Recommendations for Imaging Patients With Cardiac Implantable Electronic Devices (CIEDs).

Historically, the presence of cardiac implantable electronic devices (CIEDs), including pacemakers and implantable cardioverter defibrillators (ICDs), was widely considered an absolute contraindication to magnetic resonance imaging (MRI). The recent development of CIEDs with MR Conditional labeling, as well as encouraging results from retrospective studies and a prospective trial on the safety of MRI performed in patients with CIEDs without MR Conditional labeling, have led to a reevaluation of this practice. The purpose of this report is to provide a concise summary of recent developments, including practical guidelines that an institution could adopt for radiologists who choose to image patients with CIEDs that do not have MR Conditional labeling. This report was written on behalf of and approved by the International Society for Magnetic Resonance in Medicine (ISMRM) Safety Committee. LEVEL OF EVIDENCE: 3. TECHNICAL EFFICACY STAGE: 1.

Max-IDEAL: a max-flow based approach for IDEAL water/fat separation.

PURPOSE: To propose a novel approach to water/fat separation using a unique smoothness constraint. THEORY AND METHODS: Chemical-shift based water/fat separation is an established noninvasive imaging tool for the visualization of body fat in various anatomies. Nevertheless, B0 magnetic field inhomogeneities can hamper the water/fat separation process. In this work, B0 variations are mapped using a convex-relaxed labeling model which produces a coarse estimate of the field map, while considering T2* decay during the labeling process. Fat and water components are subsequently resolved using T2*-IDEAL. An adaptive spatial filtering (ASF) was introduced to improve the robustness of the estimate. The method was tested on cardiac and abdominal datasets from healthy volunteers and nonalcoholic fatty liver disease (NAFLD) patients. RESULTS: Out of 168 cardiac and abdominal images, only 1 case has shown water/fat swaps that can hinder the clinical interpretation of the underlying anatomy. CONCLUSION: This work demonstrates a new water/fat separation approach that prevents the occurrence of water/fat swaps, by means of a unique smoothness constraint. Incorporating T2* effect in the labeling procedure and including the ASF processing enhance the robustness of the proposed approach and permit the procedure to handle abrupt B0 variations within the field of view.

Whole-heart chemical shift encoded water-fat MRI.

PURPOSE: To develop and evaluate a free-breathing chemical-shift-encoded (CSE) spoiled gradient-recalled echo (SPGR) technique for whole-heart water-fat imaging at 3 Tesla (T). METHODS: We developed a three-dimensional (3D) multi-echo SPGR pulse sequence with electrocardiographic gating and navigator echoes and evaluated its performance at 3T in healthy volunteers (N = 6) and patients (N = 20). CSE-SPGR, 3D SPGR, and 3D balanced-SSFP with chemical fat saturation were compared in six healthy subjects with images evaluated for overall image quality, level of residual artifacts, and quality of fat suppression. A similar scoring system was used for the patient datasets. RESULTS: Images of diagnostic quality were acquired in all but one subject. CSE-SPGR performed similarly to SPGR with fat saturation, although it provided a more uniform fat suppression over the whole field of view. Balanced-SSFP performed worse than SPGR-based methods. In patients, CSE-SPGR produced excellent fat suppression near metal. Overall image quality was either good (7/20) or excellent (12/20) in all but one patient. There were significant artifacts in 5/20 clinical cases. CONCLUSION: CSE-SPGR is a promising technique for whole-heart water-fat imaging during free-breathing. The robust fat suppression in the water-only image could improve assessment of complex morphology at 3T and in the presence of off-resonance, with additional information contained in the fat-only image.

Effectiveness of MR angiography for the primary diagnosis of acute pulmonary embolism: clinical outcomes at 3 months and 1 year.

PURPOSE: To determine the effectiveness of MR angiography for pulmonary embolism (MRA-PE) in symptomatic patients. MATERIALS AND METHODS: We retrospectively reviewed all patients whom were evaluated for possible pulmonary embolism (PE) using MRA-PE. A 3-month and 1-year from MRA-PE electronic medical record (EMR) review was performed. Evidence for venous thromboembolism (VTE) (or death from PE) within the year of follow-up was the outcome surrogate for this study. RESULTS: There were 190 MRA-PE exams performed with 97.4% (185/190) of diagnostic quality. There were 148 patients (120 F: 28 M) that had both a diagnostic MRA-PE exam and 1 complete year of EMR follow-up. There were 167 patients (137 F: 30 M) with 3 months or greater follow-up. We found 83% (139/167) and 81% (120/148) MRA-PE exams negative for PE at 3 months and 1 year, respectively. Positive exams for PE were seen in 14% (23/167). During the 1-year follow-up period, five patients (false negative) were diagnosed with DVT (5/148 = 3.4 %), and one of these patients also experienced a non-life-threatening PE. The negative predictive value (NPV) for MRA-PE was 97% (92-99; 95% CI) at 3 months and 96% (90-98; 95% CI) with 1 year of follow-up. CONCLUSION: The NPV of MRA-PE, when used for the primary diagnosis of pulmonary embolism in symptomatic patients, were found to be similar to the published values for CTA-PE. In addition, the technical success rate and safety of MRA-PE were excellent.

