Repeatability, robustness, and reproducibility of texture features on 3 Tesla liver MRI.

OBJECTIVE: Texture features are proposed for classification and prognostication, with lacking information about variability. We assessed 3 T liver MRI feature variability. METHODS: Five volunteers underwent standard 3 T MRI, and repeated with identical and altered parameters. Two readers placed regions of interest using 3DSlicer. Repeatability (between standard and repeat scan), robustness (between standard and parameter changed scan), and reproducibility (two reader variation) were computed using coefficient of variation (CV). RESULTS: 67%, 49%, and 61% of features had good-to-excellent (CV ≤ 10%) repeatability on ADC, T1, and T2, respectively, least frequently for first order (19-35%). 22%, 19%, and 21% of features had good-to-excellent robustness on ADC, T1, and T2, respectively. 52%, 35%, and 25% of feature measurements had good-to-excellent inter-reader reproducibility on ADC, T1, and T2, respectively, with highest good-to-excellent reproducibility for first order features on ADC/T1. CONCLUSION: We demonstrated large variations in texture features on 3 T liver MRI. Further study should evaluate methods to reduce variability.

Accelerated Internal Auditory Canal Screening Magnetic Resonance Imaging Protocol With Compressed Sensing 3-Dimensional T2-Weighted Sequence.

BACKGROUND AND PURPOSE: High-resolution T2-weighted sequences are frequently used in magnetic resonance imaging (MRI) studies to assess the cerebellopontine angle and internal auditory canal (IAC) in sensorineural hearing loss patients but have low yield and lengthened examinations. Because image content in the Wavelet domain is sparse, compressed sensing (CS) that uses incoherent undersampling of k-space and iterative reconstruction can accelerate MRI acquisitions. We hypothesized that an accelerated CS T2 Sampling Perfection with Application optimized Contrasts using different flip angle Evolution (SPACE) sequence would produce acceptable diagnostic quality for IAC screening protocols. MATERIAL AND METHODS: Seventy-six patients underwent 3 T MRI using conventional SPACE and a CS T2 SPACE prototype sequence for screening the IACs were identified retrospectively. Unilateral reconstructions for each sequence were separated, then placed into mixed folders for independent, blinded review by 3 neuroradiologists during 2 sessions 4 weeks apart. Radiologists reported if a lesion was present. Motion and visualization of specific structures were rated using ordinal scales. McNemar, Wilcoxon, Cohen κ, and Mann-Whitney U tests were performed for accuracy, equivalence, and interrater and intrarater reliability. RESULTS: T2 SPACE using CS reconstruction reduced scan time by 80% to 50 seconds and provided 98.7% accuracy for IAC mass detection by 3 raters. Radiologists preferred conventional images (0.7-1.0 reduction on 5-point scale, P < 0.001), but rated CS SPACE acceptable. The 95% confidence for reduction in any cerebellopontine angle, IAC, or fluid-filled inner ear structure assessment with CS SPACE did not exceed 0.5. CONCLUSIONS: Internal auditory canal screening MRI protocols can be performed using a 5-fold accelerated T2 SPACE sequence with compressed sensing while preserving diagnostic image quality and acceptable lesion detection rate.

Does the Addition of DWI to Fluid-Sensitive Conventional MRI of the Sacroiliac Joints Improve the Diagnosis of Sacroiliitis?

OBJECTIVE: The purpose of this study was to determine whether adding DWI to conventional MRI of the sacroiliac joints improves the diagnostic performance of MRI readers in the detection of sacroiliitis. MATERIALS AND METHODS: MR images of the sacroiliac joints of 63 patients with lower back pain obtained between January 2016 and December 2016 were analyzed retrospectively. Three readers reviewed the MRI studies for bone marrow edema lesions around the sacroiliac joints as a marker of active sacroiliitis and gave a diagnostic confidence score of 0-4 using MRI without DWI and MRI with DWI in separate sessions. The normalized apparent diffusion coefficient mean (nADCmean) was measured. Clinical and radiologic data using the Assessment of Spondyloarthritis International Society criteria were the reference for the diagnosis of sacroiliitis. Diagnostic performance, confidence scores, and interreader agreement for the MRI methods were compared. The nADCmean values of patients with and those without sacroiliitis were compared. RESULTS: The accuracy, sensitivity, and specificity of MRI without DWI were 68.3%, 69.0%, and 67.6% and for MRI with DWI were 74.6%, 69.0%, and 79.4% (accuracy and sensitivity, p > 0.100; specificity, p = 0.039). The mean confidence score for MRI without DWI was 3.60 and for MRI with DWI was 3.67 (p = 0.270). The kappa coefficient for MRI without DWI was 0.28 and for MRI with DWI was 0.46 (p = 0.041). The nADCmean in patients with sacroiliitis was 3.86 and in patients without sacroiliitis was 1.6 (p ≤ 0.001). The nADCmean AUC was 0.758 (95% CI, 0.67-0.83). CONCLUSION: The addition of DWI to conventional MRI does not significantly improve overall diagnostic performance in terms of accuracy, sensitivity, or confidence in the detection of inflammatory sacroiliitis, but it does have increased specificity and interobserver agreement. ADC threshold values can be used as predictors of sacroiliitis but give no added advantage over MRI with DWI.

