Standard Single-shot Echo-planar Imaging Research Articles

Diffusion-weighted imaging of the scrotum: readout-segmented echo-planar imaging versus single-shot echo-planar imaging

Objective The purpose of this study was to compare the image quality of readout-segmented EPI (RS-EPI) and that of standard single-shot echo-planar imaging (SS-EPI) in patients with scrotal diseases. Methods Initial diagnosis of scrotal diseases were included in the prospective study, all patients underwent scrotum routine MRI and RS-EPI, SS-EPI sequence at 3.0 T. A total of 38 patients were recruited qualitative assessment, and 29 patients proved by operation and pathology (malignant 21 cases and benign 8 cases) were included quantitative analysis.For qualitative comparison of image quality, two readers independently assessed the two sets of DWI, which consisted of identification of structure and geometric distortion of scrotum (epididymis,testes, lesion) using a 5-point Likert scale. For assessment of image parameters, signal-to-noise ratio (SNR), contrast, contrast-to-noise ratio (CNR),apparent diffusion coefficient value of normal testis and testis distortion ratio of anatomical(T2WI)/DWI fusion image were calculated. Inter-observer agreement was assessed with the Kappa statistics, the differences of scores of RS-EPI and SS-EPI were compared by using Wilcoxon rank-sum test, and image parameters were compared by using paired sample t test. Results There was good reader agreement in the scores, the Kappa value were 0.77, 0.74, 0.80, 0.87. The difference of identification of structure and geometric distortion on RS-EPI and SS-EPI had statistic significance, the RS-EPI was superior to SS-EPI in image quality (all P<0.05).The SNR, contrast of benign lesion for two sequences had no statistic significance(P values were 0.352, 0.124, respectively), but the difference of CNR had statistic significance(P<0.05). The SNR,contrast and CNR of malignant lesion for two sequences had statistic significance (all P<0.05). The mean size of the testis was (35.61±9.78)mm, the mean distance in fusion image of RS-EPI or SS-EPI with T2WI were (3.80±1.32)mm and (7.54±2.62)mm, and the mean distortion ratios of the two set were (11.1±0.6)% and (22.4±19.2)%, respectively, the difference of two sets had statistic significance(P<0.05). There was no significant difference in the ADC obtained by using either DWI method(t=0.396,P=0.796), the mean ADC values of normal testes for RS-EPI and SS-EPI, respectively, were (1.18±0.06)×10-3mm2/s, (1.24±0.11)×10-3mm2/s. Conclusion RS-EPI DWI images is a feasible technique in the scrotum for producing high-resolution DWI with reduced geometric distortion and offers potentially superior image quality compared to SS-EPI at 3.0 T. Key words: Scrotum; Magnetic resonance imaging; Comparative study

Diffusion-Sensitized Ophthalmic Magnetic Resonance Imaging Free of Geometric Distortion at 3.0 and 7.0 T

This study is designed to examine the feasibility of diffusion-sensitized multishot split-echo rapid acquisition with relaxation enhancement (RARE) for diffusion-weighted ophthalmic imaging free of geometric distortions at 3.0 and 7.0 T in healthy volunteers and patients with intraocular masses. A diffusion-sensitized multishot split-echo RARE (ms-RARE) variant is proposed as an alternative imaging strategy for diffusion-weighted imaging. It is compared with standard single-shot echo planar imaging (EPI) and readout-segmented EPI in terms of geometric distortions in a structure phantom as well as in vivo at 3.0 and 7.0 T. To quantify geometric distortions, center of gravity analysis was carried out. Apparent diffusion coefficient (ADC) mapping in a diffusion phantom was performed to verify the diffusion sensitization within ms-RARE. An in vivo feasibility study in healthy volunteers (n = 10; mean age, 31 ± 7 years; mean body mass index, 22.6 ± 1.7 kg/m²) was conducted at 3.0 and 7.0 T to evaluate clinical feasibility of ms-RARE. As a precursor to a broader clinical study, patients (n = 6; mean age, 55 ± 12 years; mean body mass index, 27.5 ± 4.7 kg/m²) with an uveal melanoma and/or retinal detachment were examined at 3.0 and 7.0 T. In 1 case, the diseased eye was enucleated as part of the therapy and imaged afterward with magnetic resonance microscopy at 9.4 T. Macrophotography and histological investigation was carried out. For qualitative assessment of the image distortion, 3 independent readers reviewed and scored ms-RARE in vivo images for all subjects in a blinded reading session. Statistical significance in the difference of the scores (a) obtained for the pooled ms-RARE data with b = 0 and 300 s/mm² and (b) for the 3 readers was analyzed using the nonparametric Mann-Whitney test. The assessment of geometric integrity in phantom imaging revealed the ability of ms-RARE to produce distortion-free images. Unlike ms-RARE, modest displacements (2.3 ± 1.4 pixels) from the fast low angle shot imaging reference were observed for readout-segmented EPI, which were aggravated for single-shot EPI (8.3 ± 5.7 pixels). These observations were confirmed in the in vivo feasibility study including distortion-free diffusion-weighted ophthalmic images with a 0.5 × 0.5 × 5 mm³ spatial resolution at 3.0 T and as good as 0.2 × 0.2 × 2 mm³ at 7.0 T. The latter represents a factor of 40 enhancement in spatial resolution versus clinical protocols recently reported for diffusion-weighted imaging of the eye at 1.5 T. Mean ADC values within the vitreous body were (2.91 ± 0.14) × 10⁻³ mm²/s at 3.0 T and (2.93 ± 0.41) × 10⁻³ mm²/s at 7.0 T. Patient data showed severe retinal detachment in the anatomical images. Whereas the tumor remained undetected in T1-weighted and T2-weighted imaging at 3.0/7.0 T, in vivo ADC mapping using ms-RARE revealed the presence of a uveal melanoma with a significant contrast versus the surrounding subretinal hemorrhage. This observation was confirmed by high-resolution ex vivo magnetic resonance microscopy and histology. Qualitative analysis of image distortion in ms-RARE images obtained for all subjects yielded a mean ± SD image quality score of 1.06 ± 0.25 for b = 0 s/mm² and of 1.17 ± 0.49 for b = 300 s/mm². No significant interreader differences were observed for ms-RARE with a diffusion sensitization of b = 0 s/mm² and 300 s/mm². This work demonstrates the capability of diffusion-sensitized ms-RARE to acquire high-contrast, high-spatial resolution, distortion-free images of the eye and the orbit at 3.0 and 7.0 T. Geometric distortions that are observed for EPI-based imaging approaches even at lower field strengths are offset by fast spin-echo-based imaging techniques. The benefits of this improvement can be translated into the assessment of spatial arrangements of the eye segments and their masses with the ultimate goal to provide guidance during diagnostic treatment of ophthalmological diseases.

