Visualizing wall enhancement over time in unruptured intracranial aneurysms using 3D vessel wall imaging.

BACKGROUND: Few studies directed at assessing the visualization of the walls of unruptured aneurysms have used higher-resolution 3D MRI vessel wall imaging. Prospective longitudinal studies are also needed to screen vessel wall changes in unruptured aneurysms. PURPOSE: To compare the aneurysm wall visualization on pre- and post-3D isotropic T1 -weighted Sampling Perfection with Application-optimized Contrasts by using different flip angle Evolutions (SPACE) images and to explore whether there is a change in wall enhancement at follow up. STUDY TYPE: Prospective. POPULATION: Twenty-nine patients with a total of 35 unruptured intracranial aneurysms. SEQUENCE: 3D T1 -weighted pre- and postcontrast SPACE (0.5 mm isotropic) at 3.0T. ASSESSMENT: The aneurysm wall visibility (0-5 scale) between pre- and postcontrast images as well as the wall enhancement (0-5 scale) between follow-up and baseline studies (6-30 months, average 12.7 months) were compared. Differences in wall visibility and enhancement were also investigated as a function of aneurysm diameter and location. STATISTICAL TEST: The Wilcoxon signed rank paired test was used to compare the wall visibility score between pre- and postcontrast SPACE images, as well as wall enhancement between follow-up and baseline. The Mann-Whitney and Kruskal-Wallis tests were used to investigate the enhancement difference between different diameters and locations. RESULTS: Postcontrast images had significantly higher wall visibility (P = 0.01). A wall enhancement score ≥2 was found in 71% of the aneurysms. Changes in levels of wall enhancement were found in 17% of the aneurysms at follow-up studies, but those changes were small. Wall visibility and enhancement scores of large aneurysms were significantly higher than small ones (P < 0.001). DATA CONCLUSION: 3D T1 -weighted higher resolution SPACE can be used to assess changes in enhancement at follow-up studies. Contrast SPACE image provides better aneurysm wall visibility and improves visualization of the aneurysm wall. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019;50:193-200.

Assessment of Reynolds stress components and turbulent pressure loss using 4D flow MRI with extended motion encoding.

PURPOSE: To measure the Reynolds stress tensor using 4D flow MRI, and to evaluate its contribution to computed pressure maps. METHODS: A method to assess both velocity and Reynolds stress using 4D flow MRI is presented and evaluated. The Reynolds stress is compared by cross-sectional integrals of the Reynolds stress invariants. Pressure maps are computed using the pressure Poisson equation-both including and neglecting the Reynolds stress. RESULT: Good agreement is seen for Reynolds stress between computational fluid dynamics, simulated MRI, and MRI experiment. The Reynolds stress can significantly influence the computed pressure loss for simulated (eg, -0.52% vs -15.34% error; P < 0.001) and experimental (eg, 306 ± 11 vs 203 ± 6 Pa; P < 0.001) data. A 54% greater pressure loss is seen at the highest experimental flow rate when accounting for Reynolds stress (P < 0.001). CONCLUSION: 4D flow MRI with extended motion-encoding enables quantification of both the velocity and the Reynolds stress tensor. The additional information provided by this method improves the assessment of pressure gradients across a stenosis in the presence of turbulence. Unlike conventional methods, which are only valid if the flow is laminar, the proposed method is valid for both laminar and disturbed flow, a common presentation in diseased vessels. Magn Reson Med 79:1962-1971, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Highly accelerated intracranial 4D flow MRI: evaluation of healthy volunteers and patients with intracranial aneurysms.