R*(2) mapping in the presence of macroscopic B0 field variations.

R2 mapping has important applications in MRI, including functional imaging, tracking of super-paramagnetic particles, and measurement of tissue iron levels. However, R2 measurements can be confounded by several effects, particularly the presence of fat and macroscopic B0 field variations. Fat introduces additional modulations in the signal. Macroscopic field variations introduce additional dephasing that results in accelerated signal decay. These effects produce systematic errors in the resulting R2 maps and make the estimated R2 values dependent on the acquisition parameters. In this study, we develop a complex-reconstruction, confounder-corrected R2 mapping technique, which addresses the presence of fat and macroscopic field variations for both 2D and 3D acquisitions. This technique extends previous chemical shift-encoded methods for R2, fat and water mapping by measuring and correcting for the effect of macroscopic field variations in the acquired signal. The proposed method is tested on several 2D and 3D phantom and in vivo liver, cardiac, and brain datasets.

Multimodality image fusion to guide peripheral artery chronic total arterial occlusion recanalization in a swine carotid artery occlusion model: unblinding the interventionalist.

OBJECTIVES: To demonstrate the feasibility of magnetic resonance imaging (MRI) to X-ray fluoroscopy (XRF) image fusion to guide peripheral artery chronic total occlusion (CTO) recanalization. BACKGROUND: Endovascular peripheral artery CTO revascularization is minimally invasive, but challenging, because the occlusion is poorly visualized under XRF. Devices may steer out of the artery, which can lead to severe perforation. Merging preacquired MRI of the CTO to the live XRF display may permit upfront use of aggressive devices and improve procedural outcomes. METHODS: Swine carotid artery CTOs were created using a balloon injury model. Up to 8 weeks later, MRI of the carotid arteries was acquired and segmented to create three-dimensional surface models, which were then registered onto live XRF. CTO recanalization was performed using incrementally aggressive CTO devices (group A) or an upfront aggressive directed laser approach (group B). Procedural success was defined as luminal or subintimal device position without severe perforation. RESULTS: In this swine model, MRI to XRF fusion guidance resulted in a procedural success of 57% in group A and 100% in group B, which compared favorably to 33% using XRF alone. Fluoroscopy time was significantly less for group B (8.5 ± 2.6 min) compared to group A (48.7 ± 23.9 min), P < 0.01. Contrast dose used was similar between groups A and B. CONCLUSIONS: MRI to XRF fusion-guided peripheral artery CTO recanalization is feasible. Multimodality image fusion may permit upfront use of aggressive CTO devices with improved procedural outcomes compared to XRF-guided procedures.

Optimized high-resolution contrast-enhanced hepatobiliary imaging at 3 tesla: a cross-over comparison of gadobenate dimeglumine and gadoxetic acid.

PURPOSE: To evaluate the signal to noise ratio (SNR) and contrast to noise ratio (CNR) performance of 0.05 mmol/kg gadoxetic acid and 0.1 mmol/kg gadobenate dimeglumine for dynamic and hepatobiliary phase imaging. In addition, flip angles (FA) that maximize relative contrast-to-noise performance for hepatobiliary phase imaging were determined. MATERIALS AND METHODS: A cross-over study in 10 volunteers was performed using each agent. Imaging was performed at 3 Tesla (T) with a 32-channel phased-array coil using breathheld 3D spoiled gradient echo sequences for SNR and CNR analysis, and for FA optimization of hepatobiliary phase imaging. RESULTS: Gadobenate dimeglumine (0.1 mmol/kg) had superior SNR performance during the dynamic phase, statistically significant for portal vein and hepatic vein in the portal venous and venous phase (for all, P < 0.05) despite twice the approved dose of gadoxetic acid (0.05 mmol/kg), while gadoxetic acid had superior SNR performance during the hepatobiliary phase. Optimal FAs for hepatobiliary phase imaging using gadoxetic acid and gadobenate dimeglumine were 25-30° and 20-30° for relative contrast liver versus muscle (surrogate for nonhepatocellular tissues), and 45° and 20° (relative contrast liver versus biliary structures), respectively. CONCLUSION: Gadobenate dimeglumine may be preferable for applications that require dynamic phase imaging only, while gadoxetic acid may be preferable when the hepatobiliary phase is clinically important. Hepatobiliary phase imaging with both agents benefits from flip angle optimization.