Advanced MRI of the Optic Nerve.

BACKGROUND: Clinical orbital MRI protocols are routinely used to study the optic nerves and exclude compressive lesions, infarctions, or inflammation. However, the small caliber and divergent oblique orientations of the optic nerves make it challenging to characterize them well with conventional MRI, especially since adjacent air-filled bony structures distort the MRI signal and motion is a problem even in cooperative, healthy volunteers. EVIDENCE ACQUISITION: Over the past 3 years we have experimented with multiple novel MRI approaches and sequences to better characterize the optic nerves. The perfect MRI protocol would be quantitative and sensitive to subtle optic nerve pathologic changes, provide high spatial resolution, be rapidly acquired, and resistant to motion degradation. RESULTS: This review provides an update of recent MRI sequence innovations for the optic nerves being currently translated into clinical practice. Methods discussed include rapid MRI with compressed sensing or simultaneous multislice approaches, postprocessing techniques for quantitative T2 mapping or track density imaging, and multiple MRI sequences for measuring diffusion in the optic nerves. CONCLUSIONS: Recently-developed orbit-specific MRI coils, quantitative sequences, and rapid acquisition techniques can improve our future ability to study optic nerve pathologies noninvasively. As advanced MRI becomes more proficient at characterizing the optic nerves, its role in the clinical management of patients should increase.

Three-dimensional MR Cholangiopancreatography in a Breath Hold with Sparsity-based Reconstruction of Highly Undersampled Data.

Purpose To develop a three-dimensional breath-hold (BH) magnetic resonance (MR) cholangiopancreatographic protocol with sampling perfection with application-optimized contrast using different flip-angle evolutions (SPACE) acquisition and sparsity-based iterative reconstruction (SPARSE) of prospectively sampled 5% k-space data and to compare the results with conventional respiratory-triggered (RT) acquisition. Materials and Methods This HIPAA-compliant prospective study was institutional review board approved. Twenty-nine patients underwent conventional RT SPACE and BH-accelerated SPACE acquisition with 5% k-space sampling at 3 T. Spatial resolution and other parameters were matched when possible. BH SPACE images were reconstructed by enforcing joint multicoil sparsity in the wavelet domain (SPARSE-SPACE). Two board-certified radiologists independently evaluated BH SPARSE-SPACE and RT SPACE images for image quality parameters in the pancreatic duct and common bile duct by using a five-point scale. The Wilcoxon signed-rank test was used to compare BH SPARSE-SPACE and RT SPACE images. Results Acquisition time for BH SPARSE-SPACE was 20 seconds, which was significantly (P < .001) shorter than that for RT SPACE (mean ± standard deviation, 338.8 sec ± 69.1). Overall image quality scores were higher for BH SPARSE-SPACE than for RT SPACE images for both readers for the proximal, middle, and distal pancreatic duct, but the difference was not statistically significant (P > .05). For reader 1, distal common bile duct scores were significantly higher with BH SPARSE-SPACE acquisition (P = .036). More patients had acceptable or better overall image quality (scores ≥ 3) with BH SPARSE-SPACE than with RT SPACE acquisition, respectively, for the proximal (23 of 29 [79%] vs 22 of 29 [76%]), middle (22 of 29 [76%] vs 18 of 29 [62%]), and distal (20 of 29 [69%] vs 13 of 29 [45%]) pancreatic duct and the proximal (25 of 28 [89%] vs 22 of 28 [79%]) and distal (25 of 28 [89%] vs 24 of 28 [86%]) common bile duct. Conclusion BH SPARSE-SPACE showed similar or superior image quality for the pancreatic and common duct compared with that of RT SPACE despite 17-fold shorter acquisition time. (©) RSNA, 2016.

