Noncontrast MR angiography for comprehensive assessment of abdominopelvic arteries using quadruple inversion-recovery preconditioning and 3D balanced steady-state free precession imaging

Purpose:

To develop a noncontrast magnetic resonance angiography (MRA) method for comprehensive evaluation of abdominopelvic arteries in a single 3D acquisition.

Materials and Methods:

A noncontrast MRA (NC MRA) pulse sequence was developed using four inversion‐recovery (IR) pulses and 3D balanced steady‐state free precession (b‐SSFP) readout to provide arterial imaging from renal to external iliac arteries. Respiratory triggered, high spatial resolution (1.3 × 1.3 × 1.7 mm³) noncontrast angiograms were obtained in seven volunteers and ten patients referred for gadolinium‐enhanced MRA (CE MRA). Images were assessed for diagnostic quality by two radiologists. Quantitative measurements of arterial signal contrast were also performed.

Results:

NC MRA imaging was successfully completed in all subjects in 7.0 ± 2.3 minutes. In controls, image quality of NC MRA averaged 2.79 ± 0.39 on a scale of 0–3, where 3 is maximum. Image quality of NC MRA (2.65 ± 0.41) was comparable to that of CE MRA (2.9 ± 0.32) in all patients. Contrast ratio measurements in patients demonstrated that NC MRA provides arterial contrast comparable to source CE MRA images with adequate venous and excellent background tissue suppression.

Conclusion:

The proposed noncontrast MRA pulse sequence provides high‐quality visualization of abdominopelvic arteries within clinically feasible scan times. J. Magn. Reson. Imaging 2011;33:1430–1439. © 2011 Wiley‐Liss, Inc.     

Single breathhold noncontrast thoracic MRA using highly accelerated parallel imaging with a 32-element coil array

Purpose:

To evaluate the feasibility of performing single breathhold three‐dimensional (3D) thoracic noncontrast MR angiography (NC‐MRA) using highly accelerated parallel imaging.

Materials and Methods:

We developed a single breathhold NC MRA pulse sequence using balanced steady state free precession (SSFP) readout and highly accelerated parallel imaging. In 17 subjects, highly accelerated noncontrast MRA was compared against electrocardiogram‐triggered contrast‐enhanced MRA. Anonymized images were randomized for blinded review by two independent readers for image quality, artifact severity in eight defined vessel segments and aortic dimensions in six standard sites. NC‐MRA and CE‐MRA were compared in terms of these measures using paired sample t‐ and Wilcoxon tests.

Results:

The overall image quality (3.21 ± 0.68 for NC‐MRA versus 3.12 ± 0.71 for CE‐MRA) and artifact (2.87 ± 1.01 for NC‐MRA versus 2.92 ± 0.87 for CE‐MRA) scores were not significantly different, but there were significant differences for the great vessel and coronary artery origins. NC‐MRA demonstrated significantly lower aortic diameter measurements compared with CE‐MRA; however, this difference was not considered clinically relevant (>3 mm difference) for less than 12% of segments, most commonly at the sinotubular junction. Mean total scan time was significantly lower for NC‐MRA compared with CE‐MRA (18.2 ± 6.0 s versus 28.1 ± 5.4 s, respectively; P < 0.05).

Conclusion:

Single breathhold NC‐MRA is feasible and can be a useful alternative for evaluation and follow‐up of thoracic aortic diseases. J. Magn. Reson. Imaging 2012;35:963–968. © 2011 Wiley Periodicals, Inc.     

Accelerated noncontrast-enhanced pulmonary vein MRA with distributed compressed sensing

Purpose:

To investigate the efficacy of distributed compressed sensing (CS) to accelerate free‐breathing, electrocardiogram (ECG)‐triggered noncontrast pulmonary vein (PV) magnetic resonance angiography (MRA).

Materials and Methods:

Fully sampled ECG‐triggered noncontrast PV MRA, using a spatially selective slab inversion preparation sequence, was acquired on seven healthy adult subjects (27 ± 17 years, range: 19–65 years, 4 women). The k‐space data were retrospectively randomly undersampled by factors of 2, 4, 6, 8, and 10 and then reconstructed using distributed CS and coil‐by‐coil CS methods. The reconstructed images were evaluated by two blinded readers in consensus for assessment of major PV branches as well as the presence of artifacts in left atrium (LA) and elsewhere. Diameters of right inferior and right superior PV branches were measured. Additionally, mean square errors (MSE) of the reconstructions were calculated.