T(1) independent, T(2) (*) corrected chemical shift based fat-water separation with multi-peak fat spectral modeling is an accurate and precise measure of hepatic steatosis.

PURPOSE: To determine the precision and accuracy of hepatic fat-fraction measured with a chemical shift-based MRI fat-water separation method, using single-voxel MR spectroscopy (MRS) as a reference standard. MATERIALS AND METHODS: In 42 patients, two repeated measurements were made using a T(1) -independent, T 2*-corrected chemical shift-based fat-water separation method with multi-peak spectral modeling of fat, and T(2) -corrected single voxel MR spectroscopy. Precision was assessed through calculation of Bland-Altman plots and concordance correlation intervals. Accuracy was assessed through linear regression between MRI and MRS. Sensitivity and specificity of MRI fat-fractions for diagnosis of steatosis using MRS as a reference standard were also calculated. RESULTS: Statistical analysis demonstrated excellent precision of MRI and MRS fat-fractions, indicated by 95% confidence intervals (units of absolute percent) of [-2.66%,2.64%] for single MRI ROI measurements, [-0.81%,0.80%] for averaged MRI ROI, and [-2.70%,2.87%] for single-voxel MRS. Linear regression between MRI and MRS indicated that the MRI method is highly accurate. Sensitivity and specificity for detection of steatosis using averaged MRI ROI were 100% and 94%, respectively. The relationship between hepatic fat-fraction and body mass index was examined. CONCLUSION: Fat-fraction measured with T(1) -independent T 2*-corrected MRI and multi-peak spectral modeling of fat is a highly precise and accurate method of quantifying hepatic steatosis.

Targeted transendocardial therapeutic delivery guided by MRI-x-ray image fusion.

OBJECTIVES: To validate a multi-modality image fusion approach to guide catheter-based, targeted transendocardial therapeutic delivery in a swine myocardial infarction (MI) model. BACKGROUND: Biologic agents such as stem cells may curb post MI adverse ventricular remodeling if delivered by a transendocardial catheter directly into the infarct border. 3D visualization of the infarct and other cardiac surfaces is required to perform this task. We propose registering and overlaying magnetic resonance imaging (MRI) roadmaps onto live x-ray fluoroscopy (XRF) to guide targeted transendocardial delivery. METHODS: Custom software was used to register and overlay MRI models of the endocardium and infarct on live XRF by aligning common endocardial border features. In a swine MI model, transendocardial injections of co-localizing imaging labels were performed, targeting a 20 mm perimeter around the infarct. Directed targeting error (DTE) was defined as the difference between the predicted injection site-to-infarct distance calculated by the image fusion system, to the actual distance determined by postprocedure in vivo MRI. The mobile image fusion system was designed to be vendor-independent for imaging systems and transendocardial catheters. RESULTS: Transendocardial injections were performed in all animals without complications. Mean DTE was 0.9 ± 5.0 mm (n = 8 swine). Time to register the images and establish a high quality roadmap was less than 12 min in all animals. Custom imaging tools to display injection sites and distribution were useful adjuncts during targeted injection procedures. CONCLUSIONS: Multi-modality image fusion is a feasible and accurate platform technology to guide transendocardial injections precisely to the discrete infarct border.

Magnetic resonance imaging-monitored plasmid DNA delivery in primate limb muscle.

