Borisch, Eric A.

ABSTRACT Background Clinical T 2 ‐weighted (T2W) MRI of prostate cancer (PCa) usually implements a 2D fast‐spin‐echo (FSE) sequence, but understanding the echo‐time‐dependent contrast behavior is not straightforward due to the complicated FSE signal evolution. Consequently, consensus‐based recommendations on the optimal effective echo time (TE eff ) to maximize contrast are lacking. Purpose To investigate the effect of TE eff on PCa lesion contrast in prostate T2W MRI. Study Type Phantom and in vivo prospective study. Subjects A standard MRI phantom and 53 prostate cancer patients (29 for image evaluation and 24 for quantitative lesion analysis). Field Strength and Sequence Multi‐slice T2W FSE sequence at 3 T acquired at multiple TE eff values. Assessment Three readers (13, 25, and 27 years' experience) evaluated TE eff = 100 ms versus 150 ms on diagnostic quality and reader preference. The effective T 2 relaxation rates ( T 2,eff ) were measured using FSE sequences in the phantom and used to predict the optimal TE eff maximizing T2W contrasts. From multi‐TE eff scans of subjects with suspected PCa, T 2,eff values of PCa lesions and healthy tissue were measured and used to calculate the optimal TE eff maximizing the lesion contrast. In vivo contrast metrics were measured as a function of TE eff . Statistical Tests Wilcoxon test of reader scores, with p < 0.05 defining statistical significance. Results No statistically significant difference was found in diagnostic quality between TE eff = 150 ms and 100 ms images, but all three readers significantly favored TE eff = 150 ms. Phantom experiments demonstrated that TE eff ‐dependent FSE signal progression can be characterized by T 2,eff values typically 40% longer than actual T 2 values, allowing accurate prediction of optimal TE eff within 2%–5%. Applied to PCa imaging, in vivo measurements indicated that effective T 2 relaxation times of the prostate are on average 1.5× longer than published T 2 values. Data Conclusion The benefits of TE eff = 150 ms versus 100 ms in prostate T2W FSE were supported by reader preference, phantom experiments, in vivo measurements, and analytic optimizations. Evidence Level 2. Technical Efficacy 2.

Abstract Purpose To evaluate the effectiveness of subcutaneous glucagon in reducing motion artifact during prostate MRI through intraindividual comparison. Methods At our institution patients undergoing a clinical prostate MRI exam receive 1 mg of subcutaneous glucagon before scanning. From February 15, 2024 to February 11, 2025 33 such patients were recruited to undergo an additional, research exam without glucagon. All exams were acquired at 3T. An axial T2-weighted spin-echo series (T2-WI) was acquired within both exams. Evaluation of the T2-WI series was done by three experienced radiologists using the criteria of diagnostic quality (0–3 scale), PI-QUALv2 (0–3 sum), motion artifact (significant, visible, none), and reviewer preference (five-point relative scale). Due to differences in prescribed coverage, the scan times for the two T2-WI sequences were in general different for each subject. Results were stratified using the acquisition time ratio (Trel) between the glucagon vs. non-glucagon scans. Wilcoxon tests assessed score differences. Results Across all 33 subjects, no significant differences were found between glucagon and non-glucagon scans. However, the observed negative correlation between glucagon preference and Trel (p = 0.026) led to stratification into low-Trel (n = 16) and high-Trel (n = 17) groups. In the low-Trel group the glucagon scans provided significantly improved diagnostic quality (p = 0.048), PI-QUALv2 sum (p = 0.049), motion scores (p = 0.047), and reader preference (p = 0.042). Conclusion Subcutaneous glucagon provides improved image quality in prostate T2-WI MRI when scan duration remains within 1.25× of that of a non-glucagon T2-WI series. The benefit appears to decrease with longer scan times.

