particles. Three methods based on published techniques which related the count rate from an image of a lung to that from a lung phantom were the least accurate, producing lung activities which were typically about 70% of the injected activity. Of the other three techniques, the depth-dependent build-up factor method was slightly more accurate than the geometric mean and the depth-independent build-up factor methods, producing average values (+/- SD) of lung activity which were 100% +/- 3%, 106% +/- 3% and 101% +/- 5%, respectively, of the injected activity. To measure lung uptake, all of these latter three methods required an attenuation correction with a flood source transmission scan, and therefore their accuracy was affected by the variation in the activity distribution and attenuation across an image of the thorax.

Attenuation coefficient maps (mu-maps) are a useful way to compensate for non-uniform attenuation when performing single photon emission tomography (SPET). A new method was developed to record single photon transmission data and a mu-map for the brain was produced using a four-head SPET scanner. Transmission data were acquired by a gamma camera opposite to a flood radioactive source attached to one of four gamma cameras in the four-head SPET scanner. Attenuation correction was performed using the iterative expectation maximization algorithm and the mu-map. Phantom studies demonstrated that this method could reconstruct the distribution of radioactivity more accurately than conventional methods, even for a severely non-uniform mu-map, and could improve the quality of SPET images. Clinical application to technetium-99m hexamethyl-propylene amine oxime (HMPAO) brain SPET also demonstrated the usefulness of this method. Thus, this method appears to be promising for improvement in the image quality and quantitative accuracy of brain SPET.

Line-source experiments were conducted to assess the performance of a gamma-camera equipped with a specially designed 511-keV collimator for the planar imaging of positron emitters. The results were compared with the camera performance with routinely used collimators and radionuclides (thallium-201, technetium-99m and gallium-67). With positron emitters, scatter contributed less to the widening of the line spread function than with radionuclides emitting lower photon energies. These observations can be explained by the relative deterioration in the discrimination power of the gamma-camera to reject scattered radiation at low energies. Planar 511-keV imaging may provide relevant clinical information, as we showed by fluorodeoxyglucose studies in a patient with a myocardial infarction and in a patient with a malignant lymphoma. It is concluded that positron emitters can be effectively applied for planar imaging with the generally available gamma-cameras. This study implies that radiotracers developed for positron emission tomography may find a place in the practice of conventional nuclear medicine.

Gallium 67 scanning in the malignant lympho mas has been done, with variable success, for over 20 years. After initial enthusiasm, the technique fell into disrepute and it was not until the early 1980s that it enjoyed a revival. There have been many major contributions to the literature, both favourable and unfavourable. The reasons for the latter include: poor instrumentation (only single-pulse height analysis), low gallium 67 doses, impatient and careless scanning techniques, timing of the study after treatment (chemotherapy, radiation) and insensitive methods of confirmation of the presence or absence of disease (“truth”). Anatomical diagnostic techniques (computed tomography, plain X-radiography, magnetic resonance imaging and others) are incapable of distinguishing viable tumour in normal size lymph nodes or necrotic/fibrotic residual masses. With improvements in instrumentation (triple-pulse height analysis, gamma camera resolution and tomographic techniques) gallium 67 can detect active tumour in residual masses and in normal-size nodes. This is due to gallium 67's unique ability to localize in viable tumour cells. It has greater than 90% sensitivity, specificity, accuracy and positive predictive value in patients with lymphoma. Its major contributions are in: staging (changing management of mediastinal disease, obviating the need for a laparotomy and clearlyidentifying stage IV disease); detecting relapse or residual, progressive disease (it establishes true complete remission and is often the first and only evidence of relapse before clinical evidence); predicting response to therapy (failure to convert to a negative scan post-treatment signals a poor prognosis and alternative therapy is required); and predicting outcome — prognosis (it is the only diagnostic modality to predict outcome accurately).

The aim of this study was to evaluate a method for quantification of inhomogeneity in ventilation single-photon emission tomography (SPET). Nine emphysematous patients, nine life-long non-smokers and nine smokers were included in the study. The SPET investigation was performed after 50 MBq (99m)Tc-Technegas had been inhaled by each subject in the supine position. A single-head gamma camera, equipped with a general-purpose parallel-hole collimator using 64 projections (20 s each) over 360 degrees, was used. Data were acquired in 128x128 matrices. Attenuation correction was applied based upon computed tomography (CT) density maps. Lung regions of interest were delineated manually on CT images and then positioned on SPET images. Several attenuation-corrected transaxial SPET slices (thickness 1 cm, spacing 3.5 cm) were reconstructed. Each SPET slice was divided into several 2x2x1 cm(3) elements. Inhomogeneity was assessed by the coefficient of variation (CV) of the pixel counts within these elements (micro-level) and the CV of the total counts of the elements (macro-level). Micro-level CVs in non-smokers varied between 1% and 41%, whereas they were dispersed over a wide range (1%-600%) in emphysematous patients. In seven smokers, the frequency distribution of micro-level CVs was within the normal range, whereas in the other two smokers the values were between the normal range and the range in emphysematous patients. The pooled mean values of micro-level CVs and macro-level CVs in each subject clearly separated the patients from the others. Parametric images of micro-level CV indicated the localisation and severity of ventilation inhomogeneity. We conclude that the present method enables quantification and localisation of regional inhomogeneity in ventilation SPET images.