OBJECTIVES: To evaluate an accelerated 4D flow MRI method that provides high temporal resolution in a clinically feasible acquisition time for intracranial velocity imaging. MATERIALS AND METHODS: Accelerated 4D flow MRI was developed by using a pseudo-random variable-density Cartesian undersampling strategy (CIRCUS) with the combination of k-t, parallel imaging and compressed sensing image reconstruction techniques (k-t SPARSE-SENSE). Four-dimensional flow data were acquired on five healthy volunteers and eight patients with intracranial aneurysms using CIRCUS (acceleration factor of R = 4, termed CIRCUS4) and GRAPPA (R = 2, termed GRAPPA2) as the reference method. Images with three times higher temporal resolution (R = 12, CIRCUS12) were also reconstructed from the same acquisition as CIRCUS4. Qualitative and quantitative image assessment was performed on the images acquired with different methods, and complex flow patterns in the aneurysms were identified and compared. RESULTS: Four-dimensional flow MRI with CIRCUS was achieved in 5 min and allowed further improved temporal resolution of <30 ms. Volunteer studies showed similar qualitative and quantitative evaluation obtained with the proposed approach compared to the reference (overall image scores: GRAPPA2 3.2 ± 0.6; CIRCUS4 3.1 ± 0.7; CIRCUS12 3.3 ± 0.4; difference of the peak velocities: -3.83 ± 7.72 cm/s between CIRCUS4 and GRAPPA2, -1.72 ± 8.41 cm/s between CIRCUS12 and GRAPPA2). In patients with intracranial aneurysms, the higher temporal resolution improved capturing of the flow features in intracranial aneurysms (pathline visualization scores: GRAPPA2 2.2 ± 0.2; CIRCUS4 2.5 ± 0.5; CIRCUS12 2.7 ± 0.6). CONCLUSION: The proposed rapid 4D flow MRI with a high temporal resolution is a promising tool for evaluating intracranial aneurysms in a clinically feasible acquisition time.

Accelerated whole brain intracranial vessel wall imaging using black blood fast spin echo with compressed sensing (CS-SPACE).

OBJECTIVE: Develop and optimize an accelerated, high-resolution (0.5 mm isotropic) 3D black blood MRI technique to reduce scan time for whole-brain intracranial vessel wall imaging. MATERIALS AND METHODS: A 3D accelerated T1-weighted fast-spin-echo prototype sequence using compressed sensing (CS-SPACE) was developed at 3T. Both the acquisition [echo train length (ETL), under-sampling factor] and reconstruction parameters (regularization parameter, number of iterations) were first optimized in 5 healthy volunteers. Ten patients with a variety of intracranial vascular disease presentations (aneurysm, atherosclerosis, dissection, vasculitis) were imaged with SPACE and optimized CS-SPACE, pre and post Gd contrast. Lumen/wall area, wall-to-lumen contrast ratio (CR), enhancement ratio (ER), sharpness, and qualitative scores (1-4) by two radiologists were recorded. RESULTS: The optimized CS-SPACE protocol has ETL 60, 20% k-space under-sampling, 0.002 regularization factor with 20 iterations. In patient studies, CS-SPACE and conventional SPACE had comparable image scores both pre- (3.35 ± 0.85 vs. 3.54 ± 0.65, p = 0.13) and post-contrast (3.72 ± 0.58 vs. 3.53 ± 0.57, p = 0.15), but the CS-SPACE acquisition was 37% faster (6:48 vs. 10:50). CS-SPACE agreed with SPACE for lumen/wall area, ER measurements and sharpness, but marginally reduced the CR. CONCLUSION: In the evaluation of intracranial vascular disease, CS-SPACE provides a substantial reduction in scan time compared to conventional T1-weighted SPACE while maintaining good image quality.

High resolution imaging of the intracranial vessel wall at 3 and 7 T using 3D fast spin echo MRI.

OBJECTIVES: High resolution MRI of the intracranial vessel wall provides important insights in the assessment of intracranial vascular disease. This study aims to refine high resolution 3D MRI techniques for intracranial vessel wall imaging at both 3 and 7 T using customized flip angle train design, and to explore their comparative abilities. MATERIALS AND METHODS: 11 patients with intracranial artery disease (four atherosclerotic plaques, six aneurysms and one reversible cerebral vasoconstriction syndrome) were imaged at 3 and 7 T with a 3D T 1-weighted fast-spin-echo sequence (SPACE) both pre and post Gd contrast injection. Wall to lumen contrast ratio (CRwall-lumen), contrast enhancement ratio (ER) and the sharpness of the vessel wall were quantified. Two experienced radiologists evaluated the image quality on a 0-5 scale. RESULTS: Both 3 and 7 T achieved good image quality with high resolution (nominal 0.5 mm isotropic) and whole brain coverage. The CRwall-lumen and the ER measurements were comparable (p > 0.05). The 7 T images were significantly sharper (sharpness: 2.69 ± 0.50 vs. 1.88 ± 0.53 mm(-1), p < 0.001) with higher image quality (reader 1 score: 3.5 ± 1.1 vs. 2.4 ± 1.1, p = 0.002) compared to 3 T. CONCLUSIONS: 3D T 1-weighted SPACE can be used for intracranial vessel wall evaluation at both 3 and 7 T. 7 T provides significantly better image quality and improves the confidence of diagnosis.

Adaptive online self-gating (ADIOS) for free-breathing noncontrast renal MR angiography.

