Direct Comparison of Bayesian and Fermi Deconvolution Approaches for Myocardial Blood Flow Quantification: In silico and Clinical Validations.

Cardiac magnetic resonance myocardial perfusion imaging can detect coronary artery disease and is an alternative to single-photon emission computed tomography or positron emission tomography. However, the complex, non-linear MR signal and the lack of robust quantification of myocardial blood flow have hindered its widespread clinical application thus far. Recently, a new Bayesian approach was developed for brain imaging and evaluation of perfusion indexes (Kudo et al., 2014). In addition to providing accurate perfusion measurements, this probabilistic approach appears more robust than previous approaches, particularly due to its insensitivity to bolus arrival delays. We assessed the performance of this approach against a well-known and commonly deployed model-independent method based on the Fermi function for cardiac magnetic resonance myocardial perfusion imaging. The methods were first evaluated for accuracy and precision using a digital phantom to test them against the ground truth; next, they were applied in a group of coronary artery disease patients. The Bayesian method can be considered an appropriate model-independent method with which to estimate myocardial blood flow and delays. The digital phantom comprised a set of synthetic time-concentration curve combinations generated with a 2-compartment exchange model and a realistic combination of perfusion indexes, arterial input dynamics, noise and delays collected from the clinical dataset. The myocardial blood flow values estimated with the two methods showed an excellent correlation coefficient (r 2 > 0.9) under all noise and delay conditions. The Bayesian approach showed excellent robustness to bolus arrival delays, with a similar performance to Fermi modeling when delays were considered. Delays were better estimated with the Bayesian approach than with Fermi modeling. An in vivo analysis of coronary artery disease patients revealed that the Bayesian approach had an excellent ability to distinguish between abnormal and normal myocardium. The Bayesian approach was able to discriminate not only flows but also delays with increased sensitivity by offering a clearly enlarged range of distribution for the physiologic parameters.

Aortic annular dimensions by non-contrast MRI using k-t accelerated 3D cine b-SSFP in pre-procedural assessment for transcatheter aortic valve implantation: a technical feasibility study.

To evaluate k-t accelerated 3D cine b-SSFP (balanced steady state free precession) as magnetic resonance imaging (MRI) technique for aortic annular area measurement in transcatheter aortic valve replacement (TAVR) planning compared to computed tomography angiography (CTA) and other non-contrast MRI sequences with reduced imaging time and without contrast administration. 6 volunteers and 7 TAVR candidates were prospectively enrolled. The volunteers underwent an MRI while TAVR candidates underwent an MRI and CTA. The following non-contrast MRI sequences were obtained at the level of the aortic root: 2D cine b-SSFP [GRAPPA (GeneRalized Autocalibrating Partially Parallel Acquisitions), R = 2], 3D cine b-SSFP [GRAPPA R = 2], navigator triggered 3D b-SSFP MRA [GRAPPA, R = 2] and k-t accelerated 3D cine b-SSFP [PEAK GRAPPA, R = 5]. Qualitative analysis and aortic annular area measurements in systole and diastole were obtained. k-t accelerated 3D cine b-SSFP provided image quality that is acceptable for confident diagnosis with very good interrater agreement. There was no statistically significant difference in aortic annular measurements between k-t accelerated 3D cine b-SSFP and CTA or other MRI sequences (p > 0.05). Bland-Altman analysis showed no systemic difference of annular area measurements between k-t accelerated 3D cine b-SSFP and each of the other techniques. There was excellent inter-rater agreement on aortic annular area measurements during systolic (ICC = 0.976, p < 0.001) and diastolic (ICC = 0.971, p < 0.001) phases using k-t accelerated 3D cine b-SSFP. K-t accelerated 3D cine b-SSFP is a promising alternative for the assessment of annular sizing in pre-TAVR evaluation while offering a reasonable combination of imaging parameters during one breath-hold.

An International Standardized Magnetic Resonance Imaging Protocol for Diagnosis and Follow-up of Patients with Multiple Sclerosis: Advocacy, Dissemination, and Implementation Strategies.