The purpose of this work is to investigate the use of magnetic resonance imaging (MRI) to monitor the effects of high-pressure naked plasmid DNA (pDNA) intravascular injections in primate limbs, studying both the distribution of the injected solution in the muscle space, as well as the effects on the vascular system. The distal portion of the four limbs of each of six rhesus monkeys were hydrodynamically injected with naked pDNA, which expressed the luciferase reporter gene. Three-dimensional (3D) T1-weighted gradient echo and 2D multislice T2-weighted fast spin echo (FSE) series were acquired before and immediately after the injection to confirm the volume of solution injected into the limb, and to study the distribution of the injected solution in the individual muscle groups. Time-resolved contrast-enhanced 3D magnetic resonance angiography (MRA) was performed several days before, immediately after, and in a follow-up examination after the pDNA injection to study the effects of the procedure on the primate peripheral vascular system. T1-weighted gradient echo imaging confirmed the delivery of the majority of the solution after successful pDNA injections. T2-weighted FSE imaging demonstrated the distribution of the saline solution in individual muscles in the target limbs, with enhancement showing a weak but significant correlation with the level of gene expression. Time-resolved contrast-enhanced MRA demonstrated effects of the injection procedure on the arterial and venous vascular systems, and the intramuscular compartments; and these effects largely returned to normal on short-term follow-up.

Contrast enhanced pulmonary magnetic resonance angiography for pulmonary embolism: Building a successful program.

The performance of contrast enhanced pulmonary magnetic resonance angiography (MRA) for the diagnosis of pulmonary embolism (PE) is an effective non-ionizing alternative to contrast enhanced computed tomography and nuclear medicine ventilation/perfusion scanning. However, the technical success of these exams is very dependent on careful attention to the details of the MRA acquisition protocol and requires reader familiarity with MRI and its artifacts. Most practicing radiologists are very comfortable with the performance and interpretation of computed tomographic angiography (CTA) performed to detect pulmonary embolism but not all are as comfortable with the use of MRA in this setting. The purpose of this review is to provide the general radiologist with the tools necessary to build a successful pulmonary embolism MRA program. This review will cover in detail image acquisition, image interpretation, and some key elements of outreach that help to frame the role of MRA to consulting clinicians and hospital administrators. It is our aim that this resource will help build successful clinical pulmonary embolism MRA programs that are well received by patients and physicians, reduce the burden of medical imaging radiation, and maintain good patient outcomes.

Incidence of actionable findings on contrast enhanced magnetic resonance angiography ordered for pulmonary embolism evaluation.

PURPOSE: To determine the incidence of actionable findings on contrast-enhanced magnetic resonance angiography (MRA) scans performed for the primary diagnosis of pulmonary embolism (PE). MATERIALS AND METHODS: This was a HIPAA-compliant and IRB-approved single center, retrospective study of consecutive series of patients evaluated with contrast-enhanced MRA for PE. The final radiology report of each MRA was reviewed. All technically adequate negative exams were included in the analysis. The findings were divided into three types: those requiring further action (actionable-Type 1) those not requiring follow-up (non-actionable-Type 2) and normal exams. We compared our results with the literature regarding the use of computed tomographic angiography (CTA) in this scenario using Fisher's exact test. RESULTS: 580 MRA scans for PE were performed. There were 561/580 (97%) technically adequate exams. Of these, 514/580 (89%) were negative and 47/580 (8%) were positive for PE. In the PE negative group of 514 exams, Type 1 findings were identified in 85/514 (17%), 188/514 (36%) cases were Type 2 and 241/514 (47.0%) were Type 3. There was no significant difference between the incidence of Type 1 and the combination of Type 2 and Type 3 findings on MRA and the reported incidence of actionable findings derived from CTA negative exams for PE (p<0.5). CONCLUSION: MRA as a first-line test for PE can identify actionable findings in those patients without PE, with an incidence similar to that reported in the literature for CTA.

In vivo MR thermometry of frozen tissue using R2* and signal intensity.

Cryoablation is one of several minimally invasive treatments that may be suitable for a targeted treatment of prostate cancer. Because efficacy is improved when a sufficiently cold end temperature is reached, the purpose of this work was to demonstrate an image-based thermometry method that could provide temperature maps throughout the frozen tissue. In five in vivo canine prostate cryoablation experiments performed under magnetic resonance imaging guidance, two MR parameters were measured and correlated to temperature: R2* and changes in signal intensity. R2* is elevated approximately linearly as tissue temperature decreases below the freezing point, while the signal intensity decreases exponentially. In vivo temperature maps with isotherms at -5 degrees C, -15 degrees C, and -30 degrees C are demonstrated.

Effect of hepatocyte-specific gadolinium-based contrast agents on hepatic fat-fraction and R2(⁎).

