3D TOF MRA of intracranial aneurysms at 1.5 T and 3 T: influence of matrix, parallel imaging, and acquisition time on image quality - a vascular phantom study

RATIONALE AND OBJECTIVES: A 3-T magnetic resonance imaging system provides a better signal-to-noise ratio and inflow effect than 1.5 T in three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA). The purpose of this study is to analyze the influence of matrix, parallel imaging, and acquisition time on image quality of 3D TOF MRA at 1.5 and 3 T, and to illustrate whether the combination of larger matrixes with parallel imaging technique is feasible, by evaluating the visualization of simulated intracranial aneurysms and aneurysmal blebs using a vascular phantom with pulsatile flow. MATERIALS AND METHODS: An anthropomorphic vascular phantom was designed to simulate the various intracranial aneurysms with aneurysmal bleb. The vascular phantom was connected to an electromagnetic flow pump with pulsatile flow, and we obtained 1.5- and 3-T MRAs altering the parameters of 3D TOF sequences, including acquisition time. Two radiologists evaluated the depiction of simulated aneurysms and aneurysmal blebs. RESULTS: The aneurysmal blebs were not sufficiently visualized on the high-spatial resolution 1.5-T MRA (matrix size of 384 x 256 or 512 x 256), even with longer acquisition time (9 or 18 min). At 3 T with acquisition time of 4.5 min using parallel imaging technique, however, the depiction of aneurysmal blebs was significantly better for the high-spatial resolution sequence than for the standard resolution sequence. For the high-spatial resolution sequence, the longer acquisition times did not improve the depiction of aneurysmal blebs in comparison with 4.5 min at 3 T. CONCLUSIONS: For 3D TOF MRA, the combination of the large matrix with parallel imaging technique is feasible at 3 T, but not at 1.5 T.     

Three-dimensional breathhold SSFP coronary MRA: a comparison between 1.5T and 3.0T

PURPOSE: To assess the feasibility of three-dimensional breathhold coronary magnetic resonance angiography (MRA) at 3.0T using the steady-state free precession (SSFP) sequence, and quantify the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) gains of coronary MRA from 1.5T to 3.0T using whole-body and phased-array cardiac coils as the signal receiver. MATERIALS AND METHODS: Eight healthy volunteers were scanned on 1.5T and 3.0T whole-body systems using the SSFP sequence. Numerical simulations were performed for the SSFP sequence to optimize the flip angle and predict signal enhancement from 1.5T to 3.0T. Coronary artery images were acquired with the whole-body coil in transmit-receive mode or transmit-only with phased-array cardiac coil receivers. RESULTS: In vivo studies of the same volunteer group at both field strengths showed increases of 87% in SNR and 83% in CNR from 1.5T to 3.0T using a whole-body coil as the signal receiver. The corresponding increases using phased-array receivers were 53% in SNR and 92% in CNR. However, image quality at 3.0T was more variable than 1.5T, with increased susceptibility artifacts and local brightening as the result of increased B(0) and B(1) inhomogeneities. CONCLUSION: Coronary MRA at 3.0T using a three-dimensional breathhold SSFP sequence is feasible. Improved SNR at 3.0T warrants the use of coronary MRA with faster acquisition and/or improved spatial resolution. Further investigations are required to improve the consistency of image quality and signal uniformity at 3.0T.     

Comparison of fast spiral,echo planar,and fast low-angle shot MRI for cardiac volumetry at .5T

The application of fast imaging is necessary to reduce the scanning time for cardiac volumetric MRI. Fast spiral, echo planar imaging (EPI), and fast low-angle shot (FLASH) imaging are rapid MRI techniques that allow image acquisition within a fraction of a second. Performed as a multi-shot technique, breath-hold imaging with high temporal and spatial resolution is feasible. This study evaluated the accuracy of interleaved spiral, EPI, and FLASH imaging for measuring ventricular volume and mass at .5T. Breath-hold short-axis cines in parallel planes covering both ventricles were acquired in 16 volunteers with all three fast methods, as well as with conventional gradient-echo imaging for comparison. All fast techniques showed good agreement with conventional imaging. Despite its lower temporal resolution, FLASH imaging yielded higher image quality than EPI and spiral, making FLASH more reliable and suggesting that at .5T, it is the method of choice for rapid cardiac volumetric imaging.     

