Multislice dark-blood carotid artery wall imaging: a 1.5 T and 3.0 T comparison

PURPOSE: To compare two multislice turbo spin-echo (TSE) carotid artery wall imaging techniques at 1.5 T and 3.0 T, and to investigate the feasibility of higher spatial resolution carotid artery wall imaging at 3.0 T. MATERIALS AND METHODS: Multislice proton density-weighted (PDW), T2-weighted (T2W), and T1-weighted (T1W) inflow/outflow saturation band (IOSB) and rapid extended coverage double inversion-recovery (REX-DIR) TSE carotid artery wall imaging was performed on six healthy volunteers at 1.5 T and 3.0 T using time-, coverage-, and spatial resolution-matched (0.47 x 0.47 x 3 mm3) imaging protocols. To investigate whether improved signal-to-noise ratio (SNR) at 3.0 T could allow for improved spatial resolution, higher spatial resolution imaging (0.31 x 0.31 x 3 mm3) was performed at 3.0 T. Carotid artery wall SNR, carotid lumen SNR, and wall-lumen contrast-to-noise ratio (CNR) were measured. RESULTS: Signal gain at 3.0 T relative to 1.5 T was observed for carotid artery wall SNR (223%) and wall-lumen CNR (255%) in all acquisitions (P < 0.025). IOSB and REX-DIR images were found to have different levels of SNR and CNR (P < 0.05) with IOSB values observed to be larger. Normalized to a common imaging time, the higher spatial resolution imaging at 3.0 T and the lower spatial resolution imaging at 1.5 T provided similar levels of wall-lumen CNR (P = NS). CONCLUSION: Multislice carotid wall imaging at 3.0 T with IOSB and REX-DIR benefits from improved SNR and CNR relative to 1.5 T, and allows for higher spatial resolution carotid artery wall imaging.     

Improved suppression of plaque-mimicking artifacts in black-blood carotid atherosclerosis imaging using a multislice motion-sensitized driven-equilibrium (MSDE) turbo spin-echo (TSE) sequence

In this study, a turbo spin-echo (TSE) based motion-sensitized driven-equilibrium (MSDE) sequence was used as an alternative black-blood (BB) carotid MRI imaging scheme. The MSDE sequence was first optimized for more efficient residual blood signal suppression in the carotid bulb of healthy volunteers. Effective contrast-to-noise ratio (CNR_eff) and residual signal-to-noise ratio (SNR) in the lumen measured from MSDE images were then compared to those measured from inflow saturation (IS) and double inversion-recovery (DIR) images. Statistically significant higher CNR_eff and lower lumen SNR were obtained from MSDE images. To assess MSDE sequence in a clinical carotid protocol, 42 locations from six subjects with 50% to 79% carotid stenosis by duplex ultrasound were scanned with both MSDE and multislice DIR. The comparison showed that MSDE images present significantly higher CNR and lower lumen SNR compared to corresponding multislice DIR images. The vessel wall area and mean wall thickness measurements in MSDE images were slightly but significantly lower than those obtained with other blood suppression techniques. In conclusion, in vivo comparisons demonstrated that MSDE sequence can achieve better blood suppression and provide a more accurate depiction of the lumen boundaries by eliminating plaque mimicking artifacts in carotid artery (CA) imaging. Magn Reson Med 58:973–981, 2007. © 2007 Wiley-Liss, Inc.     

On the nature and reduction of plaque-mimicking flow artifacts in black blood MRI of the carotid bifurcation

Cardiac-gated black blood MRI of the carotid artery bifurcation in normal human subjects shows signal within the lumen suggesting wall thickening or atherosclerotic plaque. This signal was believed to be artifactual, arising from complex flow patterns present at the carotid bifurcation. Computer simulation of the hemodynamics and black blood multislice image acquisition in a model of the carotid bifurcation showed that these artifacts arise from spins recovering their signal within the slow, recirculating flow of the carotid bulb. The computed hemodynamics also suggested that these artifacts could be minimized or eliminated entirely by gating the acquisition of slices in the most artifact-prone region of the carotid bulb within a 250-ms window after peak systole. Application of these predictions to studies of normal volunteers showed that, in most cases, these flow artifacts in black blood MRI can be eliminated simply by altering the phase of the cardiac cycle to which the image acquisition is gated. The observation that the size and placement of the saturation slabs had little effect on these artifacts suggested that, in those cases in which recirculation persists throughout the cardiac cycle, either inversion-recovery or presaturation within the bulb itself would be required to suppress them.     

Parallel and nonparallel simultaneous multislice black-blood double inversion recovery techniques for vessel wall imaging

PURPOSE: To reduce long examination times of black-blood vessel wall imaging by acquiring multiple slices simultaneously and by using parallel acquisition techniques. MATERIALS AND METHODS: DIR-rapid acquisition with relaxation enhancement (RARE) techniques imaging up to 10 simultaneous slices per acquisition with single and multiple 180 degrees -reinversion pulses were developed. A slab-selective reinversion multislice DIR-RARE sequence incorporating generalized autocalibrating partially parallel acquisitions (GRAPPA) imaging was implemented. Four-channel and eight-channel carotid coils were built to test these sequences. A total of 11 subjects were studied. Contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) efficiency factor (SEF, SNR/unit time/slice) were measured from aortic images of three healthy subjects to determine optimal MR parameters. The DIR-RARE-GRAPPA sequence was run on aortas and carotid arteries of the five remaining healthy subjects and three atherosclerotic patients with optimal parameters (acquisition times 12-21 seconds). RESULTS: SEFs of slab-selective protocols were significantly higher than those of slice-selective protocols, and SEFs of DIR-RARE-GRAPPA protocols were significantly higher than corresponding non-GRAPPA protocols (P < 0.05). CNR was not significantly different for all imaging protocols. The DIR-RARE-GRAPPA multislice sequence showed 8.35-fold time improvement vs. single-slice DIR-2RARE sequence. CONCLUSION: Future MRI atherosclerotic plaque studies can be performed in substantially shorter times using these methods.     

Comparison between 2D and 3D high-resolution black-blood techniques for carotid artery wall imaging in clinically significant atherosclerosis

PURPOSE: To compare two- (2D) and three-dimensional (3D) black-blood imaging methods for morphological measurements of the carotid artery wall and atherosclerotic plaque. MATERIALS AND METHODS: A total of 18 subjects with 50% to 79% carotid stenosis were scanned with 2D (2-mm slice thickness) and 3D (1-mm/0.5-mm actual/interpolated slice thickness) T1-weighted fast spin-echo (FSE) black-blood imaging sequences with double inversion-recovery (DIR) blood suppression. Morphological measurements (lumen area, wall area, vessel area, mean wall thickness, and maximal wall thickness), signal-to-noise ratio (SNR) in the wall and lumen, and wall-lumen contrast-to-noise ratio (CNR) were compared between 2D and 3D images. The effect of improved slice resolution in 3D imaging was evaluated for visualization of small plaque components. RESULTS: Lumen SNR (P = 0.16), wall SNR (P = 0.65), and CNR (P = 0.94) were comparable between 2D/3D. There was no difference in average lumen area (P = 0.16), average wall area (P = 0.99), average vessel area (P = 0.0.58), mean wall thickness (P = 0.09), and maximum wall thickness (P = 0.06) between 2D/3D. Distributions of small plaque components such as calcification were better characterized by the 3D acquisition. There was a higher sensitivity to motion artifacts with 3D imaging, resulting in three examinations with low image quality. CONCLUSION: 2D and 3D protocols provided comparable morphometric measurements of the carotid artery. The major advantage of 3D imaging is improved small plaque component visualization, while the 2D technique provides higher reliability for image quality.     

Multicontrast black-blood MRI of carotid arteries: comparison between 1.5 and 3 tesla magnetic field strengths

PURPOSE: To compare black-blood multicontrast carotid imaging at 3T and 1.5T and assess compatibility between morphological measurements of carotid arteries at 1.5T and 3T. MATERIALS AND METHODS: Five healthy subjects and two atherosclerosis patients were scanned in 1.5T and 3T scanners with a similar protocol providing transverse T1-, T2-, and proton density (PD)-weighted black-blood images using a fast spin-echo sequence with single- (T1-weighted) or multislice (PD-/T2-weighted) double inversion recovery (DIR) preparation. Wall and lumen signal-to-noise ratio (SNR) and wall/lumen contrast-to-noise ratio (CNR) were compared in 44 artery cross-sections by paired t-test. Interscanner variability of the lumen area (LA), wall area (WA), and mean wall thickness (MWT) was assessed using Bland-Altman analysis. RESULTS: Wall SNR and lumen/wall CNR significantly increased (P < 0.0001) at 3T with a 1.5-fold gain for T1-weighted images and a 1.7/1.8-fold gain for PD-/T2-weighted images. Lumen SNR did not differ for single-slice DIR T1-weighted images (P = 0.2), but was larger at 3T for multislice DIR PD-/T2-weighted images (P = 0.01/0.03). The LA, WA, and MWT demonstrated good agreement with no significant bias (P 0.5), a coefficient of variation (CV) of < 10%, and intraclass correlation coefficient (ICC) of > 0.95. CONCLUSION: This study demonstrated significant improvement in SNR, CNR, and image quality for high- resolution black-blood imaging of carotid arteries at 3T. Morphologic measurements are compatible between 1.5T and 3T.     

Multislice double inversion-recovery black-blood imaging with simultaneous slice reinversion

PURPOSE: To develop a technique for time-efficient multislice double inversion-recovery (DIR) black-blood imaging and to test its applicability and limitations for high-resolution imaging of carotid arteries. MATERIALS AND METHODS: A multislice DIR pulse sequence with fast spin-echo (FSE) readout was implemented on a 1.5 T magnetic resonance (MR) scanner. The principle of the method is that a slice-selective inversion in a DIR preparation reinverts an entire slice pack, and all slices are imaged within repetition time (TR). The number of slices acquired per TR (N) controls the inversion time (TI) to execute the readout for each slice at the zero-crossing point of blood. Multislice DIR images (TR/TE = 2500/9 msec) of carotid arteries were obtained with variable N = 2-8 from four subjects. The method was compared with the standard single-slice DIR and inflow saturation techniques. RESULTS: Multislice DIR with N = 2-6 provided similar flow suppression in carotid arteries as single-slice DIR. At all N = 1-8, blood suppression by DIR was significantly better than by inflow saturation. An additional limitation of multislice DIR was saturation of the signal from stationary tissues that worsened visualization of the vessel wall at N >or= 6. CONCLUSION: Multislice DIR provides up to eight-fold improvement of time-efficiency relative to single-slice DIR and high-quality blood suppression.     

Effective blood signal suppression using double inversion-recovery and slice reordering for multislice fast spin-echo MRI and its application in simultaneous proton density and T2 weighted imaging

PURPOSE: To design a multislice double inversion-recovery fast spin-echo (FSE) sequence, with k-space reordered by inversion time at slice position (KRISP) technique, to produce black-blood vessel wall magnetic resonance imaging (MRI). MATERIALS AND METHODS: In this sequence, central k-space sampling for each slice is required at inversion time (TI) of the blood signal. To fill the entire k-space, the peripheral lines are obtained less or greater the TI and using a rotating slice order. Blood flow signal suppression was first evaluated using a phantom. Simulation studies were used to investigate FSE image quality. The final sequence was then applied to the rabbit abdominal aorta MRI at 4.7 T. RESULTS: In the flow phantom study, artifacts from slow-flowing water were substantially reduced by the KRISP technique; residual water spins were dephased by the strong phase-encoding gradient required for peripheral k-space. These dephased spins flowed into the slice plane where the center of k-space was being acquired at the TI of the flowing water signal. Multislice black-blood MR images were successfully obtained in the rabbit abdomen using the sequence with the k-trajectory optimized by the simulation study. CONCLUSION: The KRISP technique was effective both in multislice double inversion-recovery FSE and in blood signal suppression.     