PURPOSE: To develop a respiratory self-gating method, adaptive online self-gating (ADIOS), for noncontrast MR angiography (NC MRA) of renal arteries to overcome some limitations of current free-breathing methods. METHODS: A NC MRA pulse sequence for online respiratory self-gating was developed based on three-dimensional balanced steady-state free precession (bSSFP) and slab-selective inversion-recovery. Motion information was derived directly from the slab being imaged for online gating. Scan efficiency was maintained by an automatic adaptive online algorithm. Qualitative and quantitative assessments of image quality were performed and results were compared with conventional diaphragm navigator (NAV). RESULTS: NC MRA imaging was successfully completed in all subjects (n = 15). Similarly good image quality was observed in the proximal-middle renal arteries with ADIOS compared with NAV. Superior image quality was observed in the middle-distal renal arteries in the right kidneys with no NAV-induced artifacts. Maximal visible artery length was significantly longer with ADIOS versus NAV in the right kidneys. NAV setup was completely eliminated and scan time was significantly shorter with ADIOS on average compared with NAV. CONCLUSION: The proposed ADIOS technique for noncontrast MRA provides high-quality visualization of renal arteries with no diaphragm navigator-induced artifacts, simplified setup, and shorter scan time.

Reducing view-sharing using compressed sensing in time-resolved contrast-enhanced magnetic resonance angiography.

PURPOSE: To study temporal and spatial blurring artifacts from k-space view-sharing in time-resolved MR angiography (MRA) and to propose a technique for reducing these artifacts. METHODS: We acquired k-space data sets using a three-dimensional time-resolved MRA view-sharing sequence and retrospectively reformatted them into two reconstruction frameworks: full view-sharing via time-resolved imaging with stochastic trajectories (TWIST) and minimal k-space view-sharing and compressed sensing (CS-TWIST). The two imaging series differed in temporal footprint but not in temporal frame rate. The artifacts from view-sharing were compared qualitatively and quantitatively in nine patients in addition to a phantom experiment. RESULTS: CS-TWIST was able to reduce the imaging temporal footprint by two- to three-fold compared with TWIST, and the overall subjective image quality of CS-TWIST was higher than that for TWIST (P < 0.05). View sharing caused a delay in the visualization of small blood vessels, and the mean transit time of the carotid artery calculated based on TWIST reconstruction was 0.6 s longer than that for CS-TWIST (P < 0.01). In thoracic MRA, the shorter temporal footprint decreased the sensitivity to physiological motion blurring, and vessel sharpness was improved by 8.8% ± 6.0% using CS-TWIST (P < 0.05). CONCLUSION: In time-resolved MRA, the longer temporal footprint due to view-sharing causes spatial and temporal artifacts. CS-TWIST is a promising method for reducing these artifacts.

2D phase-sensitive inversion recovery imaging to measure in vivo spinal cord gray and white matter areas in clinically feasible acquisition times.

PURPOSE: To present and assess a procedure for measurement of spinal cord total cross-sectional areas (TCA) and gray matter (GM) areas based on phase-sensitive inversion recovery imaging (PSIR). In vivo assessment of spinal cord GM and white matter (WM) could become pivotal to study various neurological diseases, but it is challenging because of insufficient GM/WM contrast provided by conventional magnetic resonance imaging (MRI). MATERIALS AND METHODS: We acquired 2D PSIR images at 3T at each disc level of the spinal axis in 10 healthy subjects and measured TCA, cord diameters, WM and GM areas, and GM area/TCA ratios. Second, we investigated 32 healthy subjects at four selected levels (C2-C3, C3-C4, T8-T9, T9-T10, total acquisition time <8 min) and generated normative reference values of TCA and GM areas. We assessed test-retest, intra- and interoperator reliability of the acquisition strategy, and measurement steps. RESULTS: The measurement procedure based on 2D PSIR imaging allowed TCA and GM area assessments along the entire spinal cord axis. The tests we performed revealed high test-retest/intraoperator reliability (mean coefficient of variation [COV] at C2-C3: TCA = 0.41%, GM area = 2.75%) and interoperator reliability of the measurements (mean COV on the 4 levels: TCA = 0.44%, GM area = 4.20%; mean intraclass correlation coefficient: TCA = 0.998, GM area = 0.906). CONCLUSION: 2D PSIR allows reliable in vivo assessment of spinal cord TCA, GM, and WM areas in clinically feasible acquisition times. The area measurements presented here are in agreement with previous MRI and postmortem studies.

High spatial and temporal resolution dynamic contrast-enhanced magnetic resonance angiography using compressed sensing with magnitude image subtraction.

