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Segmental challenge with allergen or endotoxin is a powerful tool to study mechanisms of airway inflammation and to test for efficacy of anti-inflammatory compounds. The assessment of airway inflammation by bronchoalveolar lavage (BAL) requires a bronchoscopy. Moreover, repetitive procedures to study inflammation over time are not possible. Noninvasive assessment of airway inflammation by magnetic resonance imaging (MRI) might add to the diagnostic armamentarium and might allow for sequential assessment of inflammation. 11 Patients with mild intermittent allergic asthma with positive responses to inhaled allergen (either grass mix or house dust mite) underwent segmental allergen challenges. After a baseline (B) BAL, four segments were instilled with either saline (S: right upper lobe), a low dose of allergen (LA: medial segment of the right middle lobe), or a high dose of allergen in two segments of contralateral lungs (HA: lateral segment of the right middle lobe and a lingular segment). MRI at 1.5T (Avanto, Siemens, Germany) was acquired 6 hours and 24 hours after segmental challenge using different sequences (TrueFISP, VIBE, T2HASTE, and T2-TIRM). Introduction

Bronchial wall thickness measurements in computed tomography (CT) has become a useful tool for assessment of the severity of diseaseand the response to treatment in a large number of pulmonary diseases. However, there are only few reports evaluating its dependence on different scan protocols. The effect of intravenous contrast medium has not been analyzed. The aim of this study was to evaluate the influence of intravenous contrast medium application, the contrast phase (arterial and venous) and different reconstruction kernels on bronchial wall measurements of a newly developed algorithm. The bronchial wall thickness was analyzed in 630 bronchial sections of 56 CT examinations with dedicated software (MEVIS Airway Examiner, Fraunhofer MEVIS Bremen, Germany). Application of i.v. contrast agent significantly increased bronchial wall thickness (paired t-test, p < 0.001). Comparing arterial and venous phase, bronchial wall thickness was significant higher in the arterial ph ase (paired t-test, p = 0.045). Bronchial wall thickness also increased (ANOVA with Bonferroni correction, p < 0.001) when using a softer reconstruction kernel. The absolute differences in bronchial wall thickness were independent of bronchial size and generation.

Despite the success of ultrasound elasticity imaging (USEI) in medical applications such as diagnosis and screening of breast lesions and prostate cancer, USEI has not been adopted in routine clinical procedures. This is partly caused by the difficulty in acquiring reliable images and interpreting them, the lack of consistency over time, and the dependency of image quality to the expertise of the user. We previously demonstrated the potential of exploiting an external tracker to partially alleviate these issues and enhance the quality of USEI. The tracking data enabled fast and automatic selection of pairs of RF frames used in strain calculation. Here, we expand this method by including new features. The proposed method employs image content to compensate for the limited accuracy of the tracking device. It also combines multiple strain images to improve the quality of the final image. For this purpose, It normalizes the images and determines which images can be combined relying on the tracking information. We have acquired RF frames synchronized with tracking data from livers of pig containing an ablated region and a breast phantom using two different tracking devices; an optical tracker and a less accurate electromagnetic tracker. We present the promising results of the proposed method and investigate the sensitivity of frame selection technique without using the image content to inaccuracies in tracking information.

Out-of-plane motion in freehand 3D ultrasound can be estimated using the correlation of corresponding patches, leading to sensorless freehand 3D ultrasound systems. The correlation between two images is related to their distance by calibrating the ultrasound probe: the probe is moved with an accurate stage (or with a robot in this work) and images of a phantom are collected, such that the position of each image is known. Since parts of the calibration curve with higher derivative gives lower displacement estimation error, previous work limits displacement estimation to parts with maximum derivative. In this paper, we first propose a novel method for exploiting the entire calibration curve by using a maximum likelihood estimator (MLE). We then propose for the first time using constrains inside the image to enhance the accuracy of out-of-plane motion estimation. We specifically use continuity constraint of a needle to reduce the variance of the estimated out-of-plane motion. Simulation and real tissue experimental results are presented.