Black-blood imaging of the human heart using rapid stimulated echo acquisition mode (STEAM) MRI

PURPOSE: To develop a rapid stimulated echo acquisition mode (STEAM) MRI technique for "black-blood" imaging of the human heart that overcomes the single-slice limitation and partially compromised blood suppression associated with double inversion-recovery techniques. MATERIALS AND METHODS: Black-blood multislice images of the heart along anatomic orientations and triggered to end diastole were obtained from healthy human subjects at 3T using rapid STEAM MRI sequences with five-eighths partial Fourier encoding and variable flip angles. Single-shot STEAM images at 2.5 x 2.5 mm2 in-plane resolution and 6-mm section thickness were recorded in 230 msec from individual heartbeats. Improved signal-to-noise ratio (SNR) and higher spatial resolution of 2.0 x 2.0 mm2 and 1.5 x 1.5 mm2 were achieved by segmented multishot STEAM MRI with interleaved k-space acquisitions (160 msec each) from several heartbeats. In a single breathhold covering 18 heartbeats selected applications employed either three segments with six sections or six segments with three sections. RESULTS: Because stimulated echoes (STEs) dephase signals from moving spins, rapid STEAM images are free from blood signal contamination. The method offers a flexible tradeoff between spatial resolution, imaging speed (i.e., number of segments), and volume coverage (i.e., number of sections). CONCLUSION: Rapid STEAM MRI of the heart emerges as a simple technique for multislice imaging of the myocardial wall with efficient flow suppression.     

Efficient flow suppressed MRI improves interscan reproducibility of carotid atherosclerosis plaque burden measurements

Purpose:

To determine if better flow suppression can meaningfully improve the reproducibility of measurements associated with carotid atherosclerotic disease, particularly for lumen and wall areas.

Materials and Methods:

Eighteen subjects with carotid artery stenosis identified by duplex ultrasound (11 with 16%–49% stenosis; 7 with 50%–79% stenosis) underwent two carotid magnetic resonance imaging (MRI) examinations on a 3T scanner with a 4‐channel phased array coil. High‐resolution intermediate‐weighted TSE (TR/TE = 4000/8.5 msec, 0.55 mm in‐plane resolution, 2 mm slice thickness, 16 slices, 3‐minute scan time) with two different flow‐suppression techniques (multislice double inversion recovery [mDIR] and motion‐sensitized driven‐equilibrium [MSDE]) were obtained separately. For each subject, bilateral arteries were reviewed. One radiologist blinded to timepoints, flow suppression techniques, and clinical information measured the arterial lumen area, wall area, and total vessel wall area.

Results:

Compared to mDIR, the MSDE technique had a smaller interscan standard deviation (SD) in lumen (SD: 3.6 vs. 5.2 mm², P = 0.02), wall area measurements (SD: 4.5 vs. 6.4 mm², P = 0.02), and a trend towards smaller SD in total vessel area measurement (SD: 4.4 vs. 4.9 mm², P = 0.07).

Conclusion:

The results from this study demonstrate that vessel wall imaging could quantify atherosclerotic plaque measurements more reliably with an improved blood suppression technique. This relationship between flow‐suppression efficiency and reproducibility of plaque measurements is important, as more reliable area measurements will be useful in clinical diagnosis and in serial MRI studies that monitor carotid atherosclerotic lesion progression and regression. J. Magn. Reson. Imaging 2010;32:452–458. © 2010 Wiley‐Liss, Inc.     

Carotid plaque signal differences among four kinds of T1-weighted magnetic resonance imaging techniques: A histopathological correlation study

Introduction

Several magnetic resonance (MR) imaging techniques are used to examine atherosclerotic plaque of carotid arteries; however, the best technique for visualizing intraplaque characteristics has yet to be determined. Here, we directly compared four kinds of T1-weighted (T1W) imaging techniques with pathological findings in patients with carotid stenosis.

Methods

A total of 31 patients who were candidates for carotid endarterectomy were prospectively examined using a 1.5-T MRI scanner, which produced four kinds of T1W images, including non-gated spin echo (SE), cardiac-gated black-blood (BB) fast-SE (FSE), magnetization-prepared rapid acquisition with gradient echo (MPRAGE), and source image of three-dimensional time-of-flight MR angiography (SI-MRA). The signal intensity of the carotid plaque was manually measured, and the contrast ratio (CR) against the adjacent muscle was calculated. CRs from the four imaging techniques were compared to each other and correlated with histopathological specimens.