PURPOSE: We propose a compressed-sensing (CS) technique based on magnitude image subtraction for high spatial and temporal resolution dynamic contrast-enhanced MR angiography (CE-MRA). METHODS: Our technique integrates the magnitude difference image into the CS reconstruction to promote subtraction sparsity. Fully sampled Cartesian 3D CE-MRA datasets from 6 volunteers were retrospectively under-sampled and three reconstruction strategies were evaluated: k-space subtraction CS, independent CS, and magnitude subtraction CS. The techniques were compared in image quality (vessel delineation, image artifacts, and noise) and image reconstruction error. Our CS technique was further tested on seven volunteers using a prospectively under-sampled CE-MRA sequence. RESULTS: Compared with k-space subtraction and independent CS, our magnitude subtraction CS provides significantly better vessel delineation and less noise at 4× acceleration, and significantly less reconstruction error at 4× and 8× (P < 0.05 for all). On a 1-4 point image quality scale in vessel delineation, our technique scored 3.8 ± 0.4 at 4×, 2.8 ± 0.4 at 8×, and 2.3 ± 0.6 at 12× acceleration. Using our CS sequence at 12× acceleration, we were able to acquire dynamic CE-MRA with higher spatial and temporal resolution than current clinical TWIST protocol while maintaining comparable image quality (2.8 ± 0.5 vs. 3.0 ± 0.4, P = NS). CONCLUSION: Our technique is promising for dynamic CE-MRA.

High-resolution diffusion-weighted imaging for the separation of benign from malignant BI-RADS 4/5 lesions found on breast MRI at 3T.

PURPOSE: To determine whether readout-segmented echo-planar diffusion imaging (RESOLVE) improves separation of malignant versus benign lesions compared to standard single-shot echo-planar imaging (ss-EPI) on BI-RADS 4/5 lesions detected on breast magnetic resonance imaging (MRI). MATERIALS AND METHODS: Consecutive 3T breast MRI studies with BI-RADS 4/5 designation and subsequent biopsy or benign mastectomy were retrospectively identified. Freehand regions of interest (ROIs) were drawn on lesions and also on normal background fibroglandular tissue for comparison. Lesion-to-background contrast was evaluated by normalizing signal intensity of the lesion ROI by the normal background tissue ROI at b = 800. Statistical analysis used the Mann-Whitney/Wilcoxon rank-sum test for unpaired and Wilcoxon signed-rank for paired comparisons. RESULTS: Of 38 lesions in 32 patients, 10 were malignant. Lesion-to-background contrast was higher on RESOLVE than ss-EPI (1.80 ± 0.71 vs. 1.62 ± 0.63, P = 0.03). Mean apparent diffusion coefficient (ADC) was the same or lower on RESOLVE than ss-EPI, and this effect was largest in malignant lesions (RESOLVE 0.90 ± 0.13; ss-EPI 1.00 ± 0.13; median difference -0.10 (95% confidence interval [CI]: -0.17, -0.02) × 10(-3) mm(2) /sec; P = 0.014). By either diffusion method, there was a statistically significant difference between benign and malignant mean ADC (P < 0.001). CONCLUSION: Increased lesion-to-background contrast and improved separation of benign from malignant lesions by RESOLVE compared to standard diffusion suggests that RESOLVE may show promise as an adjunct to clinical breast MRI.

Multi-contrast atherosclerosis characterization (MATCH) of carotid plaque with a single 5-min scan: technical development and clinical feasibility.

BACKGROUND: Multi-contrast weighted imaging is a commonly used cardiovascular magnetic resonance (CMR) protocol for characterization of carotid plaque composition. However, this approach is limited in several aspects including low slice resolution, long scan time, image mis-registration, and complex image interpretation. In this work, a 3D CMR technique, named Multi-contrast Atherosclerosis Characterization (MATCH), was developed to mitigate the above limitations. METHODS: MATCH employs a 3D spoiled segmented fast low angle shot readout to acquire data with three different contrast weightings in an interleaved fashion. The inherently co-registered image sets, hyper T1-weighting, gray blood, and T2-weighting, are used to detect intra-plaque hemorrhage (IPH), calcification (CA), lipid-rich necrotic core (LRNC), and loose-matrix (LM). The MATCH sequence was optimized by computer simulations and testing on four healthy volunteers and then evaluated in a pilot study of six patients with carotid plaque, using the conventional multi-contrast protocol as a reference. RESULTS: On MATCH images, the major plaque components were easy to identify. Spatial co-registration between the three image sets with MATCH was particularly helpful for the reviewer to discern co-existent components in an image and appreciate their spatial relation. Based on Cohen's kappa tests, moderate to excellent agreement in the image-based or artery-based component detection between the two protocols was obtained for LRNC, IPH, CA, and LM, respectively. Compared with the conventional multi-contrast protocol, the MATCH protocol yield significantly higher signal contrast ratio for IPH (3.1±1.3 vs. 0.4±0.3, p<0.001) and CA (1.6±1.5 vs. 0.7±0.6, p=0.012) with respect to the vessel wall. CONCLUSIONS: To the best of our knowledge, the proposed MATCH sequence is the first 3D CMR technique that acquires spatially co-registered multi-contrast image sets in a single scan for characterization of carotid plaque composition. Our pilot clinical study suggests that the MATCH-based protocol may outperform the conventional multi-contrast protocol in several respects. With further technical improvements and large-scale clinical validation, MATCH has the potential to become a CMR method for assessing the risk of plaque disruption in a clinical workup.

Low-dose 3D time-resolved magnetic resonance angiography (MRA) of the supraaortic arteries: correlation with high spatial resolution 3D contrast-enhanced MRA.

PURPOSE: To evaluate the feasibility of low-dose, 3D time-resolved contrast-enhanced magnetic resonance angiography (TR-CEMRA) in the assessment of the supraaortic vessel, and to compare the results with high-resolution contrast-enhanced MRA (HR-CEMRA). MATERIALS AND METHODS: This was an Institutional Review Board-approved retrospective study. Forty-five consecutive patients underwent contrast-enhanced 3D TR-CEMRA and 3D HR-CEMRA for evaluation of neurovascular disease at 3.0 T. Gadobutrol was administered at a constant dose of 1 mL for TR-CEMRA (independent of patient weight), and 0.1 mmol/kg for HR-CEMRA. Two readers evaluated image quality using a four-point scale (from 0 = excellent to 3 = nondiagnostic), and subsequently graded each stenosis into clinically relevant categories: normal (0%), mild stenosis (<50%), moderate to severe (>50%), and occlusion. RESULTS: The overall image quality for low-dose TR-CEMRA was in the diagnostic range (median 0, range 0-3). On the grading of stenosis, TR-CEMRA using the TWIST sequence correlated with HR-CEMRA (r = 0.668, P < 0.001). In terms of the comparison of TR-CEMRA with HR-CEMRA, of the 675 supraaortic arterial segments evaluated for stenosis or occlusion, agreement occurred in 611 of 675 (90.5%), overestimation in 41 of 675 (6.1%), and underestimation 23 of 675 (3.4%). CONCLUSION: TR-CEMRA achieved by administration of a small contrast dose (1 cc) yields rapid and important functional and anatomical information in the evaluation of supraaortic arteries. Due to limited spatial resolution, TR-CEMRA at the current parameters has a tendency to overestimate the stenosis of smaller intracranial arteries compared to HR-CEMRA.

Pretreatment evaluation of peripheral vascular malformations using low-dose contrast-enhanced time-resolved 3D MR angiography: initial results in 22 patients.

OBJECTIVE: The objective of our study was to assess the feasibility and diagnostic performance of time-resolved MR angiography (MRA) in the pretreatment evaluation of peripheral vascular malformations at 1.5 T. SUBJECTS AND METHODS: Twenty-two consecutive patients (15 women and seven men; mean age, 22.1 ± 12.1 years) who were known or suspected to have vascular malformations were studied using time-resolved MRA with interleaved stochastic trajectories and parallel acquisition followed by conventional MRA (n = 12). All studies were performed on a 1.5-T whole-body MR system. Image sets of time-resolved and conventional MRA were independently reviewed by two observers for image quality, level of confidence and presence, location, and classification of vascular malformations. The interobserver agreement was calculated using conventional MRA as the standard of reference. RESULTS: On the basis of time-resolved MRA, nine of the lesions were categorized as high-flow arteriovenous malformations (AVMs), the remaining 13 lesions were categorized as low-flow vascular malformations or hemangiomas. There was no significant difference in the image quality grading scores between the two observers for time-resolved MRA (p = 0.61) and conventional MRA (p = 0.54). The kappa coefficient revealed good agreement (κ = 0.76) between time-resolved MRA and conventional MRA. Both observers visualized fine vascular details with higher confidence in two patients on conventional MRA. The additional functional information regarding feeding artery and flow patterns provided by time-resolved MRA was confirmed by digital subtraction in all nine cases. CONCLUSION: Time-resolved MRA provided the temporal information needed for the appropriate classification of vascular malformations, enabling visualization of both the arterial feeders and draining veins. Furthermore, time-resolved MRA has the potential to be used as an initial and screening diagnostic tool obviating conventional MRA to categorize these lesions and determine their extent to correctly guide treatment.

Time-resolved lower extremity MRA with temporal interpolation and stochastic spiral trajectories: preliminary clinical experience.

PURPOSE: To assess added value of a new time-resolved technique with temporal interpolation and stochastic spiral trajectory through k-space and parallel imaging (TR-MRA) to conventional bolus chase MRA (BC-MRA) for infragenual peripheral artery evaluation. MATERIALS AND METHODS: An institutional review board-approved retrospective review of peripheral arterial disease patients was performed. Infragenual TR-MRA and BC-MRA were performed in 26 patients over four months. Two readers individually assessed image quality, diagnostic confidence, and stenosis severity and length in 13 defined below knee segments, first with BC-MRA alone, and then with a combined BC-MRA and TR-MRA reading (BC+TR-MRA). Perceived contribution of TR-MRA was rated by each reader. The reference standard was a consensus reading of both sequences. Catheter angiographic (CA) correlation was available in 6 patients. RESULTS: A total of 646 infragenual segments in 51 extremities were evaluated. Image quality and diagnostic confidence were superior for BC+TR-MRA compared with BC-MRA alone (P < 0.001). Adding TR-MRA improved sensitivity (85.7% versus 80.7%; P < 0.05) and diagnostic accuracy (88.1% versus 85.4%; P < 0.05) for hemodynamically significant stenosis. Venous contamination (0% versus 13.1% segments) and motion (0.9% versus 8.0%) were decreased for BC+TR-MRA versus BC-MRA alone, P < 0.01. For BC+TR-MRA, TR-MRA was rated more useful than BC-MRA in 30/51 legs (58.8%). TR-MRA identified retrograde flow in 5 segments. Where available, there was high concordance between CA and BC+TR-MRA (91.6%) for stenosis. CONCLUSION: Adding TR-MRA with temporal interpolation and stochastic spiral trajectories to bolus chase MRA improves image quality, diagnostic confidence and accuracy. It provides hemodynamic information and minimizes venous contamination and patient motion.

Image quality and diagnostic accuracy of unenhanced SSFP MR angiography compared with conventional contrast-enhanced MR angiography for the assessment of thoracic aortic diseases.

OBJECTIVES: The purpose of this study was to determine the image quality and diagnostic accuracy of three-dimensional (3D) unenhanced steady state free precession (SSFP) magnetic resonance angiography (MRA) for the evaluation of thoracic aortic diseases. METHODS: Fifty consecutive patients with known or suspected thoracic aortic disease underwent free-breathing ECG-gated unenhanced SSFP MRA with non-selective radiofrequency excitation and contrast-enhanced (CE) MRA of the thorax at 1.5 T. Two readers independently evaluated the two datasets for image quality in the aortic root, ascending aorta, aortic arch, descending aorta, and origins of supra-aortic arteries, and for abnormal findings. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were determined for both datasets. Sensitivity, specificity, and diagnostic accuracy of unenhanced SSFP MRA for the diagnosis of aortic abnormalities were determined. RESULTS: Abnormal aortic findings, including aneurysm (n = 47), coarctation (n = 14), dissection (n = 12), aortic graft (n = 6), intramural hematoma (n = 11), mural thrombus in the aortic arch (n = 1), and penetrating aortic ulcer (n = 9), were confidently detected on both datasets. Sensitivity, specificity, and diagnostic accuracy of SSFP MRA for the detection of aortic disease were 100% with CE-MRA serving as a reference standard. Image quality of the aortic root was significantly higher on SSFP MRA (P < 0.001) with no significant difference for other aortic segments (P > 0.05). SNR and CNR values were higher for all segments on SSFP MRA (P < 0.01). CONCLUSION: Our results suggest that free-breathing navigator-gated 3D SSFP MRA with non-selective radiofrequency excitation is a promising technique that provides high image quality and diagnostic accuracy for the assessment of thoracic aortic disease without the need for intravenous contrast material.

Optimal k-space sampling for dynamic contrast-enhanced MRI with an application to MR renography.