Comparison of inversion recovery asymmetrical spin-echo EPI and gradient-echo EPI for brain motor activation study

An inversion recovery asymmetric spin-echo (IR-ASE) echo-planar imaging (EPI) sequence has been developed for functional studies of the brain. This technique uses an 180° inversion pulse with a long inversion time (TI) to suppress the pulsatile cerebrospinal fluid and an asymmetric spin-echo readout to obtain activation signals from brain capillaries. Because gradient-echo sequences are most sensitive to large vessels, motor cortex activation studies using a gradient-echo technique also were conducted for comparison with the IR-ASE method. The results suggest that the IR-ASE pulse sequence may be a useful complement to the gradient-echo technique for the study of neuronal activity of the human brain.     

高场强磁共振EPI-FE-T2WI序列在脑出血性病变的应用价值

目的 探讨EPI-FE-BWI序列对脑出血性病变的应用价值。方法使用1．5T磁共振仪对2002年10月至2004年11月2a内2242例进行头部常规序列加做EPI-FE-BWI序列扫描，共发现脑内出血性病变377例。结果在425例脑内出血性病变患者中，脑内血肿155例，微小脑内出血灶131例，肿瘤内出血37例，脑梗死灶内出血43例，蛛网膜下腔出血19例，放射性脑病合并出血4例，血管畸形18例，红斑狼疮性脑损害并出血1例，手术后出血12例，以及外伤性脑出血5例。结论EPI-FE-T2WI序列是检测各种脑内出血性病变的最佳序列。该序列可以用作头部扫描的常规序列，对于脑内出血性疾病的诊断、鉴别诊断及分期有重要的价值。     

Heartbeat-related distension and displacement of the thoracic aorta in healthy volunteers

Purpose

To test our hypothesis that distension and displacement in various segments of the healthy thoracic aorta are significant and can be predicted based on clinical characteristics.

Materials and methods

Sixty-one Caucasian volunteers without cardiovascular disease (49 ± 16 years, range 19–82; 28 men, 33 women) divided into two age groups (A: <50, B: ≥50 years) underwent 1.5-T MRI. ECG-gated dynamic data sets were acquired at five locations perpendicular to the thoracic aorta. Aortic distension and Centre of Mass (CoM) displacement were determined as percentages of diastolic aortic diameter. A multiple linear regression model including age group, gender, location, mean arterial blood pressure, heart rate and body mass index was tested.

Results

Mean aortic distension averaged over all locations was 11.2 ± 4.1% (age group A) and 6.7 ± 3.3% (age group B), mean displacement 15.1 ± 8.3% (A) and 11.0 ± 6.2% (B). Systolic and diastolic aortic diameter and CoM position significantly differed at all locations (p < 0.001). Distension and displacement could be predicted based on the regression model (p < 0.001). Age group A and women exhibited significantly greater distension and displacement compared to age group B (p < 0.001) and men (p < 0.01), respectively. Distension increased, displacement decreased from proximal to distal.

Conclusion

Distension and translational displacement are significant at all levels of the thoracic aorta and can be predicted based on clinical characteristics.     

Segmentation of carotid plaque using multicontrast 3D gradient echo MRI

Purpose:

To evaluate the performance of automatic segmentation of atherosclerotic plaque components using solely multicontrast 3D gradient echo (GRE) magnetic resonance imaging (MRI).