Standardized magnetic resonance imaging (MRI) protocols are important for the diagnosis and monitoring of patients with multiple sclerosis (MS). The Consortium of Multiple Sclerosis Centers (CMSC) convened an international panel of MRI experts to review and update the current guidelines. The objective was to update the standardized MRI protocol and clinical guidelines for diagnosis and follow-up of MS and develop strategies for advocacy, dissemination, and implementation. Conference attendees included neurologists, radiologists, technologists, and imaging scientists with expertise in MS. Representatives from the CMSC, Magnetic Resonance Imaging in MS (MAGNIMS), North American Imaging in Multiple Sclerosis Cooperative, US Department of Veteran Affairs, National Multiple Sclerosis Society, Multiple Sclerosis Association of America, MRI manufacturers, and commercial image analysis companies were present. Before the meeting, CMSC members were surveyed about standardized MRI protocols, gadolinium use, need for diffusion-weighted imaging, and the central vein sign. The panel worked to make the CMSC and MAGNIMS MRI protocols similar so that the updated guidelines could ultimately be accepted by international consensus. Advocacy efforts will promote the importance of standardized MS MRI protocols. Dissemination will include publications, meeting abstracts, educational programming, webinars, "meet the expert" teleconferences, and examination cards. Implementation will require comprehensive and coordinated efforts to make the protocol easy to access and use. The ultimate vision, and goal, is for the guidelines to be universally useful, usable, and used as the standard of care for patients with MS.

Retrospective Correction of ADC for Gradient Nonlinearity Errors in Multicenter Breast DWI Trials: ACRIN6698 Multiplatform Feasibility Study.

The presented analysis of multisite, multiplatform clinical oncology trial data sought to enhance quantitative utility of the apparent diffusion coefficient (ADC) metric, derived from diffusion-weighted magnetic resonance imaging, by reducing technical interplatform variability owing to systematic gradient nonlinearity (GNL). This study tested the feasibility and effectiveness of a retrospective GNL correction (GNC) implementation for quantitative quality control phantom data, as well as in a representative subset of 60 subjects from the ACRIN 6698 breast cancer therapy response trial who were scanned on 6 different gradient systems. The GNL ADC correction based on a previously developed formalism was applied to trace-DWI using system-specific gradient-channel fields derived from vendor-provided spherical harmonic tables. For quantitative DWI phantom images acquired in typical breast imaging positions, the GNC improved interplatform accuracy from a median of 6% down to 0.5% and reproducibility of 11% down to 2.5%. Across studied trial subjects, GNC increased low ADC (<1 µm2/ms) tumor volume by 16% and histogram percentiles by 5%-8%, uniformly shifting percentile-dependent ADC thresholds by ∼0.06 µm2/ms. This feasibility study lays the grounds for retrospective GNC implementation in multiplatform clinical imaging trials to improve accuracy and reproducibility of ADC metrics used for breast cancer treatment response prediction.

Cardiovascular magnetic resonance imaging of aorto-iliac and ilio-femoral vascular calcifications using proton density-weighted in-phase stack of stars.

BACKGROUND: Comparing cardiovascular magnetic resonance (CMR) angiography with computed tomography angiography (CTA), a major deficiency has been its inability to reliably image peripheral vascular calcifications that may impact the choice of interventional strategy and influence patient prognosis. Recently, MRI using a proton density-weighted, in-phase stack of stars (PDIP-SOS) technique has proved capable of detecting these calcifications. The goal of the present study was two-fold: (1) to determine whether magnetic field strength impacts the apparent size and conspicuity of ilio-femoral arterial calcifications; and (2) to determine whether the technique can be accurately applied to image aorto-iliac arterial calcifications. MAIN BODY: Two patient cohorts were studied. For the first cohort, ilio-femoral arterial calcifications were imaged at 1.5 Tesla in 20 patients and at 3 Tesla in 12 patients. For the second cohort, aorto-iliac arterial calcifications were imaged in 10 patients at 3 Tesla and one patient at 1.5 Tesla. Qualitative image analysis as well as quantitative analysis using a semi-automated technique were performed using CTA as the reference standard. Qualitatively, most PDIP-SOS CMR images showed good-to-excellent confidence to detect vascular calcifications, with good-to-excellent inter-reader agreement (κ = 0.67 for ilio-femoral region, P < 0.001; κ = 0.80 for aorto-iliac region, P < 0.01). There was an overall excellent correlation (r = 0.98, P < 0.001) and agreement (intraclass correlation coefficient = 0.97, P < 0.001) between PDIP-SOS CMR and CTA measures of calcification volume in both regions, with no overt difference in performance at 1.5 Tesla vs. 3 Tesla for ilio-femoral calcifications. CMR lesion volumes were slightly lower than those measured for CTA. CONCLUSION: Using PDIP-SOS CMR, aorto-iliac and ilio-femoral calcifications could be simultaneously evaluated at 3 Tesla in less than six minutes with excellent correlation and agreement to CTA. Our results suggest that PDIP-SOS CMR provides a reliable alternative to CT for pre-interventional evaluation of peripheral vascular calcium burden.