Results

CRs of the carotid plaques mainly containing fibrous tissue, lipid/necrosis, and hemorrhage were significantly different with little overlaps (range: 0.92?C1.15, 1.22?C1.52, and 1.55?C2.30, respectively) on non-gated SE. However, BB-FSE showed remarkable overlaps among the three groups (0.89?C1.10, 1.07?C1.23, and 1.01?C1.42, respectively). MPRAGE could discriminate fibrous plaques from hemorrhagic plaques but not from lipid/necrosis-rich plaques: (0.77?C1.07, 1.45?C2.43, and 0.85?C1.42, respectively). SI-MRA showed the same tendencies (1.01?C1.39, 1.45?C2.57, and 1.12?C1.39, respectively).

Conclusion

Among T1W MR imaging techniques, non-gated SE images can more accurately characterize intraplaque components in patients who underwent CEA when compared with cardiac-gated BB-FSE, MPRAGE, and SI-MRA images.     

Prospective self-gating for swallowing motion: a feasibility study in carotid artery wall MRI using three-dimensional variable-flip-angle turbo spin-echo

Three-dimensional black-blood MRI is a promising noninvasive imaging technique for the assessment of atherosclerotic carotid artery disease. However, this technique is inherently susceptible to motion. In particular, swallowing can result in considerable wall motion at the carotid bifurcations, which may induce drastic image degradation or substantial overestimation of wall thickness. Self-gating techniques have previously been shown to be capable of resolving and compensating for cardiac or respiratory motion during MRI. This work presents a self-gating-based prospective motion gating scheme that is combined with a three-dimensional variable-flip-angle turbo spin-echo sequence (SPACE) for detecting swallowing motion. Self-gating signal readouts along the superior-inferior direction during each repetition time period are used to derive the projection profiles of the imaging volume. Based on cross-correlation analysis between the projection profiles and the corresponding reference profiles, swallowing motion can be detected and the motion-contaminated data will subsequently be discarded and reacquired in the next repetition time. The self-gated SPACE sequence was validated on eight healthy volunteers and two patients and, when compared with the conventional SPACE sequence, proved to be more resistant to swallowing motion and significantly improved image quality as well as the sharpness of carotid artery wall boundaries.     

MRI of heart morphology. Comparison of nongradient echo sequences with single- and multislice acquisition.

RATIONALE AND OBJECTIVES: A large variety of cardiac MRI sequences have been introduced for heart morphology evaluation. The aim of this study was to establish a practicable and robust examination protocol for standard high-field systems applying nongradient echo sequences with single- and multi-slice acquisition. METHODS: Fifty-one patients received electrocardiogramgated MRI of the heart with "black-blood" preparation, comparing three single-slice and three multislice sequences with a T1-weighted turbo spin echo reference sequence. Demarcation of the left ventricular myocardium and cavity and the extent of flow and motion artifacts were assessed. RESULTS: The myocardium and left ventricular cavity were depicted best with the single-slice T1- and T2-weighted turbo spin echo sequence. The nonbreath-hold multislice sequences produced marked artifacts and therefore were of poor diagnostic value. The TIRM haste sequence was best suited for fat suppression. The T2-weighted breath-hold single-shot sequence with half-Fourier imaging proved to be most appropriate for multislice imaging. CONCLUSIONS: Sufficient depiction of heart morphology with comprehensive evaluation of signal changes can be achieved using nongradient spin echo and turbo spin echo sequences with breath-holding. For rational imaging of myocardial and heart chamber morphology, multislice and single-slice sequences should be combined.     

Halting the effects of flow enhancement with effective intermittent zeugmatographic encoding (HEFEWEIZEN) in SSFP

Purpose

To describe a new method for performing dark blood (DB) magnetization preparation in TrueFISP (bSSFP) and apply the technique to high‐resolution carotid artery imaging.

Materials and Methods

The developed method (HEFEWEIZEN) provides directional flow suppression, while preserving bSSFP contrast, by periodically applying spatial saturation in short repetition time (TR) TrueFISP. Steady‐state free precession (SSFP) conditions are maintained throughout the acquisition for the imaging slice magnetization. HEFEWEIZEN was implemented on a 1.5 T scanner with standard receiver coils. Studies were performed in phantoms, eight asymptomatic volunteers, and two patients with low‐ and high‐grade carotid artery stenosis.

Results

Average flow suppression was 88% ± 4% (arterial) and 85% ± 3% (venous) in a multislice study. Stationary signal, contrast, and fine details were maintained with only slight signal suppression (11% ± 11%). Comparison to diffusion‐prepared SSFP in the common carotid artery demonstrated significant improvement in wall‐lumen contrast‐to‐noise ratio efficiency (P = 0.024). DB contrast was achieved with only 13% increased acquisition time (14.3 sec). Further acceleration was possible by confining the DB preparation to the central 60% of k‐space.

Conclusion

A fast, short TR, DB TrueFISP pulse sequence was developed and tested in the carotid arteries of asymptomatic volunteers and patients. J. Magn. Reson. Imaging 2009;29:1163–1174. © 2009 Wiley‐Liss, Inc.     

Simultaneous outer volume and blood suppression by quadruple inversion-recovery.

A new method has been developed for reduced field-of-view (FOV) imaging with simultaneous blood suppression. This method combines suppression of signals from the outer volume and inflowing blood by using a small-FOV quadruple inversion-recovery (SFQIR) preparative pulse sequence consisting of two double-inversion pulse pairs separated by appropriate delays. Within each pair, inversion pulses are successively applied to the imaged slice and the slab orthogonal to the imaging plane with the thickness equal to the FOV size in the phase-encoding direction. Each double inversion results in the reinversion of the magnetization in the central part of the FOV, while the outer areas of the FOV and inflowing blood remain inverted. The SFQIR module was implemented for single- and multislice acquisition with a fast spin-echo readout sequence. Based on a theoretical model of the signal, the timing parameters of the sequence corresponding to the maximal suppression efficiency can be found by minimizing the variation of the normalized signal over the entire range of T1's that occur in tissues. The method was tested for black-blood imaging of the aorta and carotid arteries, and the results demonstrated its ability to eliminate motion and flow artifacts, reduce scan time, and improve spatial resolution.     

3D volume-selective turbo spin echo for carotid artery wall imaging with navigator detection of swallowing

PURPOSE: To improve 3D volume-selective turbo spin echo (TSE) carotid artery wall imaging by incorporating navigators to reduce artifacts caused by swallowing. MATERIALS AND METHODS: Images were acquired on a Siemens Magnetom Sonata 1.5T scanner. 3D volume-selective TSE scans of the carotid arteries were acquired in six healthy volunteers. A cross-pair navigator placed on the back of the tongue was used to detect swallowing and movement. Two swallowing patterns were tested: 1) a single swallow approximately halfway through the scan time, at the center of k(z), and 2) repeated swallowing as often as possible throughout the scan period. Images were acquired with and without navigators for comparison. Signal intensity in the lumen was quantified for the quality of blood suppression, and the clarity of the vessel wall in the common carotid was ranked by four independent blinded observers. RESULTS: In general, lower signal intensity was recorded in the lumen, and decreased blurring and ghosting were observed on scans with navigator control. This reduction in lumen signal intensity signifies an improvement in the black-blood imaging technique. The differences likely reflect the improved double inversion/blood suppression efficiency due to cycles being rejected when the heart rate changed at the point of swallowing, or decreased motional blurring/ghosting of tissue when the navigator is used, or a combination of these two effects. A statistical analysis of image quality showed a significant difference between navigated and non-navigated scans as scored by four independent, blinded observers. For both swallowing patterns, the mean score for the navigator images was on average 0.6 greater than that of non-navigator images (on a scoring scale of 0-5, where 0 = no vessel visible, and 5 = good delineation and blood suppression) and P-values for all observers were less than 0.01. Overall, the central swallow scans were scored higher than the repeated swallow scans. One reason for this may be the fact that the heart rate increased on swallowing, and this often lasted for one or two cardiac cycles after the navigator returned to the normal acceptance position. The effect of the increased heart rate after swallowing is likely to have an effect on double inversion blood suppression efficiency. Therefore, the increased amount of heart rate changes with repeated swallowing may have a greater adverse effect, even if the navigator rejects data views during the swallowing motion. CONCLUSION: The clarity of vessel wall delineation and the apparent efficiency of blood suppression are reduced by swallowing during acquisition. Both motion blurring and quality of blood suppression are factors that can be improved with the use of a navigator accept/reject method.     

Is the addition of ECG gating to technetium-99m sestamibi SPET of value in the assessment of myocardial viability?

The main goal of this study was to evaluate whether the addition of ECG gating to technetium-99m sestamibi single-photon emission tomography (SPET) perfusion imaging assists the prediction of recovery of regional wall motion abnormalities after revascularization. Thirty-six patients with coronary artery disease were included in the study. All had wall motion abnormalities, and 31 (86%) had a clinical history of myocardial infarction. Coronary artery bypass surgery was performed in 18 patients and angioplasty in the remainder. All underwent ECG-gated and non-gated SPET at rest and after intravenous dipyridamole. Two-dimensional echocardiography was performed at a mean of 27 days before revascularization and at a mean of 69 days following revascularization to assess segmental wall motion changes. Perfusion prior to revascularization was analysed qualitatively and quantitatively on gated and non-gated SPET, and the results compared with those of echocardiography. Bullseye parameters were obtained from a normal database, generated from data in 40 normal volunteers, using dipyridamole ECG-gated and non-gated sestamibi SPET. There was good concordance between gated and non-gated qualitative analysis (79% with kappa=0.65) for normal, viable or necrotic segments. Gated SPET predicted functional recovery in 27 of 35 (77%) segments showing echocardiographic improvement while non-gated SPET did so in 30 of 39 (77%) such segments. Gated SPET predicted no functional recovery in 20 of 45 (44%) segments that did not show improved wall motion after revascularization, while with non-gated SPET the figure was 18 of 51 (35%). The positive predictive values of gated and non-gated SPET with regard to the recovery of wall motion following revascularization were 52% and 48%, while the negative predictive values were 71% and 67%, respectively.^99mTc-sestamibi had a low predictive value for recovery of function if visual assessment was used in the analysis of SPET data. Quantitative bullseye sestamibi parameters (defect extension and severity, reversibility and percentage change in extension), from gated or non-gated studies, appear best to distinguish which segments will display improved motility on the echocardiogram after revascularization. The addition of ECG gating does not significantly increase the predictive value of SPET imaging with regard to recovery of function.     

Detection of Carotid Artery Stenosis: A Comparison between 2 Unenhanced MRAs and Dual-Source CTA

BACKGROUND AND PURPOSE:Dual-source CTA and black-blood MRA are recently developed techniques for evaluating carotid stenosis. The purpose of this study was to compare dual-source CTA with black-blood MRA and conventional TOF MRA in both detecting carotid stenosis by using DSA as a reference standard and demonstrating plaque morphology.MATERIALS AND METHODS:Thirty patients with suspected carotid artery stenosis underwent unenhanced MRA by using black-blood and TOF MRA and dual-source CTA. Source images from unenhanced MRAs and dual-source CTA were reconstructed with MIP or curved planar reconstruction. The degree of carotid artery stenosis was measured, and plaque surface morphology at the stenosis was analyzed and compared among different techniques.RESULTS:Good correlation was observed for measuring the degree of carotid stenosis among dual-source CTA, black-blood MRA, TOF MRA, and DSA. Sensitivity and specificity for detecting severe stenosis were 100% and 97% with dual-source CTA, 100% and 95% with black-blood MRA, and 79% and 95% with TOF MRA. None of the 3 technologies resulted in stenosis of <50% being overestimated. Plaque surface irregularity or ulceration was more frequently detected with dual-source CTA and black-blood MRA than with TOF MRA and DSA.CONCLUSIONS:This preliminary study shows that black-blood MRA is a promising technique, comparable with dual-source CTA and DSA, but better than TOF MRA, in the evaluation of carotid stenosis. Unlike dual-source CTA, black-blood MRA requires no intravenous contrast or radiation.

Carotid artery atherosclerosis is a major cause of ischemic cerebrovascular disease.^1,2 Measurement of carotid stenosis and demonstration of plaque morphology are critical for the management of patients with carotid atherosclerosis. DSA is the current reference standard for evaluating carotid artery stenosis. The diagnostic role of DSA has largely been replaced, however, by noninvasive techniques such as sonography, CTA, and MRA.Sonography has been the most commonly performed technique but may be restricted by its operator dependence and limited coverage. CTA is another widely used technique for the evaluation of carotid artery stenosis with high accuracy.³ Dual-source CTA (DSCTA) uses 2 x-ray sources and 2 detectors at the same time. With this technique, 2 images can be simultaneously acquired with different tube voltages; this feature has been shown to be an advantage for the evaluation of densely calcified carotid stenosis.^4,5 Contrast-enhanced MRA has been established as an alternative for carotid imaging with a diagnostic accuracy similar to that of CTA.^6,7 Both CTA and contrast-enhanced MRA use contrast media and are restricted in patients with impaired renal function, and CTA also requires ionizing radiation. As a result, unenhanced MRA without gadolinium is a desirable alternative, especially in patients with renal failure. Conventional TOF MRA has been widely used in clinical practice for carotid visualization, but it is limited by local reduction of signal intensity related to slow and turbulent flow and also prolonged imaging time.⁸ T2-weighted black-blood MRA (BB MRA) is a newly developed technique showing potential in the evaluation of both the lumen and the wall of the carotid artery after optimal suppression of the signal from flowing blood.^9,10 Few studies, to our knowledge however, have compared DSCTA with BB MRA and conventional TOF MRA in evaluating carotid stenosis.The aim of this study was to prospectively and intraindividually compare these 2 unenhanced MRA methods with DSCTA in detecting carotid artery stenosis by using DSA as the standard of reference and in demonstrating plaque morphology.     

Water excitation: a possible pitfall in cerebral time-of-flight angiography

BACKGROUND AND PURPOSE: Time-of-flight MR angiography (TOF MRA), with its advantage of high spatial resolution, is widely used for visualization of intracranial arteries. Fat signal intensity from bone marrow can interfere with vessel signal intensity, especially in maximum intensity projection reconstructions. Use of a technique such as fat saturation or water excitation can reduce this signal intensity. METHODS: Ten volunteers were included in this study. TOF MRA was performed by using spoiled gradient echo sequences on a 1.5-T MR unit either with or without water excitation. Water excitation was performed by using a binomial excitation pulse pair, with a null in the excitation profile at the fat frequency to obtain fat suppression. Two blinded neuroradiologists then judged the images. Additional studies by using a phantom with a flow of about 2 mL/s were performed under the same conditions. Image quality obtained with and that without water excitation was graded as similar by both neuroradiologists. RESULTS: As the main finding, the sequences by using water excitation revealed an important pitfall: apparent carotid artery stenosis was detected in 4/10 and occlusions in 1/10 cases. Use of a flow phantom could reveal the same pitfall. Intracranial vessel disease was excluded in all volunteers by using Doppler sonography. CONCLUSION: The type of water excitation tested here can induce significant artifacts in cerebral TOF MRA. These artifacts can be misinterpreted as carotid artery stenosis or even occlusion, whereas the benefit brought by water excitation with respect to fat suppression is less significant.     

Three-dimensional black-blood MR imaging of carotid arteries with segmented steady-state free precession: initial experience

This HIPAA-compliant study had institutional review board approval. Informed consent was obtained. The purpose was to prospectively evaluate a segmented three-dimensional (3D) double inversion recovery (DIR)-prepared steady-state free precession (SSFP) magnetic resonance (MR) imaging sequence for fast high-spatial-resolution black-blood carotid arterial wall imaging. Carotid wall-lumen contrast-to-noise ratio (CNR) obtained with this sequence was compared with those obtained with two-dimensional (2D) single- and multisection black-blood fast spin-echo (SE) sequences. MR imaging of both carotid artery bifurcations over 3 cm of transverse coverage was performed in eight volunteers (seven men, one woman; age range, 26-56 years) with no known history of carotid artery disease. Adjusted for section thickness and imaging time per section, higher effective mean CNR was achieved with segmented 3D DIR-prepared SSFP than with single-section 2D DIR-prepared fast SE or multisection 2D saturation-band fast SE (P < .05). Segmented 3D DIR-prepared SSFP enables black-blood carotid arterial wall MR imaging with contiguous thin-section coverage and greater imaging speed and effective CNR than conventional 2D fast SE techniques.