Results:

Both CS methods resulted in image quality scores similar to the fully sampled reference images at undersampling factors up to 6‐fold for distributed CS and 4‐fold for coil‐by‐coil CS reconstructions. There was no difference in the presence of artifacts in LA and freedom from important artifacts elsewhere between the two techniques up to undersampling factors of 10 compared to the fully sampled reconstruction. For the PV diameters, no systematic variation between the reference and the reconstructions were observed for either technique. There were no significant differences in MSE between the two methods when compared at a given rate, but the difference was significant when compared across all rates.

Conclusion:

The sparsity of noncontrast PV MRA and the joint sparsity of different coil images allow imaging at high undersampling factors (up to 6‐fold) when distributed CS is used. J. Magn. Reson. Imaging 2011;33:1248–1255. © 2011 Wiley‐Liss, Inc.     

Measuring aortic diameter with different MR techniques: Comparison of three‐dimensional (3D) navigated steady‐state free‐precession (SSFP), 3D contrast‐enhanced magnetic resonance angiography (CE‐MRA), 2D T2 black blood,and 2D cine SSFP

Purpose:

To compare nongated three‐dimensional (3D) contrast‐enhanced magnetic resonance angiography (CE‐MRA) with 3D‐navigated cardiac‐gated steady‐state free‐precession bright blood (3D‐nav SSFP) and noncontrast 2D techniques for ascending aorta dimension measurements.

Materials and Methods:

Twenty‐five clinical exams were reviewed to evaluate the ascending aorta at 1.5T using: breathhold cine bright blood (SSFP), cardiac‐triggered T2 black blood (T2 BB), axial 3D‐nav SSFP, and nongated 3D CE‐MRA. Three radiologists independently measured aortic size at three specified locations for each sequence. Means, SDs, interobserver correlation, and vessel edge sharpness were statistically evaluated.

Results:

Measurements were greatest for 3D‐nav SSFP and 3D CE‐MRA and smallest for T2 BB. There was no significant difference between 3D‐nav SSFP and 3D CE‐MRA (P = 0.43–0.86), but significance was observed comparing T2 BB to all sequences. Interobserver agreement was uniformly >0.9, with T2 BB best, followed closely by 3D‐nav SSFP and 2D cine SSFP, and 3D CE‐MRA being the worst. Edge sharpness was significantly poorer for 3D CE‐MRA compared to the other sequences (P < 0.001).

Conclusion:

If diameter measurements are the main clinical concern, 3D‐nav SSFP appears to be the best choice, as it has a sharp edge profile, is easy to acquire and postprocess, and shows very good interobserver correlation. J. Magn. Reson. Imaging 2010;31:177–184. © 2009 Wiley‐Liss, Inc.     

Corticomedullary differentiation of the kidney: Evaluation with noncontrast‐enhanced steady‐state free precession (SSFP) MRI with time‐spatial labeling inversion pulse (time‐SLIP)

Purpose:

To assess whether noncontrast‐enhanced steady‐state free precession (SSFP) magnetic resonance imaging (MRI) with time‐spatial labeling inversion pulse (Time‐SLIP) can improve the visibility of corticomedullary differentiation of the normal kidney.

Materials and Methods:

A series of noncontrast‐enhanced SSFP MRI with Time‐SLIP were performed in 20 patients by using various inversion times (TIs); 500–1800 msec in increments of 100 msec. In‐phase (IP) and opposed‐phase (OP) MR images were also obtained. The signal intensity (SI) of the renal cortex and medulla was measured to calculate corticomedullary contrast ratio (SI of cortex/medulla). Additionally, the visibility of corticomedullary differentiation was visually categorized using a four‐point scale.