Single-Shot Coronary Quiescent-Interval Slice-Selective Magnetic Resonance Angiography Using Compressed Sensing: A Feasibility Study in Patients With Congenital Heart Disease.

OBJECTIVE: The aim of this study was to determine whether it is feasible to visualize the coronary origins in patients with congenital heart disease (CHD) using single-shot coronary quiescent-interval slice-selective (QISS) magnetic resonance angiography (MRA) with compressed sensing (CS). METHODS: This retrospective study leveraged a parent study, which aimed to compare breath-hold, 2.1-fold accelerated, 2-shot coronary QISS MRA and clinical standard contrast-enhanced (CE) MRA in 14 patients with CHD (mean age, 17.0 ± 8.6 years, 6 females and 8 males). We evaluated the feasibility of single-shot coronary QISS MRA by retrospectively undersampling the 2-shot data set by an additional factor of 2, performing CS reconstruction, and comparing the retrospectively derived single-shot QISS MRA to 2-shot coronary QISS MRA and clinical standard CE MRA. For quantitative analysis, structural similarity index and normalized root mean square error were calculated. For qualitative analysis, 2 experienced readers scored the conspicuity of coronary origins on a 5-point Likert scale (1 = nondiagnostic, 2 = poor, 3 = clinically acceptable, 4 = good, 5 = excellent). RESULTS: Compared with 2-shot QISS, single-shot QISS produced normalized root mean square error of 5.8% ± 0.8% and structural similarity index of 95.4% ± 1.6%, suggesting high data fidelity by CS reconstruction. Compared with the mean conspicuity scores for clinical CE MRA (4.2 ± 0.5 and 4.1 ± 0.6 for right and left coronary origins, respectively), the mean conspicuity scores were not significantly different (P > 0.3) for 2-shot QISS (4.4 ± 0.9 and 4.2 ± 1.1, respectively) and single-shot QISS with CS (4.3 ± 1.1 and 3.8 ± 1.3, respectively) and deemed clinically acceptable to good (scores ≥3.0). CONCLUSIONS: This study shows that it is feasible to visualize the coronary origins in patients with CHD with clinically acceptable to good image quality using single-shot coronary QISS MRA with CS.

Technical Feasibility of a Combined Noncontrast Magnetic Resonance Protocol for Preoperative Transcatheter Aortic Valve Replacement Evaluation.

PURPOSE: The aim of this study was to prospectively evaluate the technical feasibility of a noncontrast magnetic resonance angiography (MRA) protocol using investigational prototype self-navigated 3D (SN3D) radial whole-heart and quiescent-interval single-shot (QISS) pulse sequences regarding their potential in planning transcatheter aortic valve replacement (TAVR). MATERIALS AND METHODS: Five patients (76±7 y) with severe aortic valve stenosis and prior computed tomographic angiography (CTA) for TAVR planning and 10 healthy volunteers (28±6 y) underwent noncontrast MRA on a 1.5 T system. A SN3D whole-heart acquisition was used to assess the aortic root anatomy. Evaluation of the aortoiliac access route was performed with both SN3D and QISS. Measurements were compared among SN3D, QISS, and CTA using a paired t test or 1-way analysis of variance. Image quality ratings and contrast-to-noise ratios (CNR) were analyzed using Mann-Whitney U tests. Interobserver agreement was evaluated using Cohen's κ. RESULTS: The combined SN3D and QISS protocol provided a 10.1±1.6-minute acquisition time. TAVR-relevant evaluation was technically feasible in healthy volunteers. All measurements showed good agreement with CTA in patients (all P>0.098). SN3D and QISS produced similar image quality both in volunteers and in patients (all P>0.122). There was no difference in qualitative ratings between MRA and CTA (all P>0.119). Interobserver agreement was good for MRA (κ=0.71 to 0.76) and excellent for CTA (κ=0.82 to 0.84). Thoracic SN3D provided a similar CNR compared with CTA (P=0.117). CTA yielded higher CNR in the abdominopelvic region compared with QISS (P=0.006). CONCLUSIONS: A noncontrast MRA protocol combining SN3D and QISS acquisitions for the assessment of cardiac and vascular access route anatomy has technical feasibility for TAVR planning.

Identification of myocardial diffuse fibrosis by 11 heartbeat MOLLI T 1 mapping: averaging to improve precision and correlation with collagen volume fraction.