Planar gamma camera scintigraphy is a well-established technique for characterising the deposition and clearance of radiolabelled aerosols. While single-photon emission tomography (SPET) can offer superior assessment of radioaerosol deposition and better differentiation between peripheral and central deposition, the long acquisition times of single-headed SPET have largely prevented its use for measuring clearance or deposition of fast-clearing radioaerosols. This study investigated the feasibility of fast dynamic SPET imaging (1 min/frame) using a three-headed gamma camera to assess the regional and total deposition and clearance of different radioaerosols over a period of 26 min. Six subjects inhaled nebulised technetium-99m diethylene triamine penta-acetic acid radiolabelled aerosols with small and large droplet sizes [mass median aerodynamic diameter (MMAD) 3.2 +/- 0.2 and 6.5 +/- 0.2 microm, span 1.8 and 1.7, respectively] and in normal (0.9%) or hypertonic (7%) saline with controlled breathing on four separate occasions. The penetration indices (PIs) calculated from the SPET data for normal saline were 0.50 +/- 0.04 and 0.36 +/- 0.02 for the small and large droplet sizes, respectively. Consistent with the hygroscopic growth of the hypertonic aerosols, the PIs for hypertonic saline were lower, at 0.43 +/- 0.02 and 0.34 +/- 0.02 for the small and large droplet sizes, respectively. PIs calculated from the planar data showed similar trends, but failed to detect the significant difference seen with SPET between small normal and small hypertonic saline radioaerosols. In conclusion, the feasibility of using fast dynamic SPET for imaging radioaerosol deposition and associated radiolabel clearance in the lung has been successfully demonstrated. The fast SPET was able to reveal important differences in aerosol deposition that were not detected by planar imaging.

Positron emission tomography (PET) has evolved into a technique that can accurately determine the distribution of positron-emitting radionuclides. The addition of a coincidence detection mode to a standard dual-head detector system has resulted in the option of single-photon and annihilation coincidence detection. This new device for imaging fluorine-18 2-fluoro-2-deoxy-D-glucose ((18)F-FDG) accumulation in neoplasms became commercially available in 1994. Besides conventional low-energy imaging in the collimated single-photon mode, it offers a relatively inexpensive opportunity to perform uncollimated PET by switching to the coincidence acquisition mode. This review summarises the clinical value of (18)F-FDG detection with a dual-head coincidence camera in oncology. The results are compared with the overall results obtained using dedicated PET scanners. With respect to head and neck tumours, (18)F-FDG coincidence mode gamma camera imaging (CGI) yields results that are in agreement with those obtained with dedicated PET scanners. With regard to other malignancies, such as lung cancer, lymphoma and brain tumours, data in the literature are too scarce to draw any definite conclusions. In general, the results of (18)F-FDG CGI in tumours15 mm seem to be comparable to those obtained with dedicated PET scanners, whereas in tumours15 mm, the relative sensitivity of (18)F-FDG CGI is approximately 80%. Using attenuation correction, the diagnostic yield of (18)F-FDG CGI may increase. However, further clinical investigation is required to definitely establish its value in staging primary disease, therapy monitoring and assessment of tumour recurrence in clinical oncology.

A stereotactic, normal perfusion database is imperative for optimal clinical brain single-photon emission tomography (SPET). However, interdepartmental use of normal data necessitates accurate transferability of these data sets. The aim of this study was to investigate transfer of three normal perfusion databases obtained in the same large population of healthy volunteers who underwent sequential scanning using multihead gamma cameras with different resolution. Eighty-nine healthy adults (46 females, 43 males; aged 20-81 years) were thoroughly screened by history, biochemistry, physical and full neurological examination, neuropsychological testing and magnetic resonance imaging. After injection of 925 MBq technetium-99m labelled ethyl cysteinate dimer (ECD) under standard conditions, 101 scans were acquired from all subjects (12 repeat studies) on a triple-head Toshiba GCA-9300A (measured average FWHM 8.1 mm). Ninety-one sequential scans were performed on a dual-head Elscint Helix camera (FWHM 9.6 mm) and 22 subjects also underwent imaging on a triple-head Prism 3000 (FWHM 9.6 mm). Images were transferred to the same processing platform and reconstructed by filtered back-projection with the same Butterworth filter (order 8, cut-off 0.9 cycles/cm) and uniform Sorensen attenuation correction (mu = 0.09). After automated rigid intrasubject registration, all subjects were automatically reoriented to a stereotactic template by a nine-parameter affine transformation. The databases were analysed using 35 predefined volumes of interest (VOIs) with normalisation on total VOI counts. For comparison, the high-resolution data were smoothed with a 3D Gaussian kernel to achieve more similar spatial resolution. Hoffman phantom measurements were conducted on all cameras. Partial volume effects after smoothing varied between -6.5% and 10%, depending on VOI size. Between-camera reproducibility was 2.5% and 2.7% for the Toshiba camera versus the Helix and the Prism database, respectively. The highest reduction in between-camera variability was achieved by resolution adjustment in combination with linear washout correction and a Hoffman phantom-based correction. In conclusion, transfer of normal perfusion data between multihead gamma cameras can be accurately achieved, thereby enabling widespread interdepartmental use, which is likely to have a positive impact on the diagnostic capabilities of clinical brain perfusion SPET.