Materials and Methods:

A total of 15 patients with a history of recent transient ischemic attacks or stroke underwent carotid vessel wall imaging bilaterally with a combination of 2D turbo spin echo (TSE) sequences and 3D GRE sequences. The TSE sequences included T1‐weighted, T2‐weighted, and contrast‐enhanced T1‐weighted scans. The 3D GRE sequences included time‐of‐flight (TOF), magnetization‐prepared rapid gradient echo (MP‐RAGE), and motion‐sensitized driven equilibrium prepared rapid gradient echo (MERGE) scans. From these images, the previously developed morphology‐enhanced probabilistic plaque segmentation (MEPPS) algorithm was retrained based solely on the 3D GRE sequences to segment necrotic core (NC), calcification (CA), and loose matrix (LM). Segmentation performance was assessed using a leave‐one‐out cross‐validation approach via comparing the new 3D‐MEPPS algorithm to the original MEPPS algorithm that was based on the traditional multicontrast protocol including 2D TSE and TOF sequences.

Results:

Twenty arteries of 15 subjects were found to exhibit significant plaques within the coverage of all imaging sequences. For these arteries, between new and original MEPPS algorithms, the areas per slice exhibited correlation coefficients of 0.86 for NC, 0.99 for CA, and 0.80 for LM; no significant area bias was observed.

Conclusion:

The combination of 3D imaging sequences (TOF, MP‐RAGE, and MERGE) can provide sufficient contrast to distinguish NC, CA, and LM. Automatic segmentation using 3D sequences and traditional multicontrast protocol produced highly similar results. J. Magn. Reson. Imaging 2012;35:812–819. © 2011 Wiley Periodicals, Inc.     

Nonenhanced ECG-gated time-resolved 4D steady-state free precession (SSFP) MR angiography (MRA) of cerebral arteries: comparison at 1.5T and 3T

Purpose

To compare image quality of nonenhanced time-resolved 4D steady-state free precession MR angiography (4D SSFP MRA) of cerebral arteries at 1.5 T and 3 T.

Materials and methods

12 healthy subjects (mean age 29.4 ± 6.9 years) were studied at both 1.5 T and 3 T. Two different positions of the acquisition slab were evaluated; in one acquisition the imaging slab included the carotid siphon (“S_low”), in the other acquisition the imaging slab was placed superior to the carotid siphon (“S_high”). Subjective image quality of cerebral arteries was assessed independently by two readers on a 4-point scale. Relative Signal-to-Noise-Ratio (SNR) was determined for the M1 segment of the middle cerebral artery.

Results

Subjective image quality of the anterior cerebral artery (segments A1, A2) was significantly higher at 1.5 T as compared to 3 T, while 3 T provided significantly higher image quality for segment P3 of the posterior cerebral artery. For the middle cerebral artery (segments M1–M3), image quality was significantly higher at 1.5 T than at 3 T when the carotid siphon was included in the acquisition slab (“S_low”), while no significant difference was found between 1.5 T and 3 T with “S_high”. Relative SNR was significantly higher at 1.5 T (23.1 ± 5.1) as compared to 3 T (12.1 ± 7.8) for “S_low” and significantly higher at 3 T (29.8 ± 5.9) than at 1.5 T (24.2 ± 3.6) for “S_high”.

Conclusion

Our results indicate that 4D SSFP MRA should preferably be performed at 1.5 T with inclusion of the carotid siphon in the acquisition slab, which might be required for the assessment of intracranial collateral flow.     