OBJECTIVES: Our objectives involved identifying whether repeated averaging in basal and mid left ventricular myocardial levels improves precision and correlation with collagen volume fraction for 11 heartbeat MOLLI T 1 mapping versus assessment at a single ventricular level. MATERIALS AND METHODS: For assessment of T 1 mapping precision, a cohort of 15 healthy volunteers underwent two CMR scans on separate days using an 11 heartbeat MOLLI with a 5(3)3 beat scheme to measure native T 1 and a 4(1)3(1)2 beat post-contrast scheme to measure post-contrast T 1, allowing calculation of partition coefficient and ECV. To assess correlation of T 1 mapping with collagen volume fraction, a separate cohort of ten aortic stenosis patients scheduled to undergo surgery underwent one CMR scan with this 11 heartbeat MOLLI scheme, followed by intraoperative tru-cut myocardial biopsy. Six models of myocardial diffuse fibrosis assessment were established with incremental inclusion of imaging by averaging of the basal and mid-myocardial left ventricular levels, and each model was assessed for precision and correlation with collagen volume fraction. RESULTS: A model using 11 heart beat MOLLI imaging of two basal and two mid ventricular level averaged T 1 maps provided improved precision (Intraclass correlation 0.93 vs 0.84) and correlation with histology (R 2 = 0.83 vs 0.36) for diffuse fibrosis compared to a single mid-ventricular level alone. ECV was more precise and correlated better than native T 1 mapping. CONCLUSION: T 1 mapping sequences with repeated averaging could be considered for applications of 11 heartbeat MOLLI, especially when small changes in native T 1/ECV might affect clinical management.

Noncontrast Hybrid Arterial Spin-Labeled Imaging of the Intracranial Arteries.

OBJECTIVE: The purpose of this study is to evaluate feasibility, image quality (IQ), and accuracy of noncontrast hybrid arterial spin labeling (NoHASL) magnetic resonance angiography (MRA) compared with time of flight (TOF) MRA and contrast-enhanced (CE) MRA in patients with known/suspected cerebrovascular ischemia. METHODS: Thirty inpatients were imaged at 1.5 T. Two neuroradiologists assessed 630 intracranial arterial segments for IQ (1, nondiagnostic; 3, satisfactory for diagnosis; and 5, excellent). Hemodynamically significant stenosis (>50%) was assessed against all combined techniques as reference. RESULTS: The NoHASL MRA IQ was diagnostic (3.32 ± 0.86) but affected by signal to noise ratio and spatial resolution limitations and significantly inferior to TOF (3.48 ± 0.68) and CE MRA (3.44 ± 0.78) (P < 0.0001 in both comparisons). Fourteen (2.2%) of 630 segments had hemodynamically significant stenoses at the reference standard. Sensitivity/specificity was not significantly different between techniques: NoHASL MRA, 67.9%/90.0%; TOF MRA, 67.9%/97.7%; and CE MRA, 50.0%/98.7%. CONCLUSIONS: The NoHASL MRA is feasible, with diagnostic quality imaging of proximal intracranial vessels. Low disease prevalence limited the assessment of technique accuracy.

Nonenhanced MR angiography of the pulmonary arteries using single-shot radial quiescent-interval slice-selective (QISS): a technical feasibility study.

BACKGROUND: For evaluation of the pulmonary arteries in patients suspected of pulmonary embolism, CT angiography (CTA) is the first-line imaging test with contrast-enhanced MR angiography (CEMRA) a potential alternative. Disadvantages of CTA include exposure to ionizing radiation and an iodinated contrast agent, while CEMRA is sensitive to respiratory motion and requires a gadolinium-based contrast agent. The primary goal of our technical feasibility study was to evaluate pulmonary arterial conspicuity using breath-hold and free-breathing implementations of a recently-developed nonenhanced approach, single-shot radial quiescent-interval slice-selective (QISS) MRA. METHODS: Breath-hold and free-breathing, navigator-gated versions of radial QISS MRA were evaluated at 1.5 Tesla in three healthy subjects and 11 patients without pulmonary embolism or arterial occlusion by CTA. Images were scored by three readers for conspicuity of the pulmonary arteries through the level of the segmental branches. In addition, one patient with pulmonary embolism was imaged. RESULTS: Scan time for a 54-slice acquisition spanning the pulmonary arteries was less than 2 minutes for breath-hold QISS, and less than 3.4 min using free-breathing QISS. Pulmonary artery branches through the segmental level were conspicuous with either approach. Free-breathing scans showed only mild blurring compared with breath-hold scans. For both readers, less than 1% of pulmonary arterial segments were rated as "not seen" for breath-hold and navigator-gated QISS, respectively. In subjects with atrial fibrillation, single-shot radial QISS consistently depicted the pulmonary artery branches, whereas navigator-gated 3D balanced steady-state free precession showed motion artifacts. In one patient with pulmonary embolism, radial QISS demonstrated central pulmonary emboli comparably to CEMRA and CTA. The thrombi were highly conspicuous on radial QISS images, but appeared subtle and were not prospectively identified on scout images acquired using a single-shot bSSFP acquisition. CONCLUSIONS: In this technical feasibility study, both breath-hold and free-breathing single-shot radial QISS MRA enabled rapid, consistent demonstration of the pulmonary arteries through the level of the segmental branches, with only minimal artifacts from respiratory motion and cardiac arrhythmias. Based on these promising initial results, further evaluation in patients with suspected pulmonary embolism appears warranted.