For time-resolved acquisitions with k-space undersampling, a simulation method was developed for selecting imaging parameters based on minimization of errors in signal intensity versus time and physiologic parameters derived from tracer kinetic analysis. Optimization was performed for time-resolved angiography with stochastic trajectories (TWIST) algorithm applied to contrast-enhanced MR renography. A realistic 4D phantom comprised of aorta and two kidneys, one healthy and one diseased, was created with ideal tissue time-enhancement pattern generated using a three-compartment model with fixed parameters, including glomerular filtration rate (GFR) and renal plasma flow (RPF). TWIST acquisitions with different combinations of sampled central and peripheral k-space portions were applied to this phantom. Acquisition performance was assessed by the difference between simulated signal intensity (SI) and calculated GFR and RPF and their ideal values. Sampling of the 20% of the center and 1/5 of the periphery of k-space in phase-encoding plane and data-sharing of the remaining 4/5 minimized the errors in SI (<5%), RPF, and GFR (both <10% for both healthy and diseased kidneys). High-quality dynamic human images were acquired with optimal TWIST parameters and 2.4 sec temporal resolution. The proposed method can be generalized to other dynamic contrast-enhanced MRI applications, e.g., MR angiography or cancer imaging.

Time-resolved MR angiography in the evaluation of central thoracic venous occlusive disease.

OBJECTIVE: The objective of our study was to assess the feasibility and diagnostic performance of time-resolved MR angiography (MRA) in the evaluation of central thoracic venous occlusive disease and to compare time-resolved MRA with conventional MRA and catheter angiography. MATERIALS AND METHODS: Twenty patients (eight women and 12 men; age range, 19-74 years) with suspected central thoracic venous occlusive disease underwent time-resolved MRA using time-resolved angiography with interleaved stochastic trajectories (TWIST) and parallel acquisition, followed by conventional MRA. Catheter angiography was performed within 1-14 days after MRA and was available for a total of 60 segments for correlation. Time-resolved and conventional MRA images were evaluated in separate reading sessions by two independent radiologists for image quality and level of confidence and degree of venoocclusive disease. The interobserver and intermodality agreement, sensitivity, and specificity were calculated using catheter angiography as the standard of reference. RESULTS: Time-resolved MRA resulted in diagnostic-quality images that did not differ significantly in quality compared with conventional MRA. Thirty-one segmental venous stenoses were identified. The kappa coefficient revealed moderate intermodality agreement (kappa = 0.54; 95% CI, 0.32-0.76) between time-resolved MRA and conventional MRA. When compared with catheter angiography, the sensitivity and specificity for the diagnosis of significant stenosis (> or = 70%) were 87.5% and 68% for time-resolved MRA and 90% and 90% for conventional MRA, respectively. CONCLUSION: Time-resolved MRA, as described in this study, has the potential to be used as an initial and screening diagnostic tool obviating conventional MRA and its associated higher contrast dose in normal and near-normal examinations. However, because of its relatively lower specificity, adjunct use of conventional MRA is still required for accurate grading of venous occlusive disease.

Isovolumic cardiac contraction on high-temporal-resolution cine MR images: study in heart failure patients and healthy volunteers.

PURPOSE: To prospectively implement high-temporal-resolution cine magnetic resonance (MR) imaging protocol to compare cardiac preejection contraction (PEC) and prefilling relaxation (PFR) times between heart failure (HF) patients and healthy control subjects and to assess accuracy of PEC times to stratify HF patients, with ejection fraction (EF) and New York Heart Association (NYHA) symptom class as reference standards. MATERIALS AND METHODS: Following institutional review board approval of this HIPAA-compliant study and written informed consent, 18 healthy volunteers (10 women, eight men; mean age, 43 years +/- 14 [standard deviation]) and 18 HF patients (five women, 13 men; mean age, 49.8 years +/- 3) were imaged (breath-hold true fast imaging with steady-state precession, with temporal resolution of 5.6 msec at 1.5 T). By using left ventricular (LV) outflow tract acquisition, PEC phase was defined as time at QRS trigger to immediately before aortic valve opening. PFR was defined as time from initial aortic valve closure to immediately before mitral valve opening. Group means were compared (unpaired Student t test). Accuracy of PEC parameters in stratifying participants with severe systolic HF on the basis of EF and NYHA symptom class was assessed (receiver operating characteristic curve analysis). RESULTS: Compared with control subjects, HF patients had prolonged mean PEC time (40.4 msec +/- 11.8 vs 91.3 msec +/- 26, P < .001) and mean PFR time (68.3 msec +/- 26.8 vs 103.7 msec +/- 41.8, P < .01). PEC time correlated with global EF (r = -0.73, P < .001) and LV mass (r = 0.69, P < .001). For identification of patients with severe LV systolic dysfunction (EF 2), PEC time had good accuracy (AUC, 0.875 [P < .001]). CONCLUSION: It is feasible to assess isovolumic PEC and PFR phases of the cardiac cycle with high-frame-rate cine MR images, and PEC time is a surrogate measure of moderate-to-severe systolic HF.