The purpose of this work was to investigate the effect of a hepatocyte-specific gadolinium based contrast agent (GBCA) on quantitative hepatic fat-fraction (FF) and R2* measurements. Fifty patients were imaged at 1.5T, using chemical-shift encoded water-fat MRI with low (5°) and high (15°) flip angles (FA), both before and after administration of a hepatocyte-specific GBCA (gadoxetic acid). Low and high FA, pre- and post-contrast FF and R2* values were measured for each subject. Available serum laboratory studies related to liver disease were also recorded. Linear regression and Bland-Altman analysis were performed to compare measurements. Hepatic FF was unaffected by GBCA at low FA (slope=1.02±0.02, p=0.32). FF was overestimated at high FA pre-contrast (slope=1.33±0.03, p<10(-10)), but underestimated post-contrast (slope=0.81±0.02, p<10(-10)). Hepatic R2* was unaffected by FA (mean difference±95% CI pre-contrast:2.2±4.9s(-1), post-contrast:2.8±3.6s(-1)), but increased post-contrast in patients with total bilirubin <2.5mg/dL (ΔR2*=13.4±12.7s(-1)). Regression analysis of serum values demonstrated a correlation of post-contrast change in R2* with total bilirubin (p<0.01) and model for end-stage liver disease (MELD) score (p≈0.01). In conclusion, GBCA has no effect on hepatic FF at low FA due to a lack of T1-weighting, potentially allowing flexibility for FF imaging with hepatobiliary imaging protocols. Hepatic R2* increased significantly after GBCA administration, particularly in the biliary tree. Therefore, R2* maps should be obtained prior to contrast administration.

Single breath hold 3D cardiac cine MRI using kat-ARC: preliminary results at 1.5T.

Validation of a new single breath-hold, three-dimensional, cine balanced steady-state free precession (3D cine bSSFP) cardiac magnetic resonance (CMR) sequence for left ventricular function. CMR examinations were performed on fifteen patients and three healthy volunteers on a clinical 1.5T scanner using a two-dimensional (2D) cine balanced SSFP CMR sequence (2D cine bSSFP) followed by an investigational 3D cine bSSFP pulse sequence acquired within a single breath hold. Left ventricular end diastolic volume (LVEDV), end systolic volume (LVESV), ejection fraction (LVEF), and myocardial mass were independently segmented on a workstation by two experienced radiologists. Blood pool to myocardial contrast was evaluated in consensus using a Likert scale. Bland-Altman analysis was used to compare these quantitative and nominal measurements for the two sequences. The average acquisition time was significantly shorter for the 3D cine bSSFP than for 2D cine bSSFP (0.36 ± 0.03 vs. 8.5 ± 2.3 min) p = 0.0002. Bland-Altman analyses [bias and (limits of agreement)] of the data derived from these two methods revealed that the LVEF 0.9% (-4.7, 6.4), LVEDV 4.9 ml (-23.0, 32.8), LVESV -0.2 ml (-22.4, 21.9), and myocardial mass -0.4 g (-23.8, 23.0) were not significantly different. There was excellent intraclass correlation for intra-observer variability (0.981, 0.989, 0.997, 0.985) and inter-observer variability (0.903, 0.954, 0.970, 0.842) for LVEF, LVEDV, LVESV, and myocardial mass respectively. 3D cine bSSFP allows for accurate single breath-hold volumetric cine CMR which enables substantial improvements in scanner time efficiency without sacrificing diagnostic accuracy.

Intravenous Followed by X-ray Fused with MRI-Guided Transendocardial Mesenchymal Stem Cell Injection Improves Contractility Reserve in a Swine Model of Myocardial Infarction.

The aim of this study is to determine the effects of early intravenous (IV) infusion later followed by transendocardial (TE) injection of allogeneic mesenchymal stem cells (MSCs) following myocardial infarction (MI). Twenty-four swine underwent balloon occlusion reperfusion MI and were randomized into 4 groups: IV MSC (or placebo) infusion (post-MI day 2) and TE MSC (or placebo) injection targeting the infarct border with 2D X-ray fluoroscopy fused to 3D magnetic resonance (XFM) co-registration (post-MI day 14). Continuous ECG recording, MRI, and invasive pressure-volume analyses were performed. IV MSC plus TE MSC treated group was superior to other groups for contractility reserve (p = 0.02) and freedom from VT (p = 0.03) but had more lymphocytic foci localized to the peri-infarct region (p = 0.002). No differences were observed in post-MI remodeling parameters. IV followed by XFM targeted TE MSC therapy improves contractility reserve and suppresses VT but does not affect post-MI remodeling and may cause an immune response.

Wide-bore 1.5 T MRI-guided deep brain stimulation surgery: initial experience and technique comparison.