Apheresis as novel treatment for refractory angina with raised lipoprotein(a): a randomized controlled cross-over trial.

AIMS: To determine the clinical impact of lipoprotein apheresis in patients with refractory angina and raised lipoprotein(a) > 500 mg/L on the primary end point of quantitative myocardial perfusion, as well as secondary end points including atheroma burden, exercise capacity, symptoms, and quality of life. METHODS: We conducted a single-blinded randomized controlled trial in 20 patients with refractory angina and raised lipoprotein(a) > 500 mg/L, with 3 months of blinded weekly lipoprotein apheresis or sham, followed by crossover. The primary endpoint was change in quantitative myocardial perfusion reserve (MPR) assessed by cardiovascular magnetic resonance. Secondary endpoints included measures of atheroma burden, exercise capacity, symptoms and quality of life. RESULTS: The primary endpoint, namely MPR, increased following apheresis (0.47; 95% CI 0.31-0.63) compared with sham (-0.16; 95% CI - 0.33-0.02) yielding a net treatment increase of 0.63 (95% CI 0.37-0.89; P < 0.001 between groups). Improvements with apheresis compared with sham also occurred in atherosclerotic burden as assessed by total carotid wall volume (P < 0.001), exercise capacity by the 6 min walk test (P = 0.001), 4 of 5 domains of the Seattle angina questionnaire (all P < 0.02) and quality of life physical component summary by the short form 36 survey (P = 0.001). CONCLUSION: Lipoprotein apheresis may represent an effective novel treatment for patients with refractory angina and raised lipoprotein(a) improving myocardial perfusion, atheroma burden, exercise capacity and symptoms.

Accuracy of Noncontrast Quiescent-Interval Single-Shot Lower Extremity MR Angiography Versus CT Angiography for Diagnosis of Peripheral Artery Disease: Comparison With Digital Subtraction Angiography.

OBJECTIVES: This study sought to evaluate the image quality and diagnostic accuracy of noncontrast quiescent-interval single-shot (QISS) magnetic resonance angiography (MRA) versus iodine-contrast computed tomography angiography (CTA) in patients with peripheral artery disease (PAD), with invasive digital subtraction angiography (DSA) as the reference standard. BACKGROUND: QISS is a recently introduced noncontrast MRA technique. Although the diagnostic accuracy of QISS is reportedly similar to that of contrast-enhanced MRA, its performance compared with contrast-enhanced CTA, the most frequently used noninvasive modality for evaluation of PAD, is unknown. METHODS: Thirty patients (66 ± 7 years of age) with PAD underwent lower extremity CTA with third-generation dual-source dual-energy CT and 1.5-T MRA using a prototype noncontrast QISS sequence. DSA was performed within 50 days. The abdominal aorta and lower extremity run-off were imaged. Eighteen arterial segments were analyzed. Subjective image quality (3-point Likert scale) and stenosis (5-point grading) were evaluated by 2 observers and compared using the Mann-Whitney U and chi-square tests, respectively. Sensitivity and specificity of MRA and CTA for >50% stenosis detection were compared using the McNemar-test. RESULTS: Of 540 segments, 15 (2.8%) and 42 (7.8%) inconclusive segments were excluded from MRA and CTA analysis, respectively (p = 0.0006). The DSA results were available for 410 of the remaining segments. Overall subjective image quality was rated similarly with QISS-MRA (2.52 [95% confidence interval: 2.46 to 2.57]) and CTA (2.49 [95% confidence interval: 2.43 to 2.55]; p = 0.5062). The sensitivity and specificity of MRA for >50% stenosis were 84.9% and 97.2%, respectively, similar to those of CTA (87.3% and 95.4%, respectively). Interobserver agreement for stenosis detection was excellent for MRA (κ > 0.81) and CTA (κ > 0.81). CONCLUSIONS: Noncontrast QISS-MRA provides high diagnostic accuracy compared with DSA, while being less prone to image artifacts than CTA. QISS better visualizes heavily calcified segments with impaired flow. QISS-MRA obviates the need for contrast administration in PAD patients.