This study assessed a dual-head coincidence gamma camera (hybrid PET) equipped with single-photon transmission for myocardial fluorine-18 fluorodeoxyglucose (FDG) imaging by comparing this technique with conventional positron emission tomography (PET) using a dedicated ring PET scanner. Twenty-one patients were studied with dedicated FDG ring PET and FDG hybrid PET for evaluation of myocardial glucose metabolism, as well as technetium-99m tetrofosmin single-photon emission tomography (SPET) to estimate myocardial perfusion. All patients underwent transmitted attenuation correction using germanium-68 rod sources for ring PET and caesium-137 point sources for hybrid PET. Ring PET and hybrid PET emission scans were started 61+/-12 and 98+/-15 min, respectively, after administration of 154+/-31 MBq FDG. Attenuation-corrected images were reconstructed iteratively for ring PET and hybrid PET (ac-hybrid PET), and non-attenuation-corrected images for hybrid PET (non-ac-hybrid PET) only. Tracer distribution was analysed semiquantitatively using a volumetric vector sampling method dividing the left ventricular wall into 13 segments. FDG distribution in non-ac-hybrid PET and ring PET correlated with r=0.36 (P0.0001), and in ac-hybrid PET and ring PET with r=0.79 (P0.0001). Non-ac-hybrid PET significantly overestimated FDG uptake in the apical and supra-apical segments, and underestimated FDG uptake in the remaining segments, with the exception of one lateral segment. Ac-hybrid PET significantly overestimated FDG uptake in the apical segment, and underestimated FDG uptake in only three posteroseptal segments. A three-grade score was used to classify diagnosis of viability by FDG PET in 136 segments with reduced perfusion as assessed by SPET. Compared with ring PET, non-ac-hybrid PET showed concordant diagnoses in 80 segments (59%) and ac-hybrid PET in 101 segments (74%) (P0.001). Agreement between ring PET and non-ac-hybrid PET was best in the basal lateral wall and in the apical-septal segment (80%-100%), and lowest in the apical, supra-apical and posteroseptal segments (41%-55%). Ac-hybrid PET showed highest agreement in the lateral wall (89%-100%), and lowest agreement in the apical and the basal septal segments (59%-67%). In conclusion, non-uniform attenuation correction with singles transmission significantly improves the diagnostic accuracy of myocardial dual-head gamma camera coincidence imaging with FDG. However, results equivalent to those obtained with ring PET cannot yet be attained, even if attenuation correction is applied. New rebinning algorithms for three-dimensional data may further improve the performance of ac-hybrid PET and should be evaluated in future studies.

Filtered back-projection (FBP) is generally used as the reconstruction method for single-photon emission tomography although it produces noisy images with apparent streak artefacts. It is possible to improve the image quality by using an algorithm with iterative correction steps. The iterative reconstruction technique also has an additional benefit in that computation of attenuation correction can be included in the process. A commonly used iterative method, maximum-likelihood expectation maximisation (ML-EM), can be accelerated using ordered subsets (OS-EM). We have applied to the OS-EM algorithm a Bayesian one-step late correction method utilising median root prior (MRP). Methodological comparison was performed by means of measurements obtained with a brain perfusion phantom and using patient data. The aim of this work was to quantitate the accuracy of iterative reconstruction with scatter and non-uniform attenuation corrections and post-filtering in SPET brain perfusion imaging. SPET imaging was performed using a triple-head gamma camera with fan-beam collimators. Transmission and emission scans were acquired simultaneously. The brain phantom used was a high-resolution three-dimensional anthropomorphic JB003 phantom. Patient studies were performed in ten chronic pain syndrome patients. The images were reconstructed using conventional FBP and iterative OS-EM and MRP techniques including scatter and non-uniform attenuation corrections. Iterative reconstructions were individually post-filtered. The quantitative results obtained with the brain perfusion phantom were compared with the known actual contrast ratios. The calculated difference from the true values was largest with the FBP method; iteratively reconstructed images proved closer to the reality. Similar findings were obtained in the patient studies. The plain OS-EM method improved the contrast whereas in the case of the MRP technique the improvement in contrast was not so evident with post-filtering.