3T MRI腰骶部脊神经根扩散张量成像在腰椎间盘突出症中的应用价值

目的 探索扩散张量成像(diffusion tensor imaging,DTI)和纤维示踪成像(fibre tracking,FT)显示腰骶脊神经根的可行性,并评估椎间盘突出症患者L4及L5脊神经根各向异性分数(fractional anisotropy,FA)和表观扩散系数(apparent diffusion coefficient,ADC)值的差别.方法 20例由于后外侧或椎间孔椎间盘突出引起单侧坐骨神经痛的患者和20例健康志愿者纳入研究.所有检查均在Philips Achieve 3.0 T TX MRI上进行,纤维示踪成像参数:FA阈值＝0.15;最小纤维束长度=10mm;最大角度=27°.应用横轴位T2解剖融合图像序列评估重建图像的相关性.对所有被检者的L4、L5和S1脊神经根行扩散张量和纤维示踪成像,并在FA图和ADC图上测量L4和L5脊神经根的平均FA值和ADC值.结果 腰椎间盘突出症患者和健康志愿者腰骶部脊神经根纤维束成像在T2解剖融合图像上完全匹配.在纤维示踪图像上可以清晰地辨别腰骶部脊神经根受压位置.所有患者和健康志愿者的FA值和ADC值可以从FA图和ADC图上获得.受压侧脊神经根的FA值显著低于对侧神经根(P＜0.01)和健康志愿者的(P＜0.01); ADC值显著高于对侧神经根(P＜0.01)和健康志愿者的(P＜0.01).结论 3T MRI腰骶部脊神经根扩散张量和纤维示踪成像是可行的.腰椎间盘突出症患者受压L4和L5脊神经根的FA值和ADC值有显著性的变化.     

Dual half‐echo phase correction for implementation of 3D radial SSFP at 3.0 T

Fat/water separation methods such as fluctuating equilibrium magnetic resonance and linear combination steady‐state free precession have not yet been successfully implemented at 3.0 T due to extreme limitations on the time available for spatial encoding with the increase in magnetic field strength. We present a method to utilize a three‐dimensional radial sequence combined with linear combination steady‐state free precession at 3.0 T to take advantage of the increased signal levels over 1.5 T and demonstrate high spatial resolution compared to Cartesian techniques. We exploit information from the two half‐echoes within each pulse repetition time to correct the accumulated phase on a point‐by‐point basis, thereby fully aligning the phase of both half‐echoes. The correction provides reduced sensitivity to static field (B₀) inhomogeneity and robust fat/water separation. Resultant images in the knee joint demonstrate the necessity of such a correction, as well as the increased isotropic spatial resolution attainable at 3.0 T. Results of a clinical study comparing this sequence to conventional joint imaging sequences are included. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Artifacts in 3-T MRI: physical background and reduction strategies

Magnetic resonance imaging (MRI) at a field-strength of 3 T has become more and more frequently used in recent years. In an increasing number of radiological sites, 3-T MRI now starts to play the same role for clinical imaging that was occupied by 1.5-T systems in the past. Because of physical limitations related to the higher field strength and because of protocols transferred from 1.5-T MRI that are not yet fully optimized for 3 T, radiologists and technicians working at these systems are relatively often confronted with image artifacts related to 3-T MRI. The purpose of this review article is to present the most relevant artifacts that arise in 3-T MRI, to provide some physical background on the formation of artifacts, and to suggest strategies to reduce or avoid these artifacts. The discussed artifacts are classified and ordered according to the physical mechanism or property of the MRI system responsible for their occurrence: artifacts caused by B0 inhomogeneity and susceptibility effects, B1 inhomogeneity and wavelength effects, chemical-shift effects, blood flow and magnetohydrodynamics, and artifacts related to SNR.     

Comparison of spiral imaging and SENSE‐EPI at 1.5 and 3.0 T using a controlled cerebrovascular challenge

Purpose

To quantitatively compare spiral imaging and sensitivity‐encoded‐echo‐planar‐imaging (SENSE‐EPI) methods for blood oxygen level‐dependent (BOLD) imaging using controlled changes in the end‐tidal partial pressure of CO₂ (PetCO₂) to provide a global BOLD response. Specifically, we examined susceptibility‐field‐gradient effects on the BOLD sensitivity throughout the brain.