Global myocardial oedema in advanced decompensated heart failure.

AIMS: To use cardiac magnetic resonance (CMR) imaging with quantitative T2 mapping as surrogate for myocardial water content in patients with advanced decompensated heart failure (ADHF), compare these values with T2-values observed in chronic heart failure, and evaluate the change with decongestive therapy. METHODS AND RESULTS: Volumetric CMR measurements and quantitative T2 mapping were performed in 18 consecutive ADHF patients with clinical signs of volume overload. Eleven patients with stable heart failure were used as controls. Vasodilator therapy and diuretics were administered to achieve a pulmonary arterial wedge pressure (PAWP) of <18 mmHg and central venous pressure (CVP) of <12 mmHg, after which CMR was repeated. ADHF patients (62 ± 12 years; 89% male; left ventricular ejection fraction 23 ± 8%) presented with low cardiac index (2.08 ± 0.59 L/min/m2), high PAWP (25 ± 7 mmHg), and high CVP (14 ± 5 mmHg). After decongestion, the patients had a significant increase in cardiac index (+0.41 ± 0.53 L/min/m2; P = 0.005) and decreases in both PAWP (-9 ± 6 mmHg; P < 0.001) and CVP (-6 ± 5 mmHg; P < 0.001). At baseline, global left ventricular T2-values were higher in ADHF patients compared with controls (59.5 ± 4.6 vs. 54.7 ± 2.2 ms, respectively; P = 0.001). After decongestion, T2-values fell significantly to 55.9 ± 5.1 ms (P = 0.001), comparable with controls (P = 0.580). In contrast, psoas muscle T2-values were similar at baseline (38.6 ± 4.4 ms) vs. after decongestion (37.8 ± 4.8 ms; P = 0.397). Each 1 ms decrease in global left ventricular T2-value during decongestion was associated with a 1.14 ± 0.40 mmHg decrease in PAWP (P = 0.013), after correction for age and gender. CONCLUSION: Patients presenting with ADHF and volume overload have increased global left ventricular-but not psoas muscle-T2-values, which decrease with successful decongestion. Relief of myocardial oedema correlates with haemodynamic unloading.

MR imaging of iliofemoral peripheral vascular calcifications using proton density-weighted, in-phase three-dimensional stack-of-stars gradient echo.

PURPOSE: The presence of vascular calcifications helps to determine percutaneous access for interventional vascular procedures and has prognostic value for future cardiovascular events. Unlike CT, standard MRI techniques are insensitive to vascular calcifications. In this prospective study, we tested a proton density-weighted, in-phase (PDIP) three-dimensional (3D) stack-of-stars gradient-echo pulse sequence with approximately 1 mm3 isotropic spatial resolution at 1.5 Tesla (T) and 3T to detect iliofemoral peripheral vascular calcifications and correlated MR-determined lesion volumes with CT angiography (CTA). METHODS: The study was approved by the Institutional Review Board. The prototype PDIP stack-of-stars pulse sequence was applied in 12 patients with iliofemoral peripheral vascular calcifications who had undergone CTA. RESULTS: Vascular calcifications were well visualized in all subjects, excluding segments near prostheses or stents. The location, size, and shape of the calcifications were similar to CTA. Quantitative analysis showed excellent correlation (r2 = 0.84; P < 0.0001) between MR- and CT-based measures of calcification volume. In one subject in whom three pulse sequences were compared, PDIP stack-of-stars outperformed cartesian 3D gradient-echo and point-wise encoding time reduction with radial acquisition (PETRA). CONCLUSION: In this pilot study, a PDIP 3D stack-of-stars gradient-echo pulse sequence with high spatial resolution provided excellent image quality and accurately depicted the location and volume of iliofemoral vascular calcifications. Magn Reson Med 77:2146-2152, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

The diagnostic value of non-contrast enhanced quiescent interval single shot (QISS) magnetic resonance angiography at 3T for lower extremity peripheral arterial disease, in comparison to CT angiography.