Lateral attenuation in single-photon emission tomography (SPET) myocardial perfusion imaging (MPI) has been attributed to the left arm if it is held by the patient's side during data acquisition. As a result MPI data are conventionally acquired with the arms held above the head. The aims of this study were to determine the effect of imaging arms down on reconstructed tomographic images depicting regional myocardial thallium-201 distribution and to assess whether attenuation-corrected (AC) myocardial perfusion images acquired arms down could replace uncorrected (NC) images acquired arms up for routine clinical service. Twenty-eight patients referred for routine MPI underwent sequential 180 degrees emission/transmission imaging for attenuation correction using an L-shaped dual-headed gamma camera (GE Optima) fitted with two gadolinium-153 scanning line sources. Delay data were acquired twice: once supine with the arms up and then supine with the arms down. Detector radius of rotation (ROR) for arms up and arms-down studies was recorded. For each data set, count density was measured in 17 segments of a polar plot and segmental uptake expressed relative to study maximum. Oblique images were assessed qualitatively by two observers blinded to study type for tracer distribution and overall quality. Transmission maps were assessed for truncation. Mean detector ROR was 190 mm for arms-up studies and 232 mm for arms-down studies (P0.05). Population mean segmental relative uptake values for NC arms-up studies were higher than for NC arms-down studies, with the greatest difference seen anterolaterally. Nevertheless, the majority (24/28) of oblique NC arms-up and NC arms-down images appeared similar and only four (14%) NC arms-down studies showed additional areas of reduced count density (one anterior and three lateral). Corresponding AC arms-down studies showed that count density within the anterior defect improved to normal but the lateral reductions persisted, and in two of these three studies the arms-down transmission map was distorted. Population mean segmental relative uptake values for NC arms-down studies were lower than for AC arms-down studies apart from three anterolateral segments where NC arms-down values were higher. Of 28 AC arms-down studies, 11 (39%) were of reduced quality compared with NC arms-up studies because of poorer spatial resolution and because AC enhances liver activity compared with NC. It is concluded that arm positioning influences reconstructed tomographic images depicting regional 201T1 distribution, particularly anterolaterally. There is lateral undercorrection in approximately 10% of AC arms-down studies, possibly because of attenuation map truncation. Image quality is reduced in about one-third of AC armsdown studies compared with NC arms-up studies. These data suggest that this attenuation correction method is not sufficiently robust to allow routine acquisition of MPI data with the arms down.

Dual-headed gamma cameras with coincidence detection (MCD) are increasingly used for imaging of positron-emitting tracers, such as fluorine-18 fluorodeoxyglucose (FDG). In this study, we examined differences between FDG MCD and FDG positron emission tomography (PET) as the gold standard to determine whether FDG MCD could be used for assessment of myocardial viability in daily practice. Nineteen patients with a previous myocardial infarction (17 men; mean left ventricular ejection fraction 44%+/-13%) underwent FDG MCD, FDG PET, resting echocardiography and technetium-99m tetrofosmin gated single-photon emission tomography (SPET). At the 50% threshold value for FDG PET, the area under the receiver operating characteristic curve for FDG MCD was 0.77+/-0.03. In 107 dyssynergic segments on echocardiography and 151 segments with hypoperfusion on 99mTc-tetrofosmin SPET, the specificity of FDG MCD for the detection of myocardial viability was 72% and 76% respectively, with a sensitivity of 69% and 72% respectively. Regional analysis showed a significantly lower agreement of FDG MCD and FDG PET in the inferior and septal regions (58% for dyssynergic segments and 65% for segments with hypoperfusion), as compared with the other regions (85% for dyssynergic regions, P0.05, and 86% for segments with hypoperfusion, P0.05). Five patients (26%), who all had a body mass indexor =25% kg/m2, showed more than 25% disagreement between FDG MCD and FDG PET. Because of the moderate overall agreement with FDG PET, the low sensitivity in akinetic or dyskinetic regions and the low agreement in the inferior and septal regions, further studies and implementations of technical developments are needed before FDG MCD can be introduced into clinical practice for the assessment of myocardial viability.

The purpose of this study was to assess the value of technetium-99m methoxyisobutylisonitrile (MIBI) single-photon emission tomography (SPET) and an iterative reconstruction algorithm for the preoperative localisation of parathyroid adenomas (PTAs). Seventy-two patients (26 male, 46 female, mean age 58+/-16 years) with known primary hyperparathyroidism were examined preoperatively. First, a thyroid examination was performed to detect possible MIBI-accumulating thyroid lesions. Planar scans were then acquired 15 and 120 min and tomographic images 120 min after intravenous injection of 740 MBq 99mTc-MIBI, using a triple-head gamma camera (Picker Prism 3000). Additionally, 99mTc-MIBI/ 99mTc-pertechnetate subtraction scintigraphy of the early planar images was performed. The SPET data were evaluated using an iterative reconstruction (multiplicative iterative SPET reconstruction: MISR) as well as a standard algorithm (FBP: filtered back-projection with application of a 3-D low-pass postfilter). The weight of the resected PTAs ranged from 110 mg to 5 g. Using planar MIBI scans, correct localisation of the side of the PTA was possible in 81% of cases (58% for PTAs weighing less than 500 mg). Sensitivity increased to 94% using SPET and FBP, while with MISR it rose further, to 97%. Patients with PTAs weighing less than 500 mg showed a sensitivity of 88% with MISR and 81% with FBP. Furthermore, there was a clear improvement in image quality using MISR. None of the normal parathyroid glands were visualised. This study indicates that, in comparison with planar scintigraphy, 99mTc-MIBI SPET is a more sensitive and specific tool for topographical localisation of PTAs, especially those that are small. There is a further improvement in sensitivity and image quality when iterative reconstruction is used instead of FBP.