Contrast-enhanced radial 3D fat-suppressed T1-weighted gradient-recalled echo sequence versus conventional fat-suppressed contrast-enhanced T1-weighted studies of the head and neck.

OBJECTIVE: Traditional fat-suppressed T1-weighted spin-echo or turbo spin-echo (TSE) sequences (T1-weighted images) may be degraded by motion and pulsation artifacts in head-and-neck studies. Our purpose is to evaluate the role of a fat-suppressed T1-weighted 3D radial gradient-recalled echo sequence (radial-volumetric interpolated breath-hold examination [VIBE]) in the head and neck as compared with standard contrast-enhanced fat-suppressed T1-weighted images. MATERIALS AND METHODS: We retrospectively evaluated 21 patients (age range, 9-67 years) who underwent head-and-neck MRI at 1.5 T. Both contrast-enhanced radial-VIBE and conventional fat-suppressed TSE contrast-enhanced T1-weighted imaging were performed. Two radiologists evaluated multiple parameters of image quality, graded on a 5-point scale. Mixed-model analysis of variance and interobserver variability assessment were performed. RESULTS: The following parameters were scored as significantly better for the contrast-enhanced radial-VIBE sequence than for conventional contrast-enhanced T1-weighted imaging: overall image quality (p < 0.0001), degree of fat suppression (p = 0.006), mucosal enhancement (p = 0.004), muscle edge clarity (p = 0.049), vessel clarity (p < 0.0001), respiratory motion artifact (p = 0.002), pulsation artifact (p < 0.0001), and lesion edge sharpness (p = 0.004). Interobserver agreement in qualitative evaluation of the two sequences showed fair-to-good agreement for the following variables: overall image quality (intraclass correlation coefficient [ICC], 0.779), degree of fat suppression (ICC, 0.716), mucosal enhancement (ICC, 0.693), muscle edge clarity (ICC, 0.675), respiratory motion artifact (ICC, 0.516), lesion enhancement (ICC, 0.410), and lesion edge sharpness (ICC, 0.538). Excellent agreement was shown for vessel clarity (ICC, 0.846) and pulsation artifact (ICC, 0.808). CONCLUSION: The radial-VIBE sequence is a viable motion-robust improvement on the conventional fat-suppressed T1-weighted sequence.

Quadruple inversion-recovery b-SSFP MRA of the abdomen: initial clinical validation.

The purpose of this study is to assess the image quality and diagnostic accuracy of non-contrast quadruple inversion-recovery balanced-SSFP MRA (QIR MRA) for detection of aortoiliac disease in a clinical population. QIR MRA was performed in 26 patients referred for routine clinical gadolinium-enhanced MRA (Gd-MRA) for known or suspected aortoiliac disease. Non-contrast images were independently evaluated for image quality and degree of stenosis by two radiologists, using consensus Gd-MRA as the reference standard. Hemodynamically significant stenosis (≥50%) was found in 10% (22/226) of all evaluable segments on Gd-MRA. The sensitivity and specificity for stenosis evaluation by QIR MRA for the two readers were 86%/86% and 95%/93% respectively. Negative predictive value and positive predictive value were 98%/98% and 63%/53% respectively. For stenosis evaluation of the aortoiliac region QIR MRA showed good agreement with the reference standard with high negative predictive value and a tendency to overestimate mild disease presumably due to the flow-dependence of the technique. QIR MRA could be a reasonable alternative to Gd-MRA for ruling out stenosis when contrast is contraindicated due to impaired kidney function or in patients who undergo abdominal MRA for screening purposes. Further work is necessary to improve performance and justify routine clinical use.

Dynamic contrast-enhanced magnetic resonance imaging measurement of renal function in patients undergoing partial nephrectomy: preliminary experience.

