Carotid arterial wall MRI at 3T using 3D variable‐flip‐angle turbo spin‐echo (TSE) with flow‐sensitive dephasing (FSD)

Purpose:

To evaluate the effectiveness of flow‐sensitive dephasing (FSD) magnetization preparation in improving blood signal suppression of three‐dimensional (3D) turbo spin‐echo (TSE) sequence (SPACE) for isotropic high‐spatial‐resolution carotid arterial wall imaging at 3T.

Materials and Methods:

The FSD‐prepared SPACE sequence (FSD‐SPACE) was implemented by adding two identical FSD gradient pulses right before and after the first refocusing 180°‐pulse of the SPACE sequence in all three orthogonal directions. Nine healthy volunteers were imaged at 3T with SPACE, FSD‐SPACE, and multislice T2‐weighted 2D TSE coupled with saturation band (SB‐TSE). Apparent carotid wall‐lumen contrast‐to‐noise ratio (aCNR_w‐l) and apparent lumen area (aLA) at the locations with residual‐blood (rb) signal shown on SPACE images were compared between SPACE and FSD‐SPACE. Carotid aCNR_w‐l and lumen (LA) and wall area (WA) measured from FSD‐SPACE were compared to those measured from SB‐TSE.

Results:

Plaque‐mimicking flow artifacts identified in seven carotids on SPACE images were eliminated on FSD‐SPACE images. The FSD preparation resulted in slightly reduced aCNR_w‐l (P = 0.025), but significantly improved aCNR between the wall and rb regions (P < 0.001) and larger aLA (P < 0.001). Compared to SB‐TSE, FSD‐SPACE offered comparable aCNR_w‐l with much higher spatial resolution, shorter imaging time, and larger artery coverage. The LA and WA measurements from the two techniques were in good agreement based on intraclasss correlation coefficient (0.988 and 0.949, respectively; P < 0.001) and Bland‐Altman analyses.

Conclusion:

FSD‐SPACE is a time‐efficient 3D imaging technique for carotid arterial wall with superior spatial resolution and blood signal suppression. J. Magn. Reson. Imaging 2010;31:645–654. © 2010 Wiley‐Liss, Inc.     

A comparison between NASCET and ECST methods in the study of carotids: Evaluation using Multi-Detector-Row CT angiography

Purpose

NASCET and ECST systems to quantify carotid artery stenosis use percent diameter ratios from conventional angiography. With the use of Multi-Detector-Row CT scanners it is possible to easily measure plaque area and residual lumen in order to calculate carotid stenosis degree. Our purpose was to compare NASCET and ECST techniques in the measurement of carotid stenosis degree by using MDCTA.

Methods and material

From February 2007 to October 2007, 83 non-consecutive patients (68 males; 15 females) were studied using Multi-Detector-Row CT. Each patient was assessed by two experienced radiologists for stenosis degree by using both NASCET and ECST methods. Statistic analysis was performed to determine the entity of correlation (method of Pearson) between NASCET and ECST. The Cohen kappa test and Bland-Altman analysis were applied to assess the level of inter- and intra-observer agreement.

Results

The correlation Pearson coefficient between NASCET and ECST was 0.962 (p < 0.01). Intra-observer agreement in the NASCET evaluation, by using Cohen statistic was 0.844 and 0.825. Intra-observer agreement in the ECST evaluation was 0.871 and 0.836. Inter-observer agreement in the NASCET and ECTS were 0.822 and 0.834, respectively. Agreement analysis by using Bland-Altman plots showed a good intra-\inter-observer agreement for the NASCET and an optimal intra-\inter-observer agreement for the ECST.

Conclusions

Results of our study suggest that NASCET and ECST methods show a strength correlation according to quadratic regression. Intra-observer agreement results high for both NASCET and ECST.     