Results:

In SSFP with Time‐SLIP, corticomedullary contrast ratio was highest with TI of 1200 msec in eight subjects (40%), followed by 1100 msec in seven (35%) and 1000 msec in three (15%). The corticomedullary contrast ratio in SSFP with optimal Time‐SLIP (4.93 ± 1.25) was significantly higher (P < 0.001) than those of IP (1.46 ± 0.12) and OP (1.43 ± 0.14). The visibility of corticomedullary differentiation was significantly better (P < 0.001) in SSFP images with Time‐SLIP (averaged grade = 4.0) than in IP images (averaged grade = 2.63) and OP images (averaged grade = 2.05).

Conclusion:

SSFP MRI with Time‐SLIP can improve the visibility of renal corticomedullary differentiation without using contrast agents. J. Magn. Reson. Imaging 2012;37:1178–1181. © 2012 Wiley Periodicals, Inc.     

Improved coronary MR angiography using wideband steady state free precession at 3 tesla with sub‐millimeter resolution

Purpose:

To suppress off‐resonance artifacts in coronary artery imaging at 3 Tesla (T), and therefore improve spatial resolution.

Materials and Methods:

Wideband steady state free precession (SSFP) sequences use an oscillating steady state to reduce banding artifacts. Coronary artery images were obtained at 3T using three‐dimensional navigated gradient echo, balanced SSFP, and wideband SSFP sequences.

Results:

The highest in‐plane resolution of left coronary artery images was 0.68 mm in the frequency‐encoding direction. Wideband SSFP produced an average SNR efficiency of 70% relative to conventional balanced SSFP and suppressed off‐resonance artifacts.

Conclusion:

Wideband SSFP was found to be a promising approach for obtaining noncontrast, high‐resolution coronary artery images at 3 Tesla with reliable image quality. J. Magn. Reson. Imaging 2010;31:1224–1229. © 2010 Wiley‐Liss, Inc.     

Impact of partial volume effects on visceral adipose tissue quantification using MRI

Purpose:

To quantitatively estimate the impact of partial volume effects on visceral adipose tissue (VAT) quantification using typical resolution magnetic resonance imaging (MRI).

Materials and Methods:

Nine normal or overweight subjects were scanned at central abdomen levels with a water‐saturated, balanced steady‐state free precession (b‐SSFP) sequence. The water‐saturation effectiveness was evaluated with region‐of‐interest analysis on fat, muscle, bowel, and noise areas. The number of full‐volume (FV) and partial‐volume (PV) fat pixels was estimated based on a gray‐level histogram model of water‐saturated images. Both FV and PV fat amounts were quantified.

Results:

High‐quality, fat‐only images were generated with the b‐SSFP imaging method. Fat SNR was 77.7 ± 25.6 and water‐saturation was effective, with the average fat‐to‐water signal intensity ratio = 20.7 ± 3.8. The average ratio of partial‐ to full‐volume fat amounts was 104.0%. The ratio was higher with lower body mass index (BMI) and PV fat amount only increased slightly when BMI increased.

Conclusion:

PV fat contributes a significant amount of fat to fat measurements on typical spatial resolution MRI on normal and overweight subjects. The relative PV fat contribution is markedly higher in slimmer patients. Inclusion of this portion of the adipose tissue will increase overall accuracy and decrease variability of VAT quantification using MRI. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Comparison of contrast‐enhanced MR angiography to intraarterial digital subtraction angiography for evaluation of peripheral arterial occlusive disease: Results of a phase III multicenter trial

Purpose

To evaluate the efficacy and safety of 0.1 mmol/kg gadodiamide administration for contrast‐enhanced magnetic resonance angiography (CE‐MRA) in detecting hemodynamically relevant main stenosis (ie, ≥50% or occlusion) of aortoiliac arteries.

Materials and Methods

In a multicenter, phase 3, controlled study, patients with suspected or proven peripheral arterial occlusive disease (PAOD) underwent CE‐MRA with administration of gadodiamide. Intraarterial digital subtraction angiography (IA‐DSA) was used as the reference. The study was approved by all Institutional Review Boards or Institutional Ethic Committees prior to commencement of patient recruitment and written informed consent was obtained from all patients.

Results

Independent readers rated 25%–45% of CE‐MRA images as excellent compared with 0.3%–6% of noncontrast MRA images. Mean imaging acquisition time for CE‐MRA was <1 minute (0.7 ± 1.9 minutes) versus 10 minutes (10.8 ± 3.0) for noncontrast MRA. Sensitivity, specificity, and accuracy of CE‐MRA were superior compared with those of noncontrast MRA in detecting significant arterial stenoses. Compared with IA‐DSA, the sensitivity of CE‐MRA ranged from 80%–88% and the specificity from 73% to 92% for the three blinded readers, at the patient level.