The main disadvantage of technetium-99m methoxyisobutylisonitrile (MIBI) prone scintimammography is its limited sensitivity for T1a and T1b cancers with a size of less than 1 cm. We have developed a high-resolution scintimammographic technique using a gamma camera based on a new concept, namely a position-sensitive photo-multiplier tube. The field of view of this camera, previously known as the SPEM (single photon emission mammography) camera, was 10 cm diameter. Scintimammographic images were acquired in the axial view; each breast was compressed to a thickness of 3-6 cm, modal class 4 cm. When the compressed breast was larger than the field of view, more than one study was performed in order to image the entire gland. Fifty-three patients were studied with high-resolution-scintimammography (HRSM) and Anger camera prone scintimammography (ACPSM). HRSM was performed 70 min after i.v. administration of 740 Mbq of (99m)Tc-MIBI; ACPSM images were acquired 10 and 60 min following the injection. Early 10-min ACPSM images were only evaluated for routine diagnostic purposes, while comparison was carried out between the 60-min ACPSM and 70-min HRSM images. At fine-needle aspiration (FNA) and/or open biopsy, 31 patients showed cancer: 15 T1c, 11 T1b and 5 T1a. In T1a-T1b cancers, the sensitivity of scintimammography was 50% with ACPSM and 81.2% with HRSM (P0.01). Specificity was 86% with both techniques. HRSM is a promising new technique that improves the sensitivity of (99m)Tc-MIBI scintimammography in tumours sized less than 1 cm without apparently reducing its specificity. We are now working on a larger field-of-view camera.

Using iodine-123 labelled radiotracers, the presence of 2.5% high-energy photons causes image deterioration due to increased scatter. To investigate the influence of these photons on image quality, we measured the spectrum of 123I with a medium-energy (ME), a low-energy all-purpose (LEAP) and a low-energy high-resolution (LEHR) collimator. Even in air, using low-energy collimators a high baseline activity was observed over the total energy detection range of the gamma camera. The 159-keV photopeak to scatter activity ratio fell from 5.9 for ME to 3.6 and 2.9 for LE collimators. Acquisition of images with LEHR collimators with energy windows set at 159 keV and 500 keV demonstrated that the 159-keV LEHR image is a combination of the ME image of the object and of the LEHR 500-keV image. Because of their important septal penetration and greater geometric detection efficiency compared with the 159-keV photons of 123I, the contribution of high-energy photons is dependent on the source-detector distance. For a small source placed in air, the scatter to photopeak activities varied from 17.4% at 80 cm to 37.8% at 5 cm distance from an LEHR collimator. Considering only the scatter problem, ME collimators are the best choice for 123I studies. When using LE collimators for high-resolution tomography with 123I-labelled compounds, scatter contribution from high-energy photons has to be corrected for quantitative analysis or when dual-isotope studies are performed, whether or not these studies are acquired simultaneously.

The purpose of this study was to compare the diagnostic accuracy of fluorine-18 fluorodeoxyglucose (FDG) images obtained with (a) a dual-head coincidence gamma camera (DHC) equipped with 5/8-inch-thick NaI(Tl) crystals and parallel slit collimators and (b) a dedicated positron emission tomograph (PET) in a series of 28 patients with known or suspected malignancies. Twenty-eight patients with known or suspected malignancies underwent whole-body FDG PET imaging (Siemens, ECAT 933) after injection of approximately 10 mCi of 18F-FDG. FDG DHC images were then acquired for 30 min over the regions of interest using a dual-head gamma camera (VariCam, Elscint). The images were reconstructed in the normal mode, using photopeak/photopeak, photopeak/Compton, and Compton/photopeak coincidence events. FDG PET imaging found 45 lesions ranging in size from 1 cm to 7 cm in 28 patients. FDG DHC imaging detected 35/45 (78%) of these lesions. Among the ten lesions not seen with FDG DHC imaging, eight were less than 1.5 cm in size, and two were located centrally within the abdomen suffering from marked attenuation effects. The lesions were classified into three categories: thorax (n=24), liver (n=12), and extrahepatic abdominal (n=9). FDG DHC imaging identified 100% of lesions above 1.5 cm in the thorax group and 78% of those below 1.5 cm, for an overall total of 83%. FDG DHC imaging identified 100% of lesions above 1.5 cm, in the liver and 43% of lesions below 1.5 cm, for an overall total of 67%. FDG DHC imaging identified 78% of lesions above 1.5 cm in the extrahepatic abdominal group. There were no lesions below 1.5 cm in this group. FDG coincidence imaging using a dual-head gamma camera detected 90% of lesions greater than 1.5 cm. These data suggest that DHC imaging can be used clinically in well-defined diagnostic situations to differentiate benign from malignant lesions.