T1‐weighted–SPACE dark blood whole body magnetic resonance angiography (DB‐WBMRA): Initial experience

Purpose:

To evaluate the feasibility of the dark blood fast spin echo (FSE) T1‐weighted–Sampling Perfection with Application of optimized Contrasts using different flip angle Evolution (T1w‐SPACE) sequence in assessing whole body arterial wall information from the extracranial carotids to the popliteal artery.

Materials and Methods:

Twenty‐eight subjects were subjected to noncontrast, dark blood whole body magnetic resonance angiography (DB‐WBMRA) using a T1w‐SPACE sequence optimized for each of the individual stations: carotid artery, thoracic aorta, abdominal aorta, and thigh/superficial femoral artery (SFA). Image quality/vessel wall visualization and the time required to image the four stations were evaluated. Two observers checked the reproducibility of vessel wall depiction by performing quantitative measurements in registered initial and repeat studies (six subjects) of vessel wall and lumen area at 17 locations along the arterial tree.

Results:

In 25 of the 28 scanned subjects, dark blood arterial images acquired in approximately 1 hour total imaging time allowed whole body arterial vessel wall visualization. Quantitative measurements showed high correlation between the initial and repeat studies for each of the observers as well as high interobserver reproducibility (r > 0.95; P < 0.01).

Conclusion:

DB‐WBMRA using T1w‐SPACE is feasible and can be performed with a high degree of reliability. J. Magn. Reson. Imaging 2010; 31: 502–509. © 2010 Wiley‐Liss, Inc.     

Carotid stenosis measurement on colour Doppler ultrasound: agreement of ECST, NASCET and CCA methods applied to ultrasound with intra-arterial angiographic stenosis measurement

PURPOSE: Carotid stenosis is usually determined on Doppler ultrasound from velocity readings. We wondered if angiography-style stenosis measurements applied to ultrasound images improved accuracy over velocity readings alone, and if so, which measure correlated best with angiography. MATERIALS AND METHODS: We studied prospectively patients undergoing colour Doppler ultrasound (CDU) for TIA or minor stroke. Those with 50%+ symptomatic internal carotid artery (ICA) stenosis had intra-arterial angiography (IAA). We measured peak systolic ICA velocity, and from the ultrasound image, the minimal residual lumen, the original lumen (ECST), ICA diameter distal (NASCET) and CCA diameter proximal (CCA method) to the stenosis. The IAAs were measured by ECST, NASCET and CCA methods also, blind to CDU. RESULTS: Amongst 164 patients (328 arteries), on CDU the ECST, NASCET and CCA stenosis measures were similarly related to each other (ECST = 0.54 NASCET + 46) as on IAA (ECST = 0.6 NASCET + 40). Agreement between CDU- and IAA-measured stenosis was similar for ECST (r = 0.51), and CCA (r = 0.48) methods, and slightly worse for NASCET (r = 0.41). Adding IAA-style stenosis to the peak systolic ICA velocity did not improve agreement with IAA over peak systolic velocity alone. CONCLUSION: Angiography-style stenosis measures have similar inter-relationships when applied to CDU, but do not improve accuracy of ultrasound over peak systolic ICA velocity alone.     

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.     

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.     

How should we estimate carotid stenosis using magnetic resonance angiography?

Our purpose was to assess the reproducibility of and differences between the most commonly used methods for assessing carotid artery stenosis using magnetic resonance angiography (MRA). We studied 55 patients who underwent axial three-dimensional time-of-flight MRA (1.5 T). Quantitative caliper measurements were performed from maximum intensity projection (MIP) and multiple planar reconstruction (MPR) images, according to the criteria of the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and European Carotid Surgery Trial (ECST). The measurements were compared to each other and to visual interpretation, using conventional angiography as the reference. The measured percentage stenoses were higher on MRA than on digital subtraction angiography (DSA) using both NASCET (mean difference 1.9–3.0%) and ECST (6.3–6.7%) criteria. The kappa coefficients for the agreement between DSA and MRA were higher using the NAS-CET (0.61–0.76) than the ECST criteria (0.52–0.65). No statistically significant differences were found between measurements from MIP and MPR images. The ECST measurement criteria gave significantly higher percentage stenoses than the NASCET criteria (P<0.001), this difference being more prominent on MRA (mean difference in diameter stenosis percentage 14.3–16.4%) than on DSA (7.6–11.2%) and most important with mild stenoses. The difference between visual interpretation and quantitative measurements on MRA was significant (P=0.01–0.001). There were no statistically significant interobserver differences in the MRA film readings, either in visually estimated degrees of stenosis or stenosis measurements. Thus, the different criteria of the two multicentre trials led to significantly different results, especially in the assessment of mild stenosis, and these differences are more important with MRA than with aging modalities or the reconstruction programs seem less important.     

Carotid stenosis degree in CT angiography: assessment based on luminal area versus luminal diameter measurements

The aim of this study was to investigate CT angiography (CTA) luminal area measurements in the assessment of carotid artery stenosis compared with the current clinically used criteria based on lumen diameter measurements. Seventy-two vessels in 36 patients were evaluated by CTA and digital subtraction angiography (DSA). Two observers measured area and diameter stenosis degrees using automated 3D CTA analysis software. The ratio of the largest/smallest luminal diameter at the level of maximal stenosis (L/S ratio) was used to describe lumen morphology. Diagnostic agreement between CTA and DSA was calculated. For the assessment of area stenosis, interobserver and intraobserver correlation coefficients were 0.898 and 0.906 (p<0.001). The correlation coefficient between the diameter stenosis and area stenosis was lower in stenoses with extremely noncircular lumen (L/S ratio 1.5) (r=0.797, p<0.001) compared with stenoses with circular lumen (LS ratio <1.2) (r=0.978, p<0.001). Only satisfactory agreement ( 0.54-0.77, p<0.001) was obtained between area stenosis on CTA and diameter stenosis on DSA. Assessment of stenosis degree with area measurements on 3D CTA proved to be reproducible. Area stenosis provides a less-severe estimate of the degree of carotid stenosis but might theoretically express the real hemodynamic significance of the lesion better than diameter stenosis, especially in stenoses with noncircular lumen.     

Single-dose time-resolved contrast enhanced hybrid MR angiography in diagnosis of peripheral arterial disease: compared with digital subtraction angiography

Purpose:

To validate cardiovascular magnetic resonance (CMR) arterial wall volume measurement using whole arterial specimens ex vivo.

Materials and Methods:

Twenty cadaveric carotid arteries (from 10 patients) were fixed in formaldehyde and imaged with a clinical T1‐weighted 2D CMR sequence and, for imaging validation, with a high‐resolution 3D sequence. Histological validation was performed by sectioning the arteries and microscopically determining area and volume.

Results:

Comparison between the clinical 2D CMR sequence and the 3D high‐resolution validation sequence showed equivalent luminal volumes (889 vs. 880 mm³; P = 0.54; R² = 0.99), and slightly higher 2D CMR arterial wall volumes (982 vs. 916 mm³; +7%; P < 0.01; R² = 0.96) and adventitial volumes (1901 vs. 1826 mm³; +4%; P < 0.01; R² = 0.99). Comparison between 2D CMR and microscopy, performed over a similar longitudinal extent of vessel, showed slightly higher 2D CMR volumes for the lumen (354 vs. 308 mm³; +14%; P < 0.01; R² = 0.97), arterial wall (388 vs. 351 mm³; +10%; P < 0.01; R² = 0.97) and total volumes (750 vs. 665 mm³; +12%; P < 0.01; R² = 0.95).

Conclusion:

The accuracy of the clinical 2D CMR vessel wall sequence for measuring carotid lumen, adventitial, and wall volumes is good against ex vivo measurements, with minor overestimation. This study validates carotid arterial wall quantification by CMR for atherosclerosis research. J. Magn. Reson. Imaging 2010;31:935–941. ©2010 Wiley‐Liss, Inc.     

Measurement of common carotid artery lumen dynamics during the cardiac cycle using magnetic resonance TrueFISP cine imaging

Purpose

To demonstrate magnetic resonance (MR) measurements of vascular lumen dynamics in common carotid arteries by using true fast imaging with steady‐state precession (TrueFISP) cine imaging with an aim to provide additional physiologic information on the vessels.

Materials and Methods

The left and right common carotid arteries were studied in normal young men (N = 6; age = 21–24 years; body weight = 130–175 lbs) using electrocardiogram (ECG)‐triggered TrueFISP cine imaging at 20 frames per cardiac cycle. Lumen area waveforms were characterized with specific time and amplitude ratios. Distension values were quantified.

Results

Distension values were measured at 25.92 ± 2.58% and 27.58 ± 4.44% for the left and right common carotid arteries, respectively. These findings are consistent with those previously documented using ultrasound imaging in a similar age group. Consistent lumen area waveform characteristics were found among the subjects studied.

Conclusion

These findings demonstrate for the first time that the use of TrueFISP cine imaging is a robust, rapid technique for quantifying carotid lumen area dynamics and distension, which may be valuable in characterizing and diagnosing cardiovascular diseases. J. Magn. Reson. Imaging 2008;28:1527–1532. © 2008 Wiley‐Liss, Inc.     

Classification of carotid stenosis by millimeter CT angiography measures: effects of prevalence and gender

BACKGROUND AND PURPOSE: Previous studies quantifying moderate and severe carotid stenosis by direct millimeter measures on CT angiography (CTA) did not consider how prevalence and gender may influence classification cutoff values.MATERIALS AND METHODS: Three hundred nineteen carotid arteries were evaluated in consecutive patients with known or suspected carotid artery disease. Millimeter measures were obtained of the stenotic carotid bulb lumen and distal internal carotid artery (ICA). Interclass correlation coefficients (ICC) defined interobserver and intraobserver agreement. North American Symptomatic Carotid Endarterectomy Trial (NASCET)-style percent stenosis ratios were calculated per carotid artery and used in linear regression and receiver operating characteristic (ROC) curve analysis to define equivalent millimeter quantification and classification values. Likelihood ratios and prevalence-specific positive/negative predictive values (PPV/NPV) were calculated to determine the most appropriate millimeter cutoff values to classify stenosis.RESULTS: Interobserver agreement was excellent for stenosis measures (0.90) and good for distal ICA measures (0.79). Gender-specific regression curves and ROC curves indicated that millimeter stenosis is an excellent tool to quantify and classify carotid stenosis. Assuming a 10% prevalence of severe stenosis, we found that the cutoff value maximizing NPV and PPV was 1.1 mm for both genders (female: PPV = 86.2, NPV = 97.7; male: PPV = 83.2, NPV = 95.9). Assuming a 40% prevalence of moderate stenosis, we found that the cutoff values differed between genders: female = 2.0 mm (PPV = 91.3, NPV = 91.5), male = 2.1 mm (PPV = 91.6, NPV = 92.4). Specific millimeter cutoffs will vary depending upon the clinical scenario, prevalence, and gender.CONCLUSIONS: Direct millimeter stenosis measures are an excellent tool to classify moderate and severe carotid artery stenosis. Millimeter classification cutoff values that best approximate NASCET classifications vary depending on prevalence and gender.

There is a linear relationship between direct millimeter carotid stenosis measures on CT angiography (CTA) and derived percent stenosis as defined by the North American Symptomatic Carotid Endarterectomy Trial (NASCET).^1–3 This linear relationship allows prediction of NASCET-style percent stenosis from a single direct millimeter measure of stenosis. Quantification of carotid stenosis based on a direct stenosis measure is easy, fast, and reliable.¹ In addition to eliminating the need for ratio calculations, a direct stenosis measure eliminates the variability of NASCET-style ratios due to differences in distal ICA size within and among patients.Beyond quantification of stenosis, the NASCET ratio has been used to categorize carotid stenosis as moderate (≥50%–69%) and severe (≥70%). Because millimeter stenosis measures can predict NASCET-style ratios, it could be implied that specific millimeter values may similarly classify carotid artery disease. Prior studies have reported such millimeter classification thresholds, along with their respective sensitivity and specificity values.¹ However, the sensitivity and specificity values of these millimeter stenosis classifications were <100%. The implication of this difference is that the previously defined millimeter stenosis thresholds are misclassifying some cases of carotid disease.To decrease the degree of misclassifications from the millimeter stenosis measures, classification threshold values should maximize the positive and negative predictive values (PPV, NPV) of the test. A PPV (the probability that the results in a patient with a positive test result are truly positive) of the test depends not only on the sensitivity and specificity of the test but also on the prevalence of the “condition” within the population being studied. The “condition” in this case is the prevalence of moderate and severe stenosis, as defined by NASCET ratios. The potential impact that gender-specific prevalence could have on the accuracy of millimeter stenosis categorization, in substitution for calculating a NASCET ratio, is an important feature to consider before implementing a change in practice.     

Scan‐rescan reproducibility of carotid atherosclerotic plaque morphology and tissue composition measurements using multicontrast MRI at 3T

Purpose:

To evaluate interscan reproducibility of both vessel morphology and tissue composition measurements of carotid atherosclerosis using a fast, optimized, 3T multicontrast protocol.

Materials and Methods:

A total of 20 patients with carotid stenosis >15% identified by duplex ultrasound were recruited for two independent 3T MRI (Philips) scans within one month. A multicontrast protocol including five MR sequences was applied: TOF, T1‐/T2‐/PD‐weighted and magnetization‐prepared rapid acquisition gradient‐echo (MP‐RAGE). Carotid artery morphology (wall volume, lumen volume, total vessel volume, normalized wall index, and mean/maximum wall thickness) and plaque component size (lipid rich/necrotic core, calcification, and hemorrhage) were measured over two time points.

Results:

After exclusion of images with poor image quality, 257 matched locations from 18 subjects were available for analysis. For the quantitative carotid morphology measurements, coefficient of variation (CV) ranged from 2% to 15% and intraclass correlation coefficient (ICC) ranged from 0.87 to 0.99. Except for maximum wall thickness (ICC = 0.87), all ICC were larger than 0.90. For the quantitative plaque composition measurements, the ICC of the volume and relative content of lipid rich/necrotic core and calcification were larger than 0.90 with CV ranging from 22% to 32%.

Conclusion:

The results from the multicontrast high‐resolution 3T MR study show high reliability for carotid morphology and plaque component measurements. 3T MRI is a reliable tool for longitudinal clinical trials, with shorter scan time compared to 1.5T. J. Magn. Reson. Imaging 2010;31:168–176. © 2009 Wiley‐Liss, Inc.     

Depicting the semicircular canals with inner‐ear MRI: A comparison of the SPACE and TrueFISP sequences

Purpose:

To assess the ability of magnetic resonance imaging (MRI) to depict the semicircular canals of the inner ear by comparing results from the sampling perfection with application‐optimized contrasts by using different flip angle evolutions (SPACE) sequence with those from the true free induction with steady precession (TrueFISP) sequence.

Materials and Methods:

A 1.5‐T MRI system was used to perform an in vivo study of 10 healthy volunteers and 17 patients. A three‐point visual score was employed for assessing the depiction of the semicircular canals and facial and vestibulocochlear nerves and the contrast‐to‐noise ratio (CNR) was computed for the vestibule and pons on images with the SPACE and TrueFIPS sequences.

Results:

There were no susceptibility artifact‐related filling defects with the SPACE sequence. However, the TrueFISP sequence showed filling defects for at least one semicircular canal on both sides in seven cases for healthy subjects and in 10 cases for patients. The CNR with the SPACE sequence was significantly higher than with the TrueFISP sequence (P < 0.05). There was no statistically significant difference in depicting the facial and the vestibulocochlear nerves (P = 0.32).

Conclusion:

For the depiction of the semicircular canal, the SPACE sequence is superior to the TrueFISP sequence. J. Magn. Reson. Imaging 2013;37:652–659. © 2012 Wiley Periodicals, Inc.     

Unenhanced ECG-gated fast spin-echo MR digital subtraction angiography (MRDSA) using short echo-spacing three-dimensional sequence of femoral arteries: initial experience

Purpose:

To compare the image qualities of unenhanced electrocardiographically (ECG)‐gated fast spin‐echo magnetic resonance digital subtraction angiography (MRDSA) using a short echo‐spacing three‐dimensional (3D) sequence, known as sampling perfection with application‐optimized contrasts using different flip angle evolutions (SPACE), and the conventional half‐Fourier single‐shot turbo spin‐echo (HASTE) sequence.

Materials and Methods:

Unenhanced ECG‐gated MRDSA using SPACE and HASTE of the femoral arteries were prospectively acquired in 13 healthy volunteers at 1.5 Tesla (T) MRI. Sequential frontal maximum‐intensity‐projection images produced by subtracting each of 10 systolic images from a diastolic image were evaluated quantitatively using paired t‐test and qualitatively by two blinded radiologists using the Mann‐Whitney U‐test.

Results:

Quantitatively, relative contrast against the background, contour sharpness index, and slope of the sequential signal changes of the superficial femoral artery of MRDSA using SPACE were significantly better than those of HASTE (P = 0.005, P = 0.001, and P < 0.0001, respectively). Qualitatively, the overall subjective image quality and sequential appearance changes of MRDSA using SPACE were significantly better than those of HASTE (P < 0.0001 and P < 0.0001, respectively).

Conclusion:

Unenhanced ECG‐gated fast spin‐echo MRDSA using SPACE produces increments in signal intensity, which reflect arterial pulse wave transmission, more clearly than the conventional HASTE sequence. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

T2-weighted cardiac MR assessment of the myocardial area-at-risk and salvage area in acute reperfused myocardial infarction: comparison of state-of-the-art dark blood and bright blood T2-weighted sequences

Purpose:

To compare different state‐of‐the‐art T2‐weighted (T2w) imaging sequences combined with late gadolinium enhancement (LGE) for myocardial salvage area (MSA) assessment by cardiac magnetic resonance (CMR). T2w imaging has been used to assess the myocardial area at risk (AAR) in acute myocardial infarction (AMI) patients, but its clinical application is challenging due to technical and physical limitations.

Materials and Methods:

Thirty patients with reperfused AMI underwent complete CMR imaging 2–5 days after hospital admission. Myocardial AAR and MSA were quantified on four different T2w sequences: (a) free‐breathing T2‐prepared single‐shot balanced steady‐state free precession (T2p_ssbSSFP); (b) breathhold T2‐weighted acquisition for cardiac unified T2 edema (ACUTE); (c) breathhold T2w dark‐blood inversion recovery turbo‐spin echo (IR‐TSE) (short‐term inversion recovery: STIR); and (d) free‐breathing high‐resolution T2 dark‐blood navigated BLADE. The diagnostic performance of each technique was also assessed.

Results:

Quantitative analysis showed significant differences in myocardial AAR extent as quantified by the four T2w sequences (P < 0.05). There were also significant differences in sensitivity, specificity and overall diagnostic performance.

Conclusion:

Detection and quantification of AAR, and thus of MSA, by T2wCMR in reperfused AMI patients varied significantly between different T2w sequences in the same clinical setting. J. Magn. Reson. Imaging 2012;328‐339. © 2011 Wiley Periodicals, Inc.     

Impact of T2 decay on carotid artery wall thickness measurements

Purpose:

To investigate the impact of T2 relaxation of the carotid wall on measurements of its thickness.

Materials and Methods:

The common carotid artery wall was imaged using a spin echo sequence acquired at four echo times (17 ms to 68 ms) in 65 participants as part of VALIDATE study. Images were acquired transverse to the artery 1.5 cm proximal to the flow divider. Mean wall thickness, mean wall signal intensity, lumen area, and outer wall area were measured for each echo. Contours were also traced on the image from the fourth echo and then propagated to the images from the preceding echoes. This was repeated using the image from the first echo. Mean wall signal intensity measurements at the four echo times were fit to a mono‐exponential decay curve to derive the mean T2 relaxation time for each set of contours.

Results:

Mean wall thickness decreased with increasing echo time, with an average thickness reduction of 8.6% between images acquired at the first and last echo times (TE) (0.93 mm at TE 17 ms versus 0.85 mm at TE 68 ms, P < 0.001). Average T2 relaxation time of the carotid wall decreased by 3% when the smaller contours from the last echo were used, which excluded the outer‐most layer (54.3 ± 7.6 ms versus 52.7 ± 6.6 ms, P = 0.03).

Conclusion:

Carotid wall thickness measurements decrease with echo time as expected by the fast T2 relaxation time of the outer‐most layer, namely the adventitia. A short echo time is needed for thickness measurements to include adventitia, which plays an important role in plaque development. J. Magn. Reson. Imaging 2013;37:1493–1498. © 2012 Wiley Periodicals, Inc.     

Accelerated 3D MERGE carotid imaging using compressed sensing with a hidden markov tree model

Purpose:

To determine the potential for accelerated 3D carotid magnetic resonance imaging (MRI) using wavelet based compressed sensing (CS) with a hidden Markov tree (HMT) model.

Materials and Methods:

We retrospectively applied HMT model‐based CS and conventional CS to 3D carotid MRI data with 0.7 mm isotropic resolution from six subjects with known carotid stenosis (12 carotids). We applied a wavelet‐tree model learned from a training database of carotid images to improve CS reconstruction. Quantitative endpoints such as lumen area, wall area, mean and maximum wall thickness, plaque calcification, and necrotic core area were measured and compared using Bland–Altman analysis along with image quality.

Results:

Rate‐4.5 acceleration with HMT model‐based CS provided image quality comparable to that of rate‐3 acceleration with conventional CS and fully sampled reference reconstructions. Morphological measurements made on rate‐4.5 HMT model‐based CS reconstructions were in good agreement with measurements made on fully sampled reference images. There was no significant bias or correlation between mean and difference of measurements when comparing rate 4.5 HMT model‐based CS with fully sampled reference images.

Conclusion:

HMT model‐based CS can potentially be used to accelerate clinical carotid MRI by a factor of 4.5 without impacting diagnostic quality or quantitative endpoints. J. Magn. Reson. Imaging 2012;36:1194–1202. © 2012 Wiley Periodicals, Inc.     

Measurement of Carotid Stenosis on Computed Tomographic Angiography: Reliability Depends on Postprocessing Technique

Purpose

We previously demonstrated the validity of axial source (AxS) image quantification of computed tomographic angiography (CTA) visualized carotid stenosis. There is concern that AxS images may not accurately measure stenosis in patients with obliquely orientated stenosis and that measurements on axial oblique (AxO) multiplanar reformats (MPR), maximum intensity projections (MIP) images, or Doppler ultrasound (DUS) are superior. We tested the performance of AxS images against AxO MPRs, MIPs, and DUS techniques for stenosis quantification.

Methods

A total of 120 consecutive patients with CTA and DUS detected carotid disease were enrolled; carotids with occlusion, near occlusion, or stenosis <40% were excluded. Proximal and distal carotid diameters and North American Symptomatic Carotid Endarterectomy Trial (NASCET) style ratios were measured independently by 2 neuroradiologists on AxS, AxO, and MIP images on separate occasions in a blinded protocol. Intra- and interobserver agreements were determined for all measurements. The performance of different image types to identify ≥70% stenosis was assessed against a NASCET-style reference standard.

Results

Intra- and interobserver reliabilities for stenosis measurements were higher for both AxS (interclass correlation coefficients [ICC], 0.87–0.93 and 0.84–0.89) and AxO images (ICCs, 0.82–0.89 and 0.86–0.92) than for MIPs (ICCs, 0.66–0.86 and 0.79–0.82), respectively. Intra- and interobserver agreements on the NASCET ratio tended to be lower than proximal stenosis measurements. AxS and AxO image proximal stenosis measurements most accurately distinguished patients with ≥70% stenosis (0.90), followed by DUS (0.83) and MIP images (0.76).

Conclusions

A single AxS image stenosis measurement was highly reproducible and accurate in the estimation of carotid stenosis, which precluded the need for AxO MPRs.     

MRI of carotid atherosclerosis to identify TIA and stroke patients who are at risk of a recurrence

Purpose:

To evaluate the potential of carotid plaque MRI to predict transient ischemic attack (TIA) and stroke recurrence in previously symptomatic patients.

Materials and Methods:

One hundred twenty‐six TIA/stroke patients with ipsilateral 30–69% carotid stenosis underwent multisequence carotid plaque MRI. The presence of a lipid‐rich necrotic core (LRNC), fibrous cap (FC) status, and intraplaque hemorrhage (IPH) were assessed. Patients were followed to determine the recurrence of ipsilateral TIA and/or stroke within 1 year after inclusion.

Results:

Thirteen patients suffered from recurrent ipsilateral clinical ischemic events (10 TIAs and 3 strokes). Carotid stenosis grade was not associated with recurrent events (hazard ratio [HR] for 50–69% versus 30–49% stenosis = 1.198; 95% confidence interval [CI], 0.383 to 3.749; P = 0.756). The presence of an LRNC (HR = 3.2001; 95% CI, 1.078 to 9.504; P = 0.036), a thin and/or ruptured FC (HR = 5.756; 95% CI, 1.913 to 17.324; P = 0.002), and IPH (HR = 3.542; 95% CI, 1.058 to 11.856; P = 0.040) were associated with recurrence.

Conclusion:

The presence of MRI‐depicted LRNC, a thin and/or ruptured FC, and IPH are associated with the recurrence of clinical cerebrovascular ischemic events in TIA and stroke patients with carotid atherosclerosis. J. Magn. Reson. Imaging 2013;37:1189–1194. © 2013 Wiley Periodicals, Inc.     

Comparison of 2D and multislab 3D magnetic resonance techniques for measuring carotid wall volumes

Purpose

To compare a multislab three‐dimensional volume‐selective fast spin‐echo (FSE) magnetic resonance (MR) sequence with a routine two‐dimensional FSE sequence for quantification of carotid wall volume.

Materials and Methods

One hundred normal subjects (50 men, mean age 44.6 years) underwent carotid vessel wall MR using 2D and 3D techniques. Carotid artery total vessel volume, lumen volume, wall volume, and wall/outer wall (W/OW) ratio were measured over 20 contiguous slices. Two‐ (2D) and three‐dimensional (3D) results were compared.

Results

The mean difference between 2D and 3D datasets (as a percentage of the mean absolute value) was 1.7% for vessel volume, 4.9% for lumen volume, 4.7% for wall volume, and 5.8% for W/OW ratio. There was good correlation between 2D and 3D models for total vessel volume (R² = 0.93, P < 0.001), lumen area (R² = 0.92, P < 0.001), and wall volume (R² = 0.77, P < 0.001). The correlation for the W/OW ratio was weaker (R² = 0.30; P < 0.001). The signal‐to‐noise ratio (SNR) for the 3D technique was 2.1‐fold greater than for the 2D technique (P < 0.001). When using the 3D sequence, scan time was reduced by 63%.

Conclusion

Multislab volume selective 3D FSE carotid arterial wall imaging performs similarly to a conventional 2D technique, but with over twice the SNR and substantially reduced scan time. J. Magn. Reson. Imaging 2008;28:1476–1482. © 2008 Wiley‐Liss, Inc.