Conclusion

Diagnostic results with CE‐MRA were superior and more consistent compared with noncontrast MRA for detecting hemodynamically relevant main stenoses in patients with suspected or proven PAOD and compared favorably with IA‐DSA as a reference standard. J. Magn. Reson. Imaging 2010;31:1402–1410. © 2010 Wiley‐Liss, Inc.     

Volume‐targeted and whole‐heart coronary magnetic resonance angiography using an intravascular contrast agent

Purpose

To compare volume‐targeted and whole‐heart coronary magnetic resonance angiography (MRA) after the administration of an intravascular contrast agent.

Materials and Methods

Six healthy adult subjects underwent a navigator‐gated and ‐corrected (NAV) free breathing volume‐targeted cardiac‐triggered inversion recovery (IR) 3D steady‐state free precession (SSFP) coronary MRA sequence (t‐CMRA) (spatial resolution = 1 × 1 × 3 mm³) and high spatial resolution IR 3D SSFP whole‐heart coronary MRA (WH‐CMRA) (spatial resolution = 1 × 1 × 2 mm³) after the administration of an intravascular contrast agent B‐22956. Subjective and objective image quality parameters including maximal visible vessel length, vessel sharpness, and visibility of coronary side branches were evaluated for both t‐CMRA and WH‐CMRA.

Results

No significant differences (P = NS) in image quality were observed between contrast‐enhanced t‐CMRA and WH‐CMRA. However, using an intravascular contrast agent, significantly longer vessel segments were measured on WH‐CMRA vs. t‐CMRA (right coronary artery [RCA] 13.5 ± 0.7 cm vs. 12.5 ± 0.2 cm; P < 0.05; and left circumflex coronary artery [LCX] 11.9 ± 2.2 cm vs. 6.9 ± 2.4 cm; P < 0.05). Significantly more side branches (13.3 ± 1.2 vs. 8.7 ± 1.2; P < 0.05) were visible for the left anterior descending coronary artery (LAD) on WH‐CMRA vs. t‐CMRA. Scanning time and navigator efficiency were similar for both techniques (t‐CMRA: 6.05 min; 49% vs. WH‐CMRA: 5.51 min; 54%, both P = NS).

Conclusion

Both WH‐CMRA and t‐CMRA using SSFP are useful techniques for coronary MRA after the injection of an intravascular blood‐pool agent. However, the vessel conspicuity for high spatial resolution WH‐CMRA is not inferior to t‐CMRA, while visible vessel length and the number of visible smaller‐diameter vessels and side‐branches are improved. J. Magn. Reson. Imaging 2009;30:1191–1196. © 2009 Wiley‐Liss, Inc.     

Whole‐heart coronary magnetic resonance angiography at 3.0T using short‐TR steady‐state free precession,vastly undersampled isotropic projection reconstruction

Purpose

To evaluate the feasibility of improving 3.0T steady‐state free precession (SSFP) whole‐heart coronary magnetic resonance angiography (MRA) using short‐TR (repetition time) VIPR (vastly undersampled isotropic projection reconstruction).

Materials and Methods

SSFP is highly sensitive to field inhomogeneity. VIPR imaging uses nonselective radiofrequency pulses, allowing short TR and reduced banding artifacts, while achieving isotropic 3D resolution. Coronary artery imaging was performed in nine healthy volunteers using SSFP VIPR. TR was reduced to 3.0 msec with an isotropic spatial resolution of 1.3 × 1.3 × 1.3 mm³. Image quality, vessel sharpness, and lengths of major coronary arteries were measured. Comparison between SSFP using Cartesian trajectory and SSFP using VIPR trajectory was performed in all volunteers.