Materials and Methods

We quantified cerebrovascular reactivity (CVR) using the BOLD response to cyclic changes in PetCO₂ in five healthy volunteers at 1.5 and 3.0 T using spiral imaging and SENSE‐EPI. We compared the two techniques with respect to susceptibility‐induced signal dropout and CVR t‐statistic.

Results

Compared to spiral imaging, SENSE‐EPI significantly reduced the volume of signal dropout by 32 ± 18% at 3.0 T. In regions with large susceptibility gradients, SENSE‐EPI demonstrated a trend for a greater t‐statistic than spiral imaging, particularly at 3.0 T. However, no statistically significant between‐technique differences existed.

Conclusion

The results at 3.0 T suggest that, compared with spiral imaging, SENSE‐EPI reduces signal loss associated with susceptibility field gradients in affected regions without affecting BOLD sensitivity. This study also demonstrates a unique application of controlled PetCO₂ changes to quantitatively compare BOLD techniques, which may be useful for the design of future fMRI studies. J. Magn. Reson. Imaging 2009;29:1206–1210. © 2009 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.     

Three-dimensional gradient echo versus spin echo sequence in contrast-enhanced imaging of the pituitary gland at 3 T

Introduction

To clarify whether a three-dimensional-gradient echo (3D-GRE) or spin echo (SE) sequence is more useful for evaluating sellar lesions on contrast-enhanced T1-weighted MR imaging at 3.0 Tesla (T).

Methods

We retrospectively assessed contrast-enhanced T1-weighted images using 3D-GRE and SE sequences at 3.0 T obtained from 33 consecutive patients with clinically suspected sellar lesions. Two experienced neuroradiologists evaluated the images qualitatively in terms of the following criteria: boundary edge of the cavernous sinus and pituitary gland, border of sellar lesions, delineation of the optic nerve and cranial nerves within the cavernous sinus, susceptibility and flow artifacts, and overall image quality.

Results

At 3.0 T, 3D-GRE provided significantly better images than the SE sequence in terms of the border of sellar lesions, delineation of cranial nerves, and overall image quality; there was no significant difference regarding the boundary edge of the cavernous sinus and pituitary gland. In addition, the 3D-GRE sequence showed fewer pulsation artifacts but more susceptibility artifacts.

Conclusion

Our results indicate that 3D-GRE is the more suitable sequence for evaluating sellar lesions on contrast-enhanced T1-weighted imaging at 3.0 T.     

T2 mapping of hip articular cartilage in healthy volunteers at 3T: a study of topographic variation

PURPOSE: To perform baseline T2 mapping of the hips of healthy volunteers, focusing on topographic variation, because no detailed study has involved hips. T2 mapping is a quantitative magnetic resonance imaging (MRI) technique that evaluates cartilage matrix components. MATERIALS AND METHODS: Hips of 12 healthy adults (six men and six women; mean age = 29.5 +/- 4.9 years) were studied with a 3.0-Tesla MRI system. T2 measurement in the oblique-coronal plane used a multi-spin-echo (MSE) sequence. Femoral cartilage was divided into 12 radial sections; acetabular cartilage was divided into six radial sections, and each section was divided into two layers representing the superficial and deep halves of the cartilage. T2 of these sections and layers were measured. RESULTS: Femoral cartilage T2 was the shortest (-20 degrees to 20 degrees and -10 degrees to 10 degrees, superficial and deep layers), with an increase near the magic angle (54.7 degrees ). Acetabular cartilage T2 in both layers was shorter in the periphery than the other parts, especially at 20 degrees to 30 degrees. There were no significant differences in T2 between right and left hips or between men and women. CONCLUSION: Topographic variation exists in hip cartilage T2 in young, healthy adults. These findings should be taken into account when T2 mapping is applied to patients with degenerative cartilage.     