To test the hypothesis that magnetic resonance (MR) imaging can be used to monitor both intraparenchymal injection of NaCl solution and subsequent radiofrequency ablation (RFA) within tissues pretreated with NaCl, report the low- and high-field-strength MR appearance of NaCl-enhanced RFAs, and compare MR findings with pathologic findings.Ten ex vivo calf liver specimens were injected with saturated NaCl (seven were mixed with methylene blue during MR fluoroscopic monitoring) and reexamined with fast imaging with steady-state progression (FISP), true FISP, reversed FISP (PSIF), and fast spin-echo T2-weighted MR sequences. The NaCl-to-liver contrast-to-noise ratio (CNR) was calculated for various sequences, and CNRs were compared with the Student t test. Distribution on MR images was compared with the results of pathologic analysis. Forty additional in vivo monopolar RFAs were performed in paraspinal muscles of seven minipigs after animal care committee approval (10 standard control ablations, 30 were preceded by direct injection of saturated NaCl at various volumes [3-9 mL] and rates [1 or 6mL/min]). Postablation low-field-strength (n = 20) and high-field-strength (n = 20) MR examinations consisted of T2-weighted imaging, short inversion time inversion-recovery (STIR) imaging, and contrast material-enhanced T1-weighted imaging. Ablation shape, conspicuity, volume, and signal intensity were compared between the two groups and with the results of pathologic analysis. The difference in volumes with and without NaCl injection was evaluated by using two-way analysis of variance.Mean CNR was highest on fast spin-echo T2-weighted images and was significantly higher for PSIF than for FISP (P.0001) or true FISP (P = .003). NaCl distribution on MR images corresponded with the results of pathologic analysis in ex vivo livers. Interactive in vivo monitoring of NaCl injection and electrode placement was feasible. NaCl-enhanced ablations had irregular shapes, a higher CNR, and significantly larger volumes (F = 22.0; df = 1, 90; P.00001). All ablations had intermediate or low signal intensity with high-signal-intensity rims on all images. Fluid signals overlaid NaCl-enhanced ablations on fast spin-echo T2-weighted and STIR images, particularly on high-field-strength MR images.MR imaging can be used to reliably monitor the distribution of injected NaCl solution in tissues. Interventional MR imaging techniques can be used to guide and monitor RFAs within NaCl pretreated tissues, with good correlation with pathologic results.

Background and objectives Stem cell therapies, although promising for treating ischemic arterial diseases, suffer from poor engraftment and the inability to noninvasively monitor and track transplanted cells in vivo. Stem cell microencapsulation in conjunction with an imaging contrast agent provides a means to prevent cell immunorejection and enable cell tracking with appropriate imaging modalities. The objective of this study was to design and evaluate a novel MRIand CT-visible, immunoprotectable alginate microcapsule containing an imaging contrast agent, perfluorooctylbromide (PFOB), for mesenchymal stem cell (MSC) delivery.

INTRODUCTION Coronary angiography remains the “gold standard” for the diagnosis of epicardial coronary artery disease. However, precise quantification of lesions severity is limited because of the complex three-dimensional geometry of epicardial plaques. Moreover, coronary physiology and physiopathological effects of lesions cannot be determined.1-3 Accurate identification of both normal and diseased vessel segments is complicated by diffuse disease as well as by angiographic artefacts of contrast streaming, image foreshortening, and calcification. Bifurcation or ostial lesion locations may be obscured and difficult to assess by overlapping branch segments. Measurements of coronary pressure and flow provide complementary information to the anatomic characterization of coronary disease obtained by both angiographic and intravascular ultrasound examinations. In particular, fractional flow reserve (FFR) has been demonstrated to be a useful tool to easily and reliably assess lesions significance and physiopathology.4 FFR in the catheterization laboratory can facilitate timely and more objective decision making about therapy, especially in complex and difficult settings. Table 15.1 summarizes current recommendations for the application of physiologic measurements with FFR, and shows how its use in more complex settings is still under investigation.5 In this chapter, we describe the utility and limitations of this technique in particular complex situations, such as ostial location, bifurcation, tandem lesions, ectasic vessel, and in-stent restenosis (Table 15.1).