Isotropic high-spatial-resolution contrast-enhanced 3.0-T MR angiography in patients suspected of having renal artery stenosis.

The purpose of this study was to prospectively evaluate the diagnostic performance of contrast material-enhanced magnetic resonance (MR) angiography performed at 3 T for assessment of renal artery stenosis (RAS) by using parallel acquisition techniques with high acceleration factors and with digital subtraction angiography (DSA) as the reference standard. The study was institutional review board approved, and written informed consent was obtained from all patients. Twenty-nine patients (18 men, 11 women; mean age, 57.1 years +/- 14.3 [standard deviation]) suspected of having RAS underwent MR angiography. Images were evaluated qualitatively and quantitatively. The interobserver variability, sensitivity, specificity, and positive and negative predictive values of 3-T MR angiography, as compared with DSA (performed in 15 patients), were calculated. All examinations yielded good or excellent image quality. The sensitivity and specificity of MR angiography in grading significant (>75%) stenosis were 94% and 96%, respectively. Owing to its high sensitivity, contrast-enhanced 3-T MR angiography can be used reliably to exclude RAS and can serve as a useful screening method in the diagnostic work-up of patients with arterial hypertension.

Noncontrast 3D steady state free precession magnetic resonance angiography of the thoracic central veins using nonselective radiofrequency excitation over a large field of view: initial experience.

PURPOSE: To evaluate the feasibility of three-dimensional (3D) steady state free precession (SSFP) magnetic resonance angiography (MRA) using nonselective radiofrequency excitation for the assessment of thoracic central veins. MATERIALS AND METHODS: Thirty consecutive patients (17 males, 13 females, age range 22-76) with various cardiac and thoracic vascular diseases underwent free-breathing electrocardiogram-gated noncontrast SSFP MRA and conventional high-resolution 3D contrast-enhanced (CE) MRA of the thorax at 1.5 T. Two readers evaluated both datasets for findings: venous visibility and sharpness (from 0, not visualized to 3, excellent definition); artifacts; signal-to-noise ratio (SNR); and contrast-to-noise ratio (CNR) in 8 venous segments including superior vena cava (SVC), supra-diaphragmatic inferior vena cava, bilateral brachiocephalic, proximal subclavian, and lower internal jugular veins. Statistical analysis was performed using Wilcoxon test for overall image quality and vessel visibility, t test for SNR and CNR analysis, and kappa coefficient for inter-observer variability. RESULTS: 3D SSFP and CE-MRA were successfully performed in all patients. Scan time for SSFP MRA ranged from 5 to 10 minutes (mean +/- standard deviation, 7 +/- 2 minutes). Reader 1 (2) graded the overall image quality as excellent and good on SSFP MRA in 23 (25) and 7 (5) patients, and on CE-MRA in 22 (23) and 8 (9) patients, respectively. On SSFP MRA, readers 1 and 2 graded 234 (97.5%) and 233 (97.1%) venous segments with diagnostic definition (grades 2 and 3) (kappa = 0.69), respectively. On conventional CE-MRA, readers 1 and 2 graded 231 (96.3%) and 232 (96.7%) venous segments with diagnostic definition (grades 2 and 3) (kappa = 0.68), respectively. Segmental visibility and sharpness were higher for lower internal jugular veins on CE-MRA for each reader (P < 0.001). No significant difference existed for venous visibility and sharpness scores for other venous segments between the 2 techniques for both readers (P > 0.05). SNR and CNR values were lower for internal jugular veins on SSFP MRA (P < 0.001). No significant difference existed between SNR and CNR values for the other venous segments on SSFP and CE-MRA (P > 0.05 for all). The 2 readers demonstrated patent SVC Glenn shunt to main pulmonary artery (n = 3), patent extra cardiac Fontan shunt from inferior vena cava to pulmonary artery confluence (n = 2), and dilatation and thrombosis of SVC (n = 1) and right brachiocephalic vein (n = 1) on both datasets. CONCLUSION: Free breathing navigator-gated noncontrast 3D SSFP MRA with nonselective radiofrequency excitation provides high image quality and sufficient SNR and CNR for confident evaluation of thoracic central veins.