BACKGROUND: The high incidence of renal insufficiency in patients with Peripheral Arterial Disease raises the concern for nephrogenic systemic fibrosis (NSF) with respect to contrast enhanced MRA. The risk of NSF is eliminated with non-contrast enhanced magnetic resonance angiography. The purpose of the current study is to compare image quality and diagnostic performance of non-contrast enhanced Quiescent Interval Single Shot (QISS) magnetic resonance angiography at 3 T versus CT angiography for evaluation of lower extremity Peripheral Arterial Disease (PAD). METHODS: 32 consecutive patients (23 male, 9 female, age range 40-81 years, average age 61.97 years) with clinically suspected lower extremity PAD underwent QISS MRA and CTA. 19 of 32 patients underwent Digital Subtraction Angiography (DSA). Image quality of MRA was compared with CTA by two radiologists with 10 and 8 years' experience according to a 4-point scale. The Kappa test was used to determine the intermodality agreement between MRA and CTA in stenosis assessment, and interobserver agreement with each method. Sensitivity and specificity of CTA and MRA in detecting hemodynamically significant stenosis (≥50 %) were compared, with DSA serving as reference standard when available. RESULTS: Image quality of QISS MRA was rated 3.70 ± 0.49 by reader 1, and 3.72 ± 0.47 by reader 2, significantly lower than that of CTA (3.80 ± 0.44 and 3.82 ± 0.42, P < 0.001 for both readers). Intermodality agreement between MRA and CTA was excellent for assessment of stenosis (Kappa = 0.923 ± 0.013 for reader 1, 0.930 ± 0.012 for reader 2). Interobserver agreement was 0.936 ± 0.012 for CTA and 0.935 ± 0.011 for MRA. For readers 1 and 2 respectively, the sensitivity of QISS was 94.25 and 93.26 % (versus 90.11 and 89.13 % for CTA, P > 0.05), and specificity of QISS was 96.70 and 97.75 % (versus 96.55 and 96.51 % for CTA, P > 0.05). For heavily calcified segments, sensitivity of QISS (95.83 and 95.83 %) was significantly higher than that of CTA (74.19 and 76.67 %, P < 0.05). CONCLUSION: QISS is a reliable alternative to CTA for evaluation of lower extremity PAD, and may be suitable as a first-line screening examination in patients with contraindications to intravenous contrast administration.

Improved dark blood imaging of the heart using radial balanced steady-state free precession.

BACKGROUND: Dark blood imaging of the heart is conventionally performed using a breath-hold, dual-inversion Cartesian fast spin-echo pulse sequence. Our aim was to develop a faster, more flexible approach that would be less motion-sensitive and provide better image quality. For this purpose, we implemented a prototype radial balanced steady-state free precession (bSSFP) pulse sequence. METHODS: The study was approved by the institutional review board. Six healthy volunteers and 27 subjects undergoing clinically-indicated cardiovascular magnetic resonance (CMR) were imaged using dark blood Cartesian fast spin-echo and radial bSSFP. For patient studies, overall image quality, fat suppression and blood nulling were scored on a 5-point Likert scale. The quality of visualization of the right and left ventricular free walls and septum were individually scored. Streaking and ghosting artifacts were noted, as well as signal dropout in the free wall of the left ventricle. RESULTS: In volunteer studies, radial bSSFP showed less degradation by cardiac or respiratory motion than fast spin-echo as indicated by visual analysis and calculation of the temporal signal-to-noise ratio. The least motion sensitivity and maximal imaging efficiency were achieved with a single-shot radial bSSFP acquisition using only 35 views (temporal resolution = 95 ms). In patient studies, radial bSSFP images showed fewer motion artifacts and were judged to provide better myocardial visibility, including depiction of the right ventricular free wall, than fast spin-echo. CONCLUSIONS: Dual-inversion radial bSSFP provides the benefits of diminished sensitivity to image artifacts from respiratory or cardiac motion, better myocardial visibility, and improved imaging efficiency compared with standard-of-care Cartesian fast spin-echo for dark blood imaging of the heart.

Magnetic resonance imaging phantoms for quality-control of myocardial T1 and ECV mapping: specific formulation, long-term stability and variation with heart rate and temperature.

BACKGROUND: Magnetic resonance imaging (MRI) phantoms are routinely used for quality assurance in MRI centres; however their long term stability for verification of myocardial T1/ extracellular volume fraction (ECV) mapping has never been investigated. METHODS: Nickel-chloride agarose gel phantoms were formulated in a reproducible laboratory procedure to mimic blood and myocardial T1 and T2 values, native and late after Gadolinium administration as used in T1/ECV mapping. The phantoms were imaged weekly with an 11 heart beat MOLLI sequence for T1 and long TR spin-echo sequences for T2, in a carefully controlled reproducible manner for 12 months. RESULTS: There were only small relative changes seen in all the native and post gadolinium T1 values (up to 9.0 % maximal relative change in T1 values) or phantom ECV (up to 8.3 % maximal relative change of ECV, up to 2.2 % maximal absolute change in ECV) during this period. All native and post gadolinium T2 values remained stable over time with <2 % change. Temperature sensitivity testing showed MOLLI T1 values in the long T1 phantoms increasing by 23.9 ms per degree increase and short T1 phantoms increasing by 0.3 ms per degree increase. There was a small absolute increase in ECV of 0.069 % (~0.22 % relative increase in ECV) per degree increase. Variation in heart rate testing showed a 0.13 % absolute increase in ECV (~0.45 % relative increase in ECV) per 10 heart rate increase. CONCLUSIONS: These are the first phantoms reported in the literature modeling T1 and T2 values for blood and myocardium specifically for the T1mapping/ECV mapping application, with stability tested rigorously over a 12 month period. This work has significant implications for the utility of such phantoms in improving the accuracy of serial scans for myocardial tissue characterisation by T1 mapping methods and in multicentre work.

Arterial spin labeled carotid MR angiography: A phantom study examining the impact of technical and hemodynamic factors.

PURPOSE: To quantify the accuracy of three-dimensional (3D) radial arterial spin labeled (ASL) magnetic resonance angiography (MRA) using vascular models of carotid stenosis. METHODS: Eight vascular models were imaged at 1.5 Tesla using pulsatile flow waveforms at rates found in the internal carotid arteries (100-400 mL/min). The impacts of the 3D ASL imaging readout (fast low angle shot (FLASH) versus balanced steady-state free precession (bSSFP)), ultrashort echo time imaging using a pointwise encoding time reduction with radial acquisition (PETRA), and model stenosis severity on the accuracy of vascular model display at the location of stenosis were quantified. Accuracy was computed vis-à-vis a reference bSSFP volume acquired under no flow. Comparisons were made with standard-of-care contrast-enhanced MRA (CEMRA) and Cartesian time-of-flight (TOF) MRA protocols. RESULTS: For 50% and 70% stenoses, CEMRA was most accurate (respective accuracies of 81.7% and 78.6%), followed by ASL FLASH (75.7% and 71.8%), ASL PETRA (69.6% and 70.6%), 3D TOF (66.6% and 57.1%), ASL bSSFP (68.7% and 51.2%), and 2D TOF (65.1% and 50.6%). CONCLUSION: Flow phantom imaging studies show that ASL MRA can improve the display of hemodynamically significant carotid arterial stenosis compared with TOF MRA, with FLASH and ultrashort echo time readouts being most accurate.

Quiescent interval low angle shot magnetic resonance angiography of the extracranial carotid arteries.

PURPOSE: To test the feasibility of a quiescent interval low-angle shot (QLASH) sequence for nonenhanced MR angiography (MRA) of the extracranial carotid arteries at 3 T. METHODS: The extracranial carotid arteries were imaged using QLASH MRA in healthy volunteers and patients with carotid arterial disease. The impact of three gating strategies (electrocardiographic-gated, pulse-gated, ungated) was evaluated. Image quality comparisons were made with respect to two-dimensional (2D) time of flight (TOF) MRA in volunteers and patients and contrast-enhanced MRA (CEMRA) in patients. Stenoses in patients were graded. RESULTS: QLASH MRA displayed the entire extent of the extracranial carotid arteries from their origins to the skull base. Electrocardiographic-gated QLASH MRA provided better image quality than pulse-gated and ungated implementations (P < 0.05) as well as 2D TOF MRA (P < 0.05). For grading of disease, QLASH MRA showed almost perfect agreement with CEMRA (Cohen's kappa = 0.86, P < 0.001) in a small cohort of patients with carotid arterial stenosis. CONCLUSION: QLASH MRA allows for evaluation of the entire extent of the extracranial carotid arteries with an average scan time of less than 6 min and better image quality than 2D TOF. Initial clinical results in this pilot study suggest that QLASH has potential utility as a nonenhanced alternative to CEMRA.