Following the same format as previous volumes in this series, Direct Diagnosis in Radiology: Vascular Imaging , edited by Professor Karl-Juergen Wolf, presents the reader with a wide range of vascular pathologies involving the brain, spine, head and neck, chest, abdomen, kidneys, and extremities.

The purpose of the study was to prospectively evaluate intrahepatic vessel depiction on C-arm CT (CACT) and the influence of the additional combined tissue and three-dimensional vessel visualisation on the positioning of the TACE catheter in comparison to DSA alone. Thirty consecutive patients scheduled for their first transarterial chemoembolisation underwent biphasic CACT and DSA of the liver. After assessing the DSA images for procedure planning, the CACT images were reviewed. The number and origin of the tumour-feeding arteries and the ideal position of the catheter for TACE on both DSA and CACT were assessed and correlated. The number of vessels identified as tumour feeders in each patient was significantly higher using additional CACT than on DSA alone (CACT: 4.0 +/- 1.7; DSA: 3.3 +/- 1.4; P = 0.003, t-test). After considering CACT, in 50% of the patients the catheter position was changed for TACE. Segmental portal vein thrombosis was seen in three patients on CACT, but in only one on DSA. As CACT depicts soft tissue and small vessels with high spatial resolution, tumour vessel allocation is facilitated, and ideal catheter position for TACE can be more accurately identified. The high impact of CACT on the TACE procedure suggests the benefits of its routine use for all patients undergoing their first TACE.

Background: The characterization of brain arteriovenous malformation (AVM) angioarchitecture remains rewarding in planning and predicting therapy. The increased signal-to-noise ratio at higher field strength has been found advantageous in vascular brain pathologies. Purpose: To evaluate whether 3.0T time-of-flight (TOF) magnetic resonance angiography (MRA) is superior to 1.5T TOF-MRA for the characterization of cerebral AVMs. Material and Methods: Fifteen patients with AVM underwent TOF-MRA at 3.0T and 1.5T and catheter angiography (DSA), which was used as the gold standard. Blinded readers scored image quality on a four-point scale, nidus size, and number of feeding arteries and draining veins. Results: Image quality of TOF-MRA at 3.0T was superior to 1.5T but still inferior to DSA. Evaluation of nidus size was equally good at 3.0T and 1.5T for all AVMs. In small AVMs, however, there was a tendency of size overestimation at 3.0T. MRA at 3.0T had increased detection rates for feeding arteries (+21%) and superficial (+13%) and deep draining veins (+33%) over 1.5T MRA. Conclusion: 3.0T TOF-MRA offers superior characterization of AVM angioarchitecture compared with 1.5T TOF-MRA. The image quality of MRA at both 3.0 and 1.5T is still far from equal to DSA, which remains the gold standard for characterization of AVM.

A navigation system can increase the speed and accuracy of MR guided interventions that make use of scanners with high-field closed magnets. We report on first needle placement experiments performed with an Augmented Reality (AR) navigation system. AR visualization provides very intuitive guidance, resulting in a faster procedure. The accuracy of the needle placement depends on the registration accuracy of the system. In the present trials, the needle was placed as good as 1mm close to the target center, however in a small number of cases substantially larger errors occurred and were most likely caused by needle bending.

Interventional procedures using magnetic resonance imaging (MRI) guidance have increased in interest during the last few years. Central to the success and safety of MRI-guided procedures is the accurate visualization of the interventional instruments relative to the surrounding anatomy. A variety of methodologies for visualizing and automatically tracking instruments, including needles, radiofrequency and laser ablation devices, endoscopes, catheters, and guidewires have been developed and introduced to help the interventionalist to safely guide the device toward the target region. This article describes and compares characteristics of the four most commonly used localization and tracking systems used for MRI-guided interventional procedures: those based on the susceptibility artifact of the device, those that intentionally create field inhomogeneity along the device, those that rely on an optical tracking system, and active tracking systems using micro receive coils.