The characteristic whole-body and pinhole scintigraphic manifestations of osteo-enthesopathy and arthropathy in Reiter's syndrome (RS) are described, with an emphasis on early diagnosis. We analysed 59 sets of whole-body and pinhole bone scintigrams of 59 patients with RS. The population comprised 47 men and 12 women with an age range from 15 to 53 years (mean=29.4). Bone scintigraphy was carried out 2-2.5 h after intravenous injection of technetium-99m hydroxydiphosphonate using a single-head gamma camera (Siemens Orbiter Model 6601) with a low-energy high-resolution and a 4-mm pinhole collimator for whole-body and pinhole scintigraphy, respectively. In total 262 lesions of osteo-enthesopathy and arthritis were detected on 59 whole-body scintigrams, an incidence of 4.4 lesions per patient. As anticipated, the lesional distribution was asymmetrical: 68% were in the lower limb skeleton and 32% in the axial and upper limb skeleton. Pinhole bone scintigraphy, applied selectively to one region of interest in each case, enabled us to accurately diagnose arthritis and osteo-enthesopathy. It was noteworthy that osteo-enthesopathy, alone or in combination with arthritis, occurred in 78.9%, and had a strong predilection for the foot bones, especially the calcaneus (25. 6%). Pinhole scintigraphy detected enthesopathy in the absence of radiographic alteration in 14.1% of cases and portrayed characteristic signs of RS in 6.9%. Whole-body bone scintigraphy augmented with pinhole scintigraphy was found to be useful in order to panoramically display the systemic involvement pattern, to assess the characteristic bone and articular alterations and to detect early signs of RS.

Melanin synthesised in melanoma cells presents a unique target to which the treatment can be selectively addressed, provided the pigment is recognised by a suitable drug. Methylene blue (MTB) possesses a high affinity for melanin and, therefore, accumulates preferentially in melanoma cells. Since not directly toxic to the tumour, MTB serves as a carrier for radioisotopes and, once taken up by melanoma cells, acts as a selectively localised source of radiation. Hence, radioderivatives of the compound can be used for both diagnosis and therapy of disseminated melanoma. Eleven patients with confirmed metastatic melanoma and one with a recent local recurrence were studied using radioiodinated (iodine-123 or iodine-131) MTB and a gamma camera. Biopsies of cutaneous lesions were taken to determine directly the compound uptake in tumours. This first clinical investigation concerning the diagnostic potential of radioiodinated MTB in patients with disseminated melanoma confirmed the existence of approximately 80% of internal lesions previously identified by routine methods and, additionally, enabled detection of unknown secondaries in 6 of 12 patients studied. There were no false-positive gamma camera images regardless of whether 123I or 131I was used. 131I proved to be more suitable than 123I for detecting melanoma metastases with radioiodinated MTB. Hazy images of the lesions treated with external beam radiation and/or some drugs suggest that initial radio- and chemotherapy might affect MTB uptake in melanoma metastases and reduce the clarity of the scintigrams obtained from a gamma camera. However, small, untreated internal lesions that cannot be visualised easily with the standard diagnostic methods are revealed with 131I-MTB regardless of their localisation. It is concluded that use of radioiodinated MTB in conjunction with gamma camera or positron emission tomographic imaging might prove to be a useful and accessible tool for the detection of early melanoma dissemination.

Deadtime count loss may cause significant errors in quantitative measurements performed by scintigraphic techniques. Deadtime depends on the scattering condition, and may vary among patients. The aim of this study was to estimate deadtime in imaging a human subject. A cylindrical phantom filled with various concentrations of technetium-99m solution was imaged with a gamma camera, and deadtime was assessed assuming the gamma camera to be a non-paralysable system (multi-dose method). Deadtime for the cylindrical phantom was also estimated using a point source to monitor counting efficiency (reference source method). Radionuclide angiography of the chest was performed in 38 patients with a reference source in the field of view, and temporal changes in count loss were assessed. The deadtime for each patient was calculated by the reference source method. The deadtime for the cylindrical phantom was estimated as 6.96+/-0.09 micros by the reference source method and was almost identical to that obtained by the multi-dose method (6.93 micros). Deadtime ranged from 6.01 to 9.58 micros in radionuclide angiography, and was positively correlated with the ratio of body weight in kg to body height in cm (y=8.566 x+5.611, r=0.869). Count loss was successfully corrected using the deadtime predicted with the regression line. In summary, the deadtime in imaging a human subject has a wide range and is related to the constitution of the subject. Correction for count loss using a deadtime predicted for each patient may be helpful in improving the reliability of quantitative nuclear medicine.