Comparison of field-of-view (FOV) optimized and constrained undistorted single shot (FOCUS) with conventional DWI for the evaluation of prostate cancer

ObjectivesQualitative and quantitative comparison of the application value of diffusion-weighted imaging (DWI) magnetic resonance imaging based on field-of-view (FOV) optimized and constrained undistorted single shot (FOCUS) with the standard single-shot echo-planar imaging (ss-EPI) in patients with prostate cancer. MethodsA total of 28 patients with 33 prostate cancers underwent ss-EPI and FOCUS DWI. Two independent readers assessed image studies. ResultsImage qualities of FOCUS were rated superior to ss-EPI (P<.001). The mean apparent diffusion coefficient value of 33 cancers was 974.030×10−6mm2/s and 941.727×10−6mm2/s, respectively, and the difference was statistically significant (t=2.579, P=.015). ConclusionsFOCUS as a high-resolution DWI technique has potential clinical utility.

Readout-segmented Echo-planar Imaging for Diffusion-weighted Imaging in the Pelvis at 3T—A Feasibility Study

Diffusion-weighted imaging (DWI) of the pelvis at 3T is prone to artifacts that diminish the image quality. Readout-segmented echo-planar imaging (RS-EPI) is a new DWI technique that can reduce the artifacts associated with standard single-shot echo-planar imaging (SS-EPI) DWI. The purpose of this study was to evaluate the feasibility and image quality of RS-EPI in pelvic DWI compared to SS-EPI on a 3T imaging system. Thirty patients underwent pelvic DWI on a 3T scanner with SS-EPI and RS-EPI techniques. Two blinded readers independently assessed each set of images for geometric distortion, image blurring, ghosting artifacts, lesion conspicuity, and overall image quality on a 7-point scale. Qualitative image scores were compared using paired Wilcoxon signed rank test. Interreader correlation was assessed by Spearman rank correlation. Geometric distortion, imaging blurring, ghosting artifacts, lesion conspicuity, and overall image quality were rated significantly better by both readers for RS-EPI technique (P < .01 for all parameters). There was moderate-high correlation between the readers (r = 0.649-0.752) for all parameters apart from lesion conspicuity (r = 0.351). Both readers preferred the RS-EPI set of DWI images in most of the cases (reader 1: 0.87, 95% CI 0.74-0.99; reader 2: 0.77, 95% CI 0.61-0.93). Mean difference and limits of agreement between apparent diffusion coefficient (ADC) values obtained from the two methods were 0.01 (-0.08, 0.10) × 10(-3) mm(2)/s. RS-EPI DWI images showed improved image quality compared to SS-EPI technique at 3T. RS-EPI is a feasible technique in the pelvis for producing high-resolution DWI.

High-resolution diffusion-weighted imaging for the separation of benign from malignant BI-RADS 4/5 lesions found on breast MRI at 3T

To determine whether readout-segmented echo-planar diffusion imaging (RESOLVE) improves separation of malignant versus benign lesions compared to standard single-shot echo-planar imaging (ss-EPI) on BI-RADS 4/5 lesions detected on breast magnetic resonance imaging (MRI). Consecutive 3T breast MRI studies with BI-RADS 4/5 designation and subsequent biopsy or benign mastectomy were retrospectively identified. Freehand regions of interest (ROIs) were drawn on lesions and also on normal background fibroglandular tissue for comparison. