Identification of peroneal artery perforators using non-contrast-enhanced T2prep multi-shot gradient echo planar imaging MRA.

The purpose of this study was to investigate the spatial resolution of non-contrast-enhanced (CE) T2prep multi-shot gradient echo planar imaging (MSG-EPI) magnetic resonance angiography (MRA) required to identify peroneal artery perforators and demonstrate its effectiveness in preoperative simulation. Twenty-six legs of 13 volunteers were scanned using non-CE T2prep MSG-EPI-MRA at three spatial resolutions: 1.0-, 0.8-, and 0.6-mm isotropic voxels. The location and number of peroneal artery perforators that could be candidates for free fibula flaps were identified by consensus among three plastic surgeons. Surgeons distinguished between septocutaneous and musculocutaneous perforators using MRA, and confirmed the accuracy of their presence and identification using ultrasonography (US). The ability to detect hypoplasia or stenosis of the anterior tibial, posterior tibial, and peroneal arteries was evaluated by confirming the consistency between the MRA and US results. The number of cutaneous perforators identified using MRA and confirmed using US was 39, 51, and 52 at each respective resolution. The discrimination accuracies between septocutaneous and musculocutaneous perforators were 92.3%, 96.1%, and 96.2%. The number of identified septocutaneous perforators was 1.3 ± 0.6, 1.6 ± 0.8, and 1.7 ± 0.8 at 1.0-, 0.8-, and 0.6-mm data, respectively. All the MRA results, including hypoplasia and stenosis, were consistent with the US results. Non-CE T2prep MSG-EPI-MRA with a spatial resolution of 0.8 mm or less shows promise for identifying septocutaneous perforators of the peroneal artery, suggesting its potential as an alternative to conventional imaging methods for the preoperative planning of free fibula osteocutaneous flap transfers.

Robustness of a Combined Modified Dixon and PROPELLER Sequence with Two Interleaved Echoes in Clinical Head and Neck MRI.

PURPOSE: The combination of modified Dixon (mDixon) and periodically rotated overlapping parallel lines with enhanced reconstruction sequence with two interleaved echoes, which promotes uniform fat-suppression and motion insensitivity, has recently become available for commercial magnetic resonance imaging (MRI) scanners. To compare the robustness of this combination sequence with that of standard Cartesian mDixon sequence for fat-suppressed T2-weighted imaging in clinical head and neck MRI. METHODS: Fifty patients with head and neck tumors were involved this study. All patients underwent MRI using both the combination and standard sequences. Two radiologists independently scored motion artifacts and water-fat separation error using a 4-point scale (1, unacceptable; 4, excellent). Furthermore, comprehensive comparative evaluation was performed using a 5-point scale (1, substantially inferior; 5, substantially superior). Data were statistically analyzed using the Wilcoxon signed-rank test. RESULTS: In the motion artifact assessment, ratings of 3 or 4 points were assigned to 45% (observer-1, 58.0%; observer-2, 32.0%) and 97% (100%; 94.0%) of images for the standard and combination sequences, respectively (P < 0.001). For the water-fat separation error assessment, ratings of 3 or 4 points were assigned to 100% (100%; 100%) and 85% (84.0%; 86.0%) of images, respectively (P < 0.001). In the comprehensive evaluation, of the 100 cases (observer-1, 50; observer-2, 50), 96 were rated at four or five points. In cases with slight or no motion artifacts and water-fat separation errors, the combination sequence was superior to the standard sequence in term of noise and sharpness, and equal in terms of contrast. CONCLUSION: Although water-fat separation errors increased significantly in the combination sequence, most of these were acceptable. The significantly decreased motion artifacts in the combination sequence significantly improved image quality overall.

Combined modified-Dixon and PROPELLER method with low refocusing flip angle for contrast-enhanced fat-suppressed T1-weighted MRI: A prospective cross-sectional study.

PURPOSE: To propose the combined modified-Dixon and PROPELLER sequence with low refocusing flip angle (RFA) and investigate whether this sequence can acquire clinical contrast-enhanced (CE), fat-suppressed T1-weighted (T1W) images of the head and neck. METHODS: The optimal RFA for T1W imaging was investigated in the brain of a healthy volunteer. The motion artifacts, water-fat separation error, contrast ratio (CR), and comprehensive quality were evaluated through comparison with a standard Cartesian modified-Dixon sequence in 50 patients. Two radiologists independently scored motion artifacts and water-fat separation error using a 4-point scale (1, unacceptable; 4, excellent) and comprehensive quality using a 5-point scale (1, substantially inferior; 5, substantially superior). The CR between CE lesions and non-CE muscle was calculated. RESULTS: The optimal RFA of 40° was determined. In the motion artifact assessment, ratings of 3 or 4 points were assigned to 83% (observer-1, 42/50; observer-2, 41/50) and 99% (50/50; 49/50) of cases for the standard and proposed sequences, respectively (p < 0.001; p < 0.001). For the water-fat separation error assessment, ratings of 3 or 4 points were assigned to 100% (50/50; 50/50) and 97% (48/50; 49/50) of cases, respectively (p < 0.001; p = 0.02). In comprehensive evaluation, the proposed sequence was equal, slightly superior, or substantially superior to the standard sequence in 85% (39/50; 46/50). The CR was significantly higher with the proposed sequence [2.27 (1.99-2.97) vs. 2.08 (1.88-2.42), p < 0.001]. CONCLUSION: The proposed sequence acquired stable fat-suppressed CE T1W images without motion artifacts and yielded superior overall image quality compared with the standard sequence.

Simultaneous Visualization of Vessels and Brain Tumor with Contrast-enhanced Three-dimensional Phase-contrast MR Imaging.

The sequence for concurrently depicting engulfed vessels and a well-enhanced tumor in once-off scanning has never been reported for preoperative magnetic resonance imaging for brain tumor resection. Multimodal fusion techniques have been recently developed, but the risks of misregistration still remain. Here a case is reported where contrast-enhanced three-dimensional phase contrast sequence concurrently depicted an engulfed vessel and metastatic brain tumor in once-off scanning and related technical aspects are discussed.

Usefulness of non-contrast-enhanced MRI with two-dimensional balanced steady-state free precession for the acquisition of the pulmonary venous and left atrial anatomy pre catheter ablation of atrial fibrillation: Comparison with contrast enhanced CT in clinical cases.

BACKGROUND: To investigate the feasibility of substituting non-contrast-enhanced MR (non-CE-MR) imaging with a two-dimensional (2D) balanced steady-state free precession (b-SSFP) sequence for contrast-enhanced computed tomography (CE-CT) for atrial fibrillation (AF) ablation. METHODS: Fifty-four patients that underwent AF ablation under the guidance of a 3D electro-anatomical mapping system with CE-CT (n = 27) or non-CE-MR images (n = 27) were studied. Procedural results were compared between the two groups. Furthermore, in 22 patients who underwent both CE-CT and non-CE-MRI, two cardiologists independently scored the multiplanar reformatted images on a scale of 1 to 4 (from 1, poor, to 4, excellent). RESULTS: The image score was nearly 0.5 point higher with the CE-CT method. However, the procedural results such as the surface registration error (1.0 [0.8-1.6] mm versus 1.0 [0.8-1.35] mm, P = 0.88) and procedure time (185 [159-199] min versus 185 [142-221] min, P = 0.86) did not significantly differ between the CE-CT and non-CE-MR groups. CONCLUSION: The non-CE-MR method with a 2D-b-SSFP sequence can give us adequate information on AF ablation without any radiation exposure or contrast medium usage

Visualizing radiofrequency lesions using delayed-enhancement magnetic resonance imaging in patients with atrial fibrillation: A modification of the method used by the University of Utah group.

BACKGROUND: Atrial tissue fibrosis has previously been identified using delayed-enhancement MRI (DE-MRI) in patients with atrial fibrillation (AF). Although the clinical importance of DE-MRI is well recognized, the visualization of atrial fibrosis and radiofrequency (RF) lesions has still not been achieved in Japan, primarily because of the differences in contrast agents, volume-rendering tools, and technical experience. The objective of this study was to visualize RF lesions by using commercially available tools. METHODS: DE-MRI was performed in 15 patients who had undergone AF ablation (age, 59±4 years, left atrium diameter, 40±2 mm). Specific parameters for MR scanning obtained from previous reports were modified. RESULTS: Of the 15 images, the images of three patients were uninterpretable owing to low image quality. RF lesions could be visualized in 8 (67%) of the 12 patients. CONCLUSIONS: In the current study, we successfully demonstrated that RF lesions could be visualized in Japanese patients using DE-MRI, although only commercially available tools were used.

Visualization of the radiofrequency lesion after pulmonary vein isolation using delayed enhancement magnetic resonance imaging fused with magnetic resonance angiography.

BACKGROUND: The radiofrequency (RF) lesions for atrial fibrillation (AF) ablation can be visualized by delayed enhancement magnetic resonance imaging (DE-MRI). However, the quality of anatomical information provided by DE-MRI is not adequate due to its spatial resolution. In contrast, magnetic resonance angiography (MRA) provides similar information regarding the left atrium (LA) and pulmonary veins (PVs) as computed tomography angiography. We hypothesized that DE-MRI fused with MRA will compensate for the inadequate image quality provided by DE-MRI. METHODS: DE-MRI and MRA were performed in 18 patients who underwent AF ablation (age, 60±9 years; LA diameter, 42±6 mm). Two observers independently assessed the DE-MRI and DE-MRI fused with MRA for visualization of the RF lesion (score 0-2; where 0: not visualized and 2: excellent in all 14 segments of the circular RF lesion). RESULTS: DE-MRI fused with MRA was successfully performed in all patients. The image quality score was significantly higher in DE-MRI fused with MRA compared to DE-MRI alone (observer 1: 22 (18, 25) vs 28 (28, 28), p<0.001; observer 2: 24 (23, 25) vs 28 (28, 28), p<0.001). CONCLUSIONS: DE-MRI fused with MRA was superior to DE-MRI for visualization of the RF lesion owing to the precise information on LA and PV anatomy provided by DE-MRI.

Acquisition of the pulmonary venous and left atrial anatomy with non-contrast-enhanced MRI for catheter ablation of atrial fibrillation: Usefulness of two-dimensional balanced steady-state free precession.

BACKGROUND: Usually, the pulmonary venous and left atrial (PV-LA) anatomy is assessed with contrast-enhanced computed tomographic imaging for catheter ablation of atrial fibrillation (AF). A non-contrast-enhanced magnetic resonance (MR) imaging method has not been established. Three-dimensional balanced steady-state free precession (3D b-SSFP) sequences cannot visualize the PV-LA anatomy simultaneously because of the signal intensity defect of pulmonary veins. We compared two-dimensional (2D) b-SSFP sequences with 3D b-SSFP sequences in depicting the PV-LA anatomy with non-contrast-enhanced MR imaging for AF ablation. METHODS: Eleven healthy volunteers underwent non-contrast-enhanced MR imaging with 3D b-SSFP and 2D b-SSFP sequences. The MR images were reconstructed on the 3D PV-LA surface image. Two experienced radiological technicians independently scored the multiplanar reformatted (MPR) images on a scale of 1-4 (from 1, not visualized, to 4, excellent definition). The overall score was a sum of 5 segments (LA and 4 PVs). RESULTS: In the 2D b-SSFP method, MR imaging was successfully performed, and the 3D PV-LA surface image was precisely reconstructed in all healthy volunteers. The image score was significantly higher in the 2D b-SSFP method compared to the 3D b-SSFP method (19 [19; 20] vs. 12 [11; 15], p=0.004, for both observers). No PV signal intensity defects occurred in the 2D b-SSFP method. CONCLUSIONS: The 2D b-SSFP sequence was more useful than the 3D b-SSFP sequence in adequately depicting the PV-LA anatomy.

Fusion of Delayed-enhancement MR Imaging and Contrast-enhanced MR Angiography to Visualize Radiofrequency Ablation Scar on the Pulmonary Vein.

Delayed-enhancement magnetic resonance imaging (DE-MRI) is reported to detect the radiofrequency (RF) ablation scar of pulmonary vein isolation. However, the precise localization of RF scar is difficult to recognize due to the poor anatomical information of the 3-dimensionally reconstructed DE-MRI. We report 2 cases in which fusion of DE-MRI and contrast-enhanced MR angiography facilitated the identification of RF scar, and we detail our fusion method.