OBJECT: We report results of the initial experience with magnetic resonance image (MRI)-guided implantation of subthalamic nucleus (STN) deep brain stimulating (DBS) electrodes at the University of Wisconsin after having employed frame-based stereotaxy with previously available MR imaging techniques and microelectrode recording for STN DBS surgeries. METHODS: Ten patients underwent MRI-guided DBS implantation of 20 electrodes between April 2011 and March 2013. The procedure was performed in a purpose-built intraoperative MRI suite configured specifically to allow MRI-guided DBS, using a wide-bore (70 cm) MRI system. Trajectory guidance was accomplished with commercially available system consisting of an MR-visible skull-mounted aiming device and a software guidance system processing intraoperatively acquired iterative MRI scans. RESULTS: A total of 10 patients (5 male, 5 female)-representative of the Parkinson Disease (PD) population-were operated on with standard technique and underwent 20 electrode placements under MRI-guided bilateral STN-targeted DBS placement. All patients completed the procedure with electrodes successfully placed in the STN. Procedure time improved with experience. CONCLUSION: Our initial experience confirms the safety of MRI-guided DBS, setting the stage for future investigations combining physiology and MRI guidance. Further follow-up is required to compare the efficacy of the MRI-guided surgery cohort to that of traditional frame-based stereotaxy.

Influence of field strength on intracranial vessel conspicuity in canine magnetic resonance angiography.

Eight neurologically normal beagles were imaged using three-dimensional (3D) time-of-flight magnetic resonance angiography (MRA) in a 3T magnetic resonance scanner. Four of the eight dogs were also imaged using a 1T unit for comparison. Ten intracranial arteries were consistently identified at 3T: external and internal carotid, basilar, vertebral, rostral cerebral, middle cerebral, caudal cerebral, rostral communicating, caudal communicating, and ventral spinal arteries. Only four were reliably identified at 1T with diagnostic spatial and contrast resolution. At 3 T, vessels as small as 1 mm were reliably detected. Vessel conspicuity was superior using the 3T system. An anatomic atlas of the canine circulus arteriosus cerebri using a 3T scan was constructed. The effect of MRA parameters on vascular spatial resolution a nd conspicuity are reviewed.

In vivo porcine liver radiofrequency ablation with simultaneous MR temperature imaging.

PURPOSE: To demonstrate in vivo MR-guided temperature mapping during radiofrequency (RF) ablation of the liver with a commercially available RF generator modified to allow simultaneous RF treatment and MRI. MATERIALS AND METHODS: A commercial RF generator was modified using passive filtering to allow the continuous application of the treatment current during MRI studies. A total of six ablations were performed with the device in vivo in three porcine livers, and imaging was concurrently performed using one of two different temperature mapping strategies. RESULTS: MR images acquired during RF ablation demonstrated no noticeable interference from the RF ablation device, which was operated at clinically relevant power levels. Temperature maps showed areas of heating that were consistent with the dimensions of the RF ablation probe, with some asymmetry (likely depending on the orientation of the probe and heat propagation effects), and some differences in heating-spot area stability depending on the specific temperature mapping strategy used. Lesions were visualized on post-ablation imaging and sectioning. CONCLUSION: The feasibility of performing RF ablation with a modified commercial RF generator simultaneously with MRI was demonstrated. Interference-free MR temperature maps were produced with both variable respiratory motion and mechanical ventilation, and showed the extent of heating as the ablation progressed.

Cine flow measurements using phase contrast with undersampled projections: in vitro validation and preliminary results in vivo.

PURPOSE: To assess the accuracy of flow measurements in vitro and in vivo during scan times shorter than a breath-hold using a 2D cine phase contrast (PC) undersampled radial acquisition method, which may be useful for measuring flow, especially in vessels subject to motion during respiration. MATERIALS AND METHODS: For in vitro assessment, a flow phantom was imaged at various flow rates and undersampling factors. For in vivo assessment, five normal subjects were imaged and the flow rate in the aorta was compared with the sum of the flow rates in the iliac arteries. RESULTS: For results in vitro, the accuracy of flow measurements was maintained with scan times as low as 13-17 seconds. For results in vivo, scans acquired in less than 25 seconds provided flow measurements in the aorta that corresponded well to the sum of flow measurements in the iliac arteries. CONCLUSION: The undersampled radial acquisition cine PC technique provided accurate flow measurements in a flow phantom and in healthy human volunteers in scan times shorter than a typical breath-hold.