AbstractPurposeTo study if adaptive image receive (AIR) receiver coil elements can be configured into a 2D array with high (>45% by diameter) element‐to‐element overlap, allowing improved SNR at depth (0.7–1.5× element diameter) versus conventional (20%) overlap.MethodsAn anterior array composed of twenty 10‐cm diameter elements with 45% overlap arranged into a 4 × 5 grid and a similar 3 × 7 twenty‐one‐element posterior array were constructed. SNR and g‐factor were measured in a pelvic phantom using the new high‐density (HD) arrays (41 total elements) and compared to vendor AIR‐based arrays (30 total elements) with conventional overlap. T2‐weighted fast‐spin‐echo (T2SE) images acquired using both arrays were compared in 20 subjects. SNR was estimated in vivo. Results were compared blindly by three uroradiologists using a five‐point scale. Images using the HD arrays were also compared to a set of images acquired over a range of acceleration factors (R = 2.0, 2.5, 3.0) with the conventional arrays.ResultsSNR within the phantom was on average 15% higher for R = 1.0, 1.5, and 2.0 using the HD arrays. Across the 20 subjects SNR within the prostate was 11% higher and assessed radiologically as significantly higher (p < 0.001) for the HD versus conventional arrays. At all acceleration factors the new HD arrays outperformed the conventional arrays (p ≤ 0.01), allowing increased R for similar SNR.ConclusionAIR elements can be configured into 2D arrays with high (45%) element‐to‐element overlap, consistently providing increased SNR at depth versus arrays with conventional (20%) overlap. The SNR improvement allows increased acceleration in T2SE prostate MRI.

PurposeThe purpose is to develop a model‐based image‐reconstruction method using wavelet sparsity regularization for maintaining restoration of through‐plane resolution but with improved retention of SNR versus linear reconstruction using Tikhonov (TK) regularization in high through‐plane resolution (1 mm) T2‐weighted spin‐echo (T2SE) images of the prostate.MethodsA wavelet sparsity (WS)–regularized image reconstruction was developed that takes as input a set of ≈80 overlapped 3‐mm‐thick slices acquired using a T2SE multislice scan and typically 30 coil elements. After testing in contrast and resolution phantoms and calibration in 6 subjects, the WS reconstruction was evaluated in 16 consecutive prostate T2SE MRI exams. Results reconstructed with nominal 1‐mm thickness were compared with those from the TK reconstruction with the same raw data. Results were evaluated radiologically. The ratio of magnitude of prostate signal to periprostatic muscle signal was used to assess the presence of noise reduction. Technical performance was also compared with a commercial 3D‐T2SE sequence.ResultsThe new WS reconstruction was assessed as superior statistically to TK for overall SNR, contrast, and multiple evaluation criteria related to sharpness while retaining the high (1 mm) through‐plane resolution. Wavelet sparsity tended to provide improved overall diagnostic quality versus TK, but not significantly so. In all 16 studies, the prostate‐to‐muscle signal ratio increased.ConclusionsModel‐based WS‐regularized reconstruction consistently provides improved SNR in high (1 mm) through‐plane resolution images of prostate T2SE MRI versus linear reconstruction using TK regularization.

PurposeThe purpose is to develop a retrospective correction for subtle slice‐to‐slice positional inconsistencies that can occur when overlapped slices are acquired for super resolution in T2‐weighted spin‐echo multislice imaging.MethodsSpin‐echo acquisition of overlapped slices is typically done using multiple passes. After the passes are assembled into the final slice set, consecutive slices are correlated due to their overlap. Cross correlation was used to measure slice‐to‐slice displacement. After Z‐dependent filtering to preserve true object shape, the displacements were used to correct slice position. The method was tested in a phantom moved slowly (0.16‐0.63 mm/pass) under computer control and in vivo in 16 patients having prostate MRI.ResultsOver the motion range, the correlation method had an accuracy within 0.03 mm/pass and precision ± 0.20 mm (ie, subpixel). Corrected images visually resemble the true object. Over the patient studies, the mean range of motion in the anterior–posterior direction was 1.63 mm. Motion‐corrected axial images and the sagittal reformats were evaluated as significantly superior over those formed without motion correction.ConclusionThe retrospective correlation‐based motion‐correction method provides significant improvement in the slice‐to‐slice registration necessary for effective super resolution using overlapped slices.

PurposeTo reduce slice‐to‐slice motion effects in multislice ‐weighted fast‐spin‐echo ( FSE) imaging, manifest as “scalloping” in reformats, by modification of the acquisition strategy and to show applicability in prostate MRI.Methods FSE images of contiguous or overlapping slices are typically acquired using multiple passes in which each pass is comprised of multiple slices with slice‐to‐slice gaps. Combination of slices from all passes provides the desired sampling. For enhancement of through‐plane resolution with super resolution or for reformatting into other orientations, subtle ≈1 mm motion between passes can cause objectionable “scalloping” artifact. Here we address this by subdivision of each pass into multiple segments. Interleaving of segments from the multiple passes causes all slices to be acquired over substantially the same time, reducing pass‐to‐pass motion effects. This was implemented in acquiring 78 overlapped FSE axial slices and studied in phantoms and in 14 prostate MRI patients. Super‐resolution axial images and sagittal reformats from the original and new segmented acquisitions were evaluated by 3 uroradiologists.ResultsFor all criteria of sagittal reformats, the segmented acquisition was statistically superior to the original. For all sharpness criteria of axial images, although the trend preferred the original acquisition, the difference was not significant. For artifact in axial images, the segmented acquisition was significantly superior.ConclusionsFor prostate MRI the new segmented acquisition significantly reduces the scalloping motion artifact that can be present in reformats due to long time lags between the acquisition of adjacent or overlapped slices while retaining image sharpness in the acquired axial slices.

PurposeThe goal of this work is to demonstrate 1 mm through‐plane resolution in multislice T2SE MRI using k‐space processing of overlapping slices and show applicability in prostate MRI.MethodsMultiple overlapped slices are acquired and Fourier transformed in the slice‐select direction. The slice profile is incorporated into a Tikhonov‐regularized reconstruction. Through‐plane resolution is tested in a resolution phantom. An anthropomorphic prostate phantom is used to study the SNR, and results are compared with theoretical prediction. The proposed method is tested in 16 patients indicated for clinical prostate MRI who gave written informed consent as overseen by our IRB. The “proposed” vs. “reference” multislice images are compared using multiple evaluation criteria for through‐plane resolution.ResultsThe modulation transfer function (MTF) plots of the resolution phantom show good modulation at frequency 0.5 lp/mm, demonstrating 1 mm through‐plane resolution restoration. The SNR measurements experimentally match the theoretically predicted values. The radiological evaluation shows that the proposed method is superior to the reference method for five criteria of sharpness but inferior with respect to artifacts.ConclusionsIn conjunction with overlapped slices a k‐space‐based reconstruction approach can be used to improve through‐plane resolution in multislice T2SE MRI. 1 mm resolution is demonstrated from 3.2 mm thick slices. The in vivo results from prostate MRI show improved sharpness when compared to the standard multislice method.

PurposeTo develop and validate a method for choosing the optimal two‐dimensional CAIPIRINHA kernel for subtraction contrast‐enhanced MR angiography (CE‐MRA) and estimate the degree of image quality improvement versus that of some reference acceleration parameter set at R ≥ 8.MethodsA metric based on patient‐specific coil calibration information was defined for evaluating optimality of CAIPIRINHA kernels as applied to subtraction CE‐MRA. Evaluation in retrospective studies using archived coil calibration data from abdomen, calf, foot, and hand CE‐MRA exams was accomplished with an evaluation metric comparing the geometry factor (g‐factor) histograms. Prospective calf, foot, and hand CE‐MRA studies were evaluated with vessel signal‐to‐noise ratio (SNR).ResultsRetrospective studies show g‐factor improvement for the selected CAIPIRINHA kernels was significant in the feet, moderate in the abdomen, and modest in the calves and hands. Prospective CE‐MRA studies using optimal CAIPIRINHA show reduced noise amplification with identical acquisition time in studies of the feet, with minor improvements in the hands and calves.ConclusionA method for selection of the optimal CAIPIRINHA kernel for high (R ≥ 8) acceleration CE‐MRA exams given a specific patient and receiver array was demonstrated. CAIPIRINHA optimization appears valuable in accelerated CE‐MRA of the feet and to a lesser extent in the abdomen. Magn Reson Med 73:2234–2242, 2015. © 2014 Wiley Periodicals, Inc.