3D-TOF-MRA诊断偏侧面肌痉挛、三叉神经痛的病因

目的　研究增强三维体积扫描时间飞跃法磁共振血管成像 (3D -TOF -MRA)对偏侧面肌痉挛 (HFS)、三叉神经痛 (TN)病因诊断的临床价值。方法　常规颅脑MRI及增强 3D -TOF -MRA脑干薄层扫描 48例HFS患者和 46名对照、42例TN患者和 40名对照 ,盲法诊断面神经、三叉神经根部解剖改变 ,患者组与各自对照组作对照分析。结果　 (1)HFS、TN患者症状侧面神经根部、三叉神经根部受压迫 45侧 (93 .8% )和 3 6侧 (85 .7% ) ,其中血管压迫 44侧 (91.7% )和 3 2侧 (76.2 % ) ,肿瘤压迫 1侧 (2 .1% )和 4侧(8.9% ) ;无症状侧受血管压迫 8侧 (16.7% )和 4侧 (9.5 % ) ;对照组双侧受压迫 4侧 (4 .4% )和 5侧 (6.3 % )。 (2 )常见压迫面神经的血管为小脑前下动脉 (AICA) 17侧 (3 8.6% ) ,小脑后下动脉 (PICA) 12侧 (2 7.3 % ) ,椎动脉 (VA) 6侧 (13 .6% ) ;压迫三叉神经的血管为小脑上动脉 (SCA) 18侧 (5 6.3 % ) ,小脑前下动脉 (AICA) 5侧 (15 .6% ) ,起源不清的血管 (DIV) 4侧 (12 .5 % )。 (3 )面神经根部、三叉神经根部血管压迫发生HFS、TN的相对危险度估计值为 2 6.6和 9.84。 (4 )手术证实面肌痉挛组 3例、三叉神经痛组 6例神经血管压迫 ,面肌痉挛组 1例、三叉神经痛组 4例肿瘤压迫神经。结论　MRI加增强 3D -TOF -MRA     

Comparison of a single shot T1-weighted in- and out-of-phase magnetization prepared gradient recalled echo with a standard two-dimensional gradient recalled echo: preliminary findings

Purpose:

To compare in‐phase (IP) /out‐of‐phase (OP) single shot magnetization‐prepared gradient‐recalled‐echo (MP‐GRE) with a standard two‐dimensional gradient‐recalled‐echo (2D‐GRE), and to compare image quality of MP‐GRE in cooperative and noncooperative subjects.

Materials and Methods:

Ninety‐six consecutive subjects (52 males, 44 females; mean age, 53.2 ± 16.7 years), both cooperative (n = 73) and noncooperative (n = 23) subjects who had MRI examinations including precontrast T1‐weighted IP/OP MP‐GRE with or without IP/OP 2D‐GRE were included in the study. The sequences were independently qualitatively evaluated by two radiologists. Quantitative analysis of liver fat index, signal‐to‐noise ratio (SNR) and liver‐lesion contrast‐to‐noise ratio (CNR) was also performed. Data were subjected to statistical analysis.

Results:

The visual detection of the presence or absence of liver steatosis showed no differences between 2D‐GRE and MP‐GRE imaging (k = 1). Minor differences were observed on image quality between MP‐GRE and 2D‐GRE in cooperative subjects, and between MP‐GRE sequences performed in cooperative and noncooperative subjects. Liver fat index results were strongly positively correlated (r = .98; 95% confidence interval [CI] 0.97 to 0.98; P < .0001). Intercept (.14; 95% CI .13 to .15; P < .0001) and slope (.83; 95% CI .79 to .86; P < .0001) were statistically significant.

Conclusion:

IP/OP MP‐GRE and 2D‐GRE comparably demonstrate the presence or absence of hepatic steatosis. Image quality of MP‐GRE was also comparable to 2D‐GRE, and was not substantially adversely affected if subjects were unable to cooperate with breathholding instructions. J. Magn. Reson. Imaging 2011;33:1482–1490. © 2011 Wiley‐Liss, Inc.