OBJECTIVES: To evaluate changes in single-kidney glomerular filtration rate (SK-GFR) using low-dose dynamic contrast-enhanced magnetic resonance (MR) renography (MRR) in patients undergoing partial nephrectomy for renal masses. MATERIALS AND METHODS: In this Health Information Patient Protection Act-compliant prospective study, 18 patients with renal masses underwent preoperative MR imaging at 1.5 T for renal mass evaluation and low-dose gadolinium-enhanced MRR. Magnetic resonance renography was repeated approximately 48 to 72 hours and 6 months after partial nephrectomy. Single-kidney glomerular filtration rate was calculated from the MRR images, and the right and left kidney values were summed for total MR-GFR. Postoperative changes in SK-GFR and MR-GFR were compared with changes in estimated glomerular filtration rate calculated using modification of diet in renal disease formula, renal lesion characteristics, ischemia type (warm vs cold), and ischemia time. RESULTS: A decrease in the operated kidney SK-GFR was seen in 15 of the 18 patients, with a mean (SD) loss of 31% (23%), whereas estimated glomerular filtration rate decreased in 13 of the 18 patients with mean (SD) decrease of 19% (14%). Decrease in SK-GFR was greatest in the patients with warm ischemia time greater than 40 minutes and least in the patients with cold ischemia. In the immediate postoperative period, 6 of 7 patients (86%) with preoperative MR-GFR less than 60 mL/min per 1.73 m failed to demonstrate compensatory increase in SK-GFR in the nonoperated kidney, whereas 5 of 11 patients with baseline MR-GFR more than 60 mL/min per 1.73 m showed compensatory increase in nonoperated kidney SK-GFR. CONCLUSIONS: Magnetic resonance renography can demonstrate functional loss in the operated kidney and compensatory increase in the function of the contralateral kidney, thus enabling evaluation of various surgical techniques on kidney function.

Highly accelerated single breath-hold noncontrast thoracic MRA: evaluation in a clinical population.

OBJECTIVES: The objective of this study was to evaluate the performance of a highly accelerated breath-hold 3-dimensional noncontrast-enhanced steady-state free precession thoracic magnetic resonance angiography (NC-MRA) technique in a clinical population, including assessment of image quality, aortic dimensions, and aortic pathology, compared with electrocardiographically gated gadolinium-enhanced MRA (Gd-MRA). MATERIALS AND METHODS: After approval from the institution board and informed consent were obtained, 30 patients (22 men; mean age, 53.4 years) with known or suspected aortic pathology were imaged with NC-MRA followed by Gd-MRA at a single examination at 1.5 T. Images were made anonymous and reviewed by 2 readers for aortic pathology and diagnostic confidence on a 5-point scale (1, worst; 5, best) on a patient basis. Image quality and artifacts were also evaluated in 10 vascular segments: aortic annulus, sinuses of Valsalva, sinotubular junction, ascending aorta, aortic arch, descending aorta, diaphragmatic aorta, great vessel origins, and the left main and right coronary artery origins. Finally, aortic dimensions were measured in each of the 7 aortic segments. The Wilcoxon signed rank test was used to compare diagnostic confidence, image quality, and artifact scores between NC-MRA and Gd-MRA. The paired Student t test and Bland-Altman analysis were used for comparison of aortic dimensions. RESULTS: All patients completed NC-MRA and Gd-MRA successfully. Vascular pathologic findings were concordant with Gd-MRA in 29 of 30 (96.7%) patients and 28 of 30 (93.3%) patients for readers 1 and 2, respectively, with high diagnostic confidence (mean [SD], 4.35 [0.77]) not significantly different from Gd-MRA (4.38 [0.64]; P = 0.74). The image quality and artifact scores were comparable with Gd-MRA in most vascular segments. Notable differences were observed at the ascending aorta, where Gd-MRA had superior image quality (4.13 [0.73]) compared with NC-MRA (3.80 [0.88]; P = 0.028), and at the coronary artery origins where NC-MRA was considered superior (NC-MRA vs Gd-MRA, 3.38 [1.47] vs 2.78 [1.21] for the left main artery and NC-MRA vs Gd-MRA, 3.55 [1.40] vs 2.32 [1.16] for the right coronary artery; P < 0.05, both comparisons). The aortic dimensions were comparable, with the only significant difference observed at the ascending aorta, where NC-MRA dimension (4.05 [0.76]) was less than 1 mm smaller than that of Gd-MRA (4.12 [0.7]; P = 0.043). CONCLUSIONS: Breath-hold NC-MRA of the thoracic aorta yields good image quality, comparable to Gd-MRA, with high accuracy for aortic dimension and pathology. It can be considered as an alternative to Gd-MRA in patients with relative contraindications to gadolinium contrast or problems with intravenous access.