Introduction: Treating liver tumors by in situ ablation techniques such as laser induced thermotherapy (LITT) creates thermal lesions with complex lesion geometry. The aim of this study was to develop and evaluate a computer-simulated 3-D irradiation model for predicting the thermal volume in LITT. Material and Methods: Light and heat distribution in the tissue was calculated by using a Monte Carlo simulation. We first established a tissue database (human/animal/healthy/tumorous, n = 120 samples). A 3-D image of the coagulation volume was created and the simulation results were correlated to those in vivo in 15 domestic pigs. The animals were randomized into three groups: normal hepatic perfusion; interrupted perfusion by Pringle maneuver; i.a. embolization by starch microspheres. Results: Simulating the coagulation volume required 28.5 (23 – 27) min. Simulated or in vivo interrupted perfusion led to a 4.5-fold (DSM) or 10-fold (Pringle) increase in lesion volume. The deviation in the diameter between the simulation and in vivo data was a maximum of 3.1% ± 0.3 ( LITT mono ) , 2.6% ± 0.3 (LITTPringle ) and 15.6% ± ( LITTDSM ). Conclusion: The developed 3-D irradiation model showed very good prediction of the coagulation volume in LITT. It is now possible for the first time to make a statement about the expected lesion geometry and the application parameters required for reliable tumor destruction during in situ ablation procedures.

The objective of this study was to demonstrate in an animal model the feasibility of a passive tracking technique for catheter visualization of magnetic resonance (MR)-guided endovascular procedures. All experiments were performed in a 0.2 Tesla open MR system. Susceptibility-based catheters and guide wires were introduced into the aorta and were advanced selectively into the splenic and renal arteries under MR guidance. Based on a previously acquired contrast-enhanced magnetic resonance angiography (MRA) data set, the catheter positioning was performed by using a single-slice true fast imaging with steady state precession (FISP) sequence with a frame rate of 1.3 seconds. Contrast-enhanced MRA was performed in all animals. All catheters were advanced without complications into the aorta and were introduced into the proximal parts of the right renal and splenic arteries under MR guidance. Catheter manipulations were more difficult in the distal parts of these vessels due to the more complex anatomy. Passive catheter tracking is a valuable and technically robust alternative to active tracking methods, because it does not require additional hardware and, thus, can be implemented and used easily with any open MR imaging system. J. Magn. Reson. Imaging 1999;10:841–844. © 1999 Wiley-Liss, Inc.

Objectives To utilize a novel objective approach combining a software phantom and an image quality metric to systematically evaluate the influence of sinogram affirmed iterative reconstruction (SAFIRE) of multidetector computed tomography (MDCT) data on image noise characteristics and low-contrast detectability (LCD). Materials and Methods A low-contrast and a high-contrast phantom were examined on a 128-slice scanner at different dose levels. The datasets were reconstructed using filtered back projection (FBP) and SAFIRE and virtual low-contrast lesions (-20HU) were inserted. LCD was evaluated using the multiscale structural similarity index (MS-SIM*). Image noise texture and spatial resolution were objectively evaluated. Results The use of SAFIRE led to an improvement of LCD for all dose levels and lesions sizes. The relative improvement of LCD was inversely related to the dose level, declining from 208%(±37%), 259%(±30%) and 309%(±35%) at 25mAs to 106%(±6%), 119%(±9%) and 123%(±8%) at 200mAs for SAFIRE filter strengths of 1, 3 and 5 (p

20013 Background: The liver is the predominant site of metastases in the majority of patients with uveal melanoma. Response rates to systemic chemotherapy are low and median survival is very short ...