Results

Short‐TR SSFP VIPR resulted in whole‐heart images without any banding artifacts, leading to excellent coronary artery visualization. The average image quality score for VIPR‐SSFP was 3.12 ± 0.42 out of four while that for Cartesian SSFP was 0.92 ± 0.61. A significant improvement (P < 0.05) in image quality was shown by Wilcoxon comparison. The visualized coronary artery lengths for VIPR‐SSFP were: 10.13 ± 0.79 cm for the left anterior descending artery (LAD), 7.90 ± 0.91 cm for the left circumflex artery (LCX), 7.50 ± 1.65 cm for the right coronary artery (RCA), and 1.84 ± 0.23 cm for the left main artery (LM). The lengths statistics for Cartesian SSFP were 1.57 ± 2.02 cm, 1.54 ± 1.93 cm, 0.94 ± 1.17 cm, 0.46 ± 0.53 cm, respectively. The image sharpness was also increased from 0.61 ± 0.13 (mm^?1) in Cartesian‐SSFP to 0.81 ± 0.11 (mm^?1) in VIPR‐SSFP.

Conclusion

With VIPR trajectory the TR is substantially decreased, reducing the sensitivity of SSFP to field inhomogeneity and resulting in whole‐heart images without banding artifacts at 3.0T. Image quality improved significantly over Cartesian sampling. J. Magn. Reson. Imaging 2010; 31:1230–1235. © 2010 Wiley‐Liss, Inc.

     

3D noncontrast MR angiography of the distal lower extremities using flow‐sensitive dephasing (FSD)‐prepared balanced SSFP

While three‐dimensional contrast‐enhanced MR angiography (MRA) is becoming the method of choice for clinical peripheral arterial disease (PAD) examinations, safety concerns with contrast administration in patients with renal insufficiency have triggered a renaissance of noncontrast MRA. In this work, a noncontrast‐MRA technique using electrocardiography‐triggered three‐dimensional segmented balanced steady‐state free precession with flow‐sensitive dephasing (FSD) magnetization preparation was developed and tested in the distal lower extremities. FSD preparation was used to induce arterial flow voids at systolic cardiac phase while having little effect on venous blood and static tissues. High‐spatial‐resolution MRA was obtained by means of magnitude subtraction between a dark‐artery scan with FSD preparation at systole and a bright‐artery scan without FSD preparation at mid‐diastole. In nine healthy volunteers, FSD parameters, including the gradient waveform and the first‐order gradient moment, were optimized for excellent MRA image quality. Furthermore, arterial stenosis and occlusion in two peripheral arterial disease patients were identified using the noncontrast‐MRA technique, as confirmed by contrast‐enhanced MRA. In conclusion, FSD‐prepared balanced steady‐state free precession in conjunction with electrocardiography gating and image subtraction provides a promising noncontrast‐MRA strategy for the distal lower extremities. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Time‐resolved three‐dimensional magnetic resonance digital subtraction angiography without contrast material in the brain: Initial investigation

Purpose

To evaluate a novel magnetic resonance (MR) angiography (MRA) of three‐dimensional (3D) MR digital subtraction angiography (MRDSA) without contrast material, which is essentially 3D true steady‐state free precession (SSFP) with selected inversion recovery (IR) pulse using multiple cardiac phase acquisitions with a short increment delay in the assessment of normal cranial arteries, as a feasibility study before clinical use.

Materials and Methods

Serial MRA images using 3D MRDSA without contrast material were acquired from 10 healthy volunteers. Visualization of normal cranial arteries with time‐spatial labeling inversion pulse (Time‐SLIP) MRDSA was qualitatively compared with the conventional MRA method, 3D time‐of‐flight (TOF)‐MRA.

Results

In all volunteers, serial 3D MRDSAs containing hemodynamic information were successfully imaged. The results of visualization of the branches of the cranial arteries with Time‐SLIP MRDSA were comparable to those of 3D TOF‐MRA. The mean scores ± standard deviations for normal cerebral arteries (internal carotid arteries, middle cerebral arteries, anterior cerebral arteries, posterior cerebral arteries, and basilar arteries) were 2.4 ± 0.5, 2.3 ± 0.5, 2.0 ± 0.7, 2.3 ± 0.7, and 2.5 ± 0.7, respectively.

Conclusion

Time‐SLIP 3D MRDSA is a simple method for obtaining hemodynamic information. Although more MR sequence improvement is needed, it can play an important role in assessing cranial arteries without contrast material. J. Magn. Reson. Imaging 2009;30:214–218. © 2009 Wiley‐Liss, Inc.     

Nonenhanced ECG-gated time-resolved 4D Steady-state free precession (SSFP) MR angiography (MRA) for assessment of cerebral collateral flow: comparison with digital subtraction angiography (DSA)

Objectives

To evaluate a nonenhanced time-resolved 4D SSFP MRA for dynamic visualization of intracranial collateral blood flow.

Methods

22 patients (59.0?±?11.8 years) with steno-occlusive disease of brain-supplying arteries were included in this study. 4D SSFP MRA of the intracranial arteries was acquired with 15 temporal phases and a temporal resolution of 115 ms using 1.5 T MR. Cerebral DSA served as the reference standard and was available in all patients.

Results

Nonenhanced 4D SSFP MRA allowed for detailed dynamic visualization of blood flow in the circle of Willis and its branches in 21 of 22 (95.5%) patients. Collateral flow was excluded with both 4D SSFP MRA and DSA in 4 patients. In 17 patients, DSA detected anterior collateral flow (n?=?8), posterior collateral flow via the right (n?=?8) and left (n?=?7) posterior communicating artery as well as patent EC-IC bypasses (n?=?8). 29 of 31 collateral flow pathways were visualized by 4D SSFP MRA. As compared to DSA, 4D SSFP MRA showed a high sensitivity (92.3%), specificity (100%), positive predictive value (100%) and negative predictive value (95.2%) for visualization of intracranial collateral flow.

Conclusions

4D SSFP MRA is a promising non-invasive imaging technique for dynamic visualization of intracranial collateral flow.     

Time-resolved magnetic resonance angiography: evaluation of intrapulmonary circulation parameters in pulmonary arterial hypertension

Purpose

To determine whether pulmonary arterial and venous transit times measured by time‐resolved magnetic resonance angiography (MRA) can be used as a diagnostic tool for pulmonary arterial hypertension (PAH).

Materials and Methods

Twelve patients with confirmed PAH and 10 healthy volunteers were scanned with Institutional Review Board (IRB) approval. Time‐resolved MRA and 2D phase contrast flow images of the pulmonary vasculature were acquired. Pulmonary arterial and venous transit times (PaTT and PvTT) and pulmonary valve flow (PVF) were obtained. Pulmonary arterial and pulmonary venous blood volumes (PaBV and PvBV) were calculated as the product of flow and transit time.

Results

Patients with PAH showed statistically significant increases in PaTT and PvTT (P < 0.0004, P < 0.05, respectively) compared to controls. PaBV (165.2 ± 92.0 mL) was significantly higher in PAH subjects than controls (97.0 ± 47.1 mL) (P < 0.04), whereas PvBV (127.9 ± 148.9 mL) of PAH subjects had no significant increase from those of healthy controls (142.5 ± 104.1 mL) (P < 0.38).

Conclusion

Pulmonary arterial transit times measured using time‐resolved MRA can be used as a simple, noninvasive metric for detection of altered hemodynamics in PAH. J. Magn. Reson. Imaging 2011;33:225–231. © 2010 Wiley‐Liss, Inc.     

Precision of pulmonary vein diameter measurements assessed by CE-MRA and steady-state-free precession imaging

Objective

Pulmonary vein (PV) diameter assessment is important for planning and follow-up of PV ablation in atrial fibrillation. Therefore, the aim of our study was to evaluate inter- and intraobserver reliability of PV diameter measurements by contrast-enhanced magnetic resonance angiography (CE-MRA) and ECG-gated 2D multislice unenhanced steady-state-free precession sequences (multislice SSFP).

Methods

Sixty PV diameters in 17 consecutive patients were measured in transverse and coronal orientation with CE-MRA and multislice SSFP by two observers. Statistics to evaluate inter- and intraobserver reliability included Bland-Altman analysis and F-test.

Results

Intraobserver limits of agreement (LAG) ranged between ±0.50 cm (transverse) and ±0.86 cm (coronal) for CE-MRA versus ±0.40 cm (transverse) and ±0.67 cm (coronal) for multislice SSFP. Interobserver agreement showed LAG ranging between ±0.59 cm (transverse) and ±0.83 cm (coronal) for CE-MRA versus ±0.34 cm (transverse) and ±0.75 cm (coronal) for multislice SSFP. Intra- and interobserver variances did not reveal significant differences between CE-MRA and multislice SSFP in any orientation (all p-values >0.05).

Conclusion

Multislice SSFP and CE-MRA enable comparable precision of PV diameter measurements. However, both methods reveal a wide range of intra- and interobserver agreement, which has to be thoroughly considered in clinical use.

Key Points

? Unenhanced magnetic resonance imaging can now provide measurement of pulmonary vein diameters ? Steady-state-free precession offers a new method of performing unenhanced MR imaging ? Both unenhanced and enhanced MRI measurements show wide intra- and interobserver variation ? PV diameter measurements assessed by MRI have to be interpreted with care ? Nevertheless, unenhanced MRI might replace some CT examinations for pulmonary vein demonstration     

Arterial flow characteristics in the presence of vascular disease and implications for fast spin echo-based noncontrast MR angiography

Purpose:

To investigate arterial flow characteristics in the setting of vascular disease, and examine their effect on the performance of fast spin‐echo (FSE)‐based noncontrast MR angiography (NC‐MRA).

Materials and Methods:

Seventeen patients were recruited from among those scheduled for routine contrast‐enhanced MR angiography (CE‐MRA) of the lower extremities at 1.5 Tesla. The research portion of the exam was performed before the clinically‐indicated protocol and included phase‐contrast imaging at multiple levels in the legs and FSE‐based NC‐MRA in the calf and thigh, using a three‐dimensional ECG‐gated technique that exploits differences in arterial flow velocity between diastole and systole.

Results:

Vascular occlusions were associated with reduced systolic velocity, a delayed systolic peak, and, in two middle‐aged patients, an increase in diastolic velocity. Elevated systolic and diastolic velocities were observed in a subject with a nonhealing ulcer. NC‐MRA allowed visualization of arteries with systolic velocities as low as 3 cm/s, and exhibited comparable depiction to CE‐MRA for diastolic velocities as high as 6 cm/s. At the highest diastolic velocities observed (15 cm/s) arterial depiction was severely degraded.

Conclusion:

FSE‐based NC‐MRA as presently implemented performs successfully over a wide range of flow patterns, but does not accommodate extremely low systolic velocities or very high diastolic velocities. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Neonatal cardiac MRI using prolonged balanced SSFP imaging at 3T with active frequency stabilization

Cardiac MRI in neonates holds promise as a tool that can provide detailed functional information in this vulnerable group. However, their small size, rapid heart rate, and inability to breath‐hold, pose particular challenges that require prolonged high‐contrast and high‐SNR methods. Balanced‐steady state free precession (SSFP) offers high SNR efficiency and excellent contrast, but is vulnerable to off‐resonance effects that cause banding artifacts. This is particularly problematic in the blood‐pool, where off‐resonance flow artifacts severely degrade image quality. Methods: In this article, we explore active frequency stabilization, combined with image‐based shimming, to achieve prolonged SSFP imaging free of banding artifacts. The method was tested using 2D multislice SSFP cine acquisitions on 18 preterm infants, and the functional measures derived were validated against phase‐contrast flow assessment. Results: Significant drifts in the resonant frequency (165 ± 23Hz) were observed during 10‐min SSFP examinations. However, full short‐axis stacks free of banding artifacts were achieved in 16 subjects with stabilization; the cardiac output obtained revealed a mean difference of 9.0 ± 8.5% compared to phase‐contrast flow measurements. Conclusion: Active frequency stabilization has enabled the use of prolonged SSFP acquisitions for neonatal cardiac imaging at 3T. The findings presented could have broader implications for other applications using prolong SSFP acquisitions. Magn Reson Med 70:776–784, 2013. © 2012 Wiley Periodicals, Inc.     

Effective motion-sensitizing magnetization preparation for black blood magnetic resonance imaging of the heart

Purpose

To investigate the effectiveness of flow signal suppression of a motion‐sensitizing magnetization preparation (MSPREP) sequence and to optimize a 2D MSPREP steady‐state free precession (SSFP) sequence for black blood imaging of the heart.

Materials and Methods

Using a flow phantom, the effect of varying field of speed (FOS), b‐value, voxel size, and flow pattern on the flow suppression was investigated. In seven healthy volunteers, black blood images of the heart were obtained at 1.5T with MSPREP‐SSFP and double inversion recovery fast spin echo (DIR‐FSE) techniques. Myocardium and blood signal‐to‐noise ratio (SNR) and myocardium‐to‐blood contrast‐to‐noise ratio (CNR) were measured. The optimal FOS that maximized the CNR for MSPREP‐SSFP was determined.

Results

Phantom data demonstrated that the flow suppression was induced primarily by the velocity encoding effect. In humans, FOS = 10–20 cm/s was found to maximize the CNR for short‐axis (SA) and four‐chamber (4C) views. Compared to DIR‐FSE, MSPREP‐SSFP provided similar blood SNR efficiency in the SA basal and mid‐views and significantly lower blood SNR efficiency in the SA apical (P = 0.02) and 4C (P = 0.01) views, indicating similar or better blood suppression.

Conclusion

Velocity encoding is the primary flow suppression mechanism of the MSPREP sequence and 2D MSPREP‐SSFP black blood imaging of the heart is feasible in healthy subjects. J. Magn. Reson. Imaging 2008;28:1092–1100. © 2008 Wiley‐Liss, Inc.     

Ultrashort echo time MR imaging with off‐resonance saturation for characterization of pathologically altered Achilles tendons at 3 T

Off‐resonance radiofrequency saturation pulses applied prior to regular excitation in MR sequences can be used to modify signal contrast based on magnetization transfer and direct saturation effects. Clinical applicability and value of ultrashort echo time sequences combined with off‐resonance saturation pulses was tested in 16 healthy and 14 tendinopathic as well as paratendinopathic Achilles tendons in vivo at 3 T. A 3D ultrashort echo time sequence in combination with a gaussian off‐resonance saturation pulse (frequency offset: 1000–5000 Hz) was used to modify the detectable MR signal intensity from the Achilles tendon. Off‐resonance saturation ratio was calculated as the relative reduction in signal intensity under selective off‐resonance saturation in relation to a reference measurement without any saturation pulse. Off‐resonance saturation ratio in tendons of healthy volunteers ranged from 0.52 ± 0.06 (1000 Hz) to 0.24 ± 0.02 (5000 Hz), whereas symptomatic tendinopathic tendons (0.35 ± 0.04 to 0.17 ± 0.02) and asymptomatic tendinopathic tendons (0.41 ± 0.06 to 0.21 ± 0.02) showed significantly lower mean off‐resonance saturation ratio values. Off‐resonance saturation ratio values might provide a sensitive and quantitative marker for assessment of pathological microstructure alterations of the Achilles tendon. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

MR angiography of the cerebral perforating arteries with magnetization prepared anatomical reference at 7T: Comparison with time‐of‐flight

Purpose

To develop a magnetic resonance imaging (MRI) protocol that visualizes both the perforating arteries and the related anatomy in a single acquisition at 7T.

Material and Methods

T₁‐weighted magnetization prepared imaging (MPRAGE) was empirically modified for use as angiography method at 7T. The resulting sequence depicts the vasculature simultaneously with the surrounding anatomical structures, and is referred to as “magnetization prepared anatomical reference MRA” (MPARE‐MRA). The method was compared to time‐of‐flight (TOF) MRA in seven healthy subjects. The conspicuity of the perforating arteries and the contrast between gray and white matter were evaluated both quantitatively by contrast‐to‐noise (CNR) measurements, and qualitatively by two radiologists who scored the images.

Results

The contrast‐to‐noise ratio (CNR) between blood and background was 28 ± 9 for MPARE‐MRA and 35 ± 16 for TOF‐MRA, indicating good conspicuity of the vessels. CNR values were: internal capsule (IC) vs. caudate head (CH): 4.2 ± 0.7; IC vs. putamen: 3.5 ± 0.6; white matter vs. gray matter: 9.7 ± 2.5.

Conclusion

The benefits of ultra‐high‐field MRI can transform MPRAGE into a new angiography method to image small vessels and associated parenchyma at the same time. This technique can be used to study the correlation between tissue damage and vascular pathology. J. Magn. Reson. Imaging 2008;28:1519–1526. © 2008 Wiley‐Liss, Inc.