Short acquisition protocols for gated single-photon emission tomography (SPET) myocardial perfusion imaging are desirable for sequential imaging to evaluate the myocardial response during pharmacological intervention. In this study a less than 5 min gated SPET acquisition protocol is proposed. Perfusion characteristics (defect severity) and left ventricular ejection fraction (LVEF), end-diastolic and end-systolic volumes (EDV, ESV), wall motion (WM) and wall thickening (WT) were calculated, checked for reproducibility and compared with data obtained using a standard gated SPET acquisition protocol. Gated SPET images were recorded in 20 patients starting 60 min after the administration of 925 MBq technetium-99m tetrofosmin at rest. The 5 min gated SPET studies were acquired with a three-head camera equipped with Cardiofocal collimators. This protocol was repeated twice. In addition gated SPET studies were acquired according to a standard protocol using parallel-hole collimators. The severity of perfusion defects was quantified on polar maps using the non-gated image data and a normal database. LVEF, EDV, ESV, WM and WT were calculated from the gated images. The agreement between 5-min and standard gated SPET acquisitions was excellent for all investigated parameters. The reproducibility of repeated 5-min acquisitions for the quantification of perfusion defect severity was excellent (r=0.97). The agreement for segmental WT scores between repeated 5-min gated SPET acquisitions was good: kappa=0.71; major differences in segmental classification were observed in 2.5%. For WM a good agreement was found for segments with a tracer uptake >/=30% of the maximum: kappa=0.65, major differences =7.7%. Excellent reproducibility was found for LVEF, EDV and ESV measurements: r=0.97, 0.99 and 0.99, respectively. It is concluded that fast gated SPET perfusion studies acquired in less than 5 min yield accurate and reproducible measurements of myocardial perfusion and function (global and regional). In addition the results obtained with the 5-min gated SPET protocol correlate well with those obtained using a standard acquisition protocol.

A practical method for scatter and attenuation compensation was employed in thallium-201 myocardial single-photon emission tomography (SPET or ECT) with the triple-energy-window (TEW) technique and an iterative attenuation correction method by using a measured attenuation map. The map was reconstructed from technetium-99m transmission CT (TCT) data. A dual-headed SPET gamma camera system equipped with parallel-hole collimators was used for ECT/TCT data acquisition and a new type of external source named ”sheet line source” was designed for TCT data acquisition. This sheet line source was composed of a narrow long fluoroplastic tube embedded in a rectangular acrylic board. After injection of 99mTc solution into the tube by an automatic injector, the board was attached in front of the collimator surface of one of the two detectors. After acquiring emission and transmission data separately or simultaneously, we eliminated scattered photons in the transmission and emission data with the TEW method, and reconstructed both images. Then, the effect of attenuation in the scatter-corrected ECT images was compensated with Chang’s iterative method by using measured attenuation maps. Our method was validated by several phantom studies and clinical cardiac studies. The method offered improved homogeneity in distribution of myocardial activity and accurate measurements of myocardial tracer uptake. We conclude that the above correction method is feasible because a new type of 99mTc external source may not produce truncation in TCT images and is cost-effective and easy to prepare in clinical situations.

Measurement of absolute renal function by gamma camera techniques requires knowledge of kidney depth to correct for soft tissue attenuation, there is debate about the need to take depth into account when only relative renal function is estimated. The aim of this study was to derive a formula for renal depth in children and to assess the importance of depth correction when relative renal function is assessed with dimercaptosuccinic acid (DMSA) on the gamma camera. In this study, kidney depths were derived from measurements on abdominal computerised tomography (CT) images in 57 children in the supine position with two normally located kidneys. Using best-subset regression analysis, one formula for both left and right kidney depth (KD, cm) was developed based on the easily measured parameters of height (H, cm) and body weight (W, kg). The inclusion of extra variables was found to significantly improve the model compared with a model using weight alone (P

Cardiofocal collimators (CFCs) are more sensitive than parallel-hole collimators (PHCs) of the same resolution because the rays converge in the centre of the field of view. After reconstruction a useful field of view with a 10 cm radius in which both sensitivity and resolution are homogeneous is obtained. In this article the feasibility and accuracy of gated single-photon emission tomographic (gated SPET) myocardial perfusion imaging using a triple-head camera equipped with CFC, is evaluated. Twenty patients with a history of myocardial infarction were studied. SPET myocardial perfusion images, gated in eight time bins, were acquired in a random sequence with a PHC and a CFC for each patient. Imaging was started 60 min after the injection of 925 MBq of technetium-99m tetrofosmin at rest. Ninety-six projections over 360 degrees were acquired, with 32 stops of 40 s for the PHC and 20 s for the CFC in order to obtain similar count densities. The extent (EXT) and severity (SEV) of perfusion defects were quantified on polar maps using the non-gated data. Left ventricular volumes [end-diastolic volume (EDV), end-systolic volume (ESV)] and ejection fraction (LVEF) were calculated from gated data using the Cedars-Sinai program. In 17 of 20 patients the complete left ventricle was positioned within the useful field of view of the CFC. The results in respect of perfusion, volumes and ejection fraction were almost identical to those obtained with the PHC. The mean difference+/-SD between the CFC and the PHC was -2.30+/-7.16 (% of LV area) for EXT, -0.48+/-2.90 for SEV (arbitrary units), -1,50+/-5.25 (ml) for EDV and 0.53+/-4.10 (%) for LVEF. The largest differences in EXT and LV volumes were observed in patients in whom a part of the LV was not positioned within the useful field of view. We conclude that, for the majority of patients, identical information with regard to both perfusion and function can be derived from gated SPET myocardial perfusion studies obtained with PHCs or with CFCs. Because of the greater sensitivity, however, a much shorter acquisition time is required with CFCs.

Deadtime count loss may cause error in quantitative measurements with a gamma camera. We evaluated the effect of deadtime loss on the measurement of cerebral blood flow (CBF). Radionuclide angiography with technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO) was performed in 20 patients. A reference source was placed on the periphery of the detector to monitor deadtime loss, and CBF was calculated based on the data of radionuclide angiography with and without deadtime correction. In ten patients injected with 1110 MBq of the tracer, the CBF value without correction was 9.9%+/-1.8% higher than that with correction. This shows that deadtime loss may cause significant overestimation. The difference between CBF values obtained with and without correction was smaller in ten patients with an injected dose of 370 MBq (3.0%+/-1.2%). These results suggest a substantial effect of deadtime loss on CBF as measured by radionuclide angiography and 99mTc-HMPAO.

The aim of this study was to optimise the parameters affecting the Bremsstrahlung scintigraphy of patients injected with strontium-89 chloride. The parameters considered were : (1) instrumental detection efficiency, and (2) tissue attenuation factor for 89Sr calibrated sources, which permit quantitative evaluation of the activity in a given bone lesion. Some typical examples of in vivo 89Sr imaging are presented to illustrate the clinical utility of the imaging procedure developed by us, which is implemented in our department for all patients treated with 89Sr chloride.

The purpose of this study was to determine whether data acquisition in the list mode and iterative tomographic reconstruction would render feasible cardiac phase-synchronized thallium-201 single-photon emission tomography (SPET) of the myocardium under routine conditions without modifications in tracer dose, acquisition time, or number of steps of the a gamma camera. Seventy non-selected patients underwent 201T1 SPET imaging according to a routine protocol (74 MBq/2 mCi 201T1, 180 degrees rotation of the gamma camera, 32 steps, 30 min). Gamma camera data, ECG, and a time signal were recorded in list mode. The cardiac cycle was divided into eight phases, the end-diastolic phase encompassing the QRS complex, and the end-systolic phase the T wave. Both phase- and non-phase-synchronized tomograms based on the same list mode data were reconstructed iteratively. Phase-synchronized and non-synchronized images were compared. Patients were divided into two groups depending on whether or not coronary artery disease had been definitely diagnosed prior to SPET imaging. The numbers of patients in both groups demonstrating defects visible on the phase-synchronized but not on the non-synchronized images were compared. It was found that both postexercise and redistribution phase tomograms were suited for interpretation. The changes from end-diastolic to end-systolic images allowed a comparative assessment of regional wall motility and tracer uptake. End-diastolic tomograms provided the best definition of defects. Additional defects not apparent on non-synchronized images were visible in 40 patients, six of whom did not show any defect on the non-synchronized images. Of 42 patients in whom coronary artery disease had been definitely diagnosed, 19 had additional defects not visible on the non-synchronized images, in comparison to 21 of 28 in whom coronary artery disease was suspected (P0.02; chi 2). It is concluded that cardiac phase-synchronized 201T1 SPET of the myocardium was made feasible by list mode data acquisition and iterative reconstruction. The additional findings on the phase-synchronized tomograms, not visible on the non-synchronized ones, represented genuine defects. Cardiac phase-synchronized 201T1 SPET is advantageous in allowing simultaneous assessment of regional wall motion and tracer uptake, and in visualizing smaller defects.

Advances in fully three-dimensional (3D) image reconstruction techniques have permitted the development of a commercial, rotating, partial ring, fully 3D positron emission tomographic (PET) scanner, the ECAT ART. The system has less than one-half the number of bismuth germanate detectors compared with a full ring scanner with the equivalent field of view, resulting in reduced capital cost. The performance characteristics, implications for installation in a nuclear medicine department, and clinical utility of the scanner are presented in this report. The sensitivity (20 cm diameterx20 cm long cylindrical phantom, no scatter correction) is 11400 cps.kBq-1.ml-1. This compares with 5800 and 40500 cps.kBq-1.ml-1 in 2D and 3D respectively for the equivalent full ring scanner (ECAT EXACT). With an energy window of 350-650 keV the maximum noise equivalent count (NEC) rate was 27 kcps at a radioactivity concentration of approximately 15 kBq.ml-1 in the cylinder. Spatial resolution is approximately 6 mm full width at half maximum on axis degrading to just under 8 mm at a distance of 20 cm off axis. Installation and use within the nuclear medicine department does not appreciably increase background levels of radiation on gamma cameras in adjacent rooms and the dose rate to an operator in the same room is 2 microSv. h-1 for a typical fluorine-18 fluorodeoxyglucose (18F-FDG) study with an initial injected activity of 370 MBq. The scanner has been used for clinical imaging with18F-FDG for neurological and oncological applications. Its novel use for imaging iron-52 transferrin for localising erythropoietic activity demonstrates its sensitivity and resolution advantages over a conventional dual-headed gamma camera. The ECAT ART provides a viable alternative to conventional full ring PET scanners without compromising the performance required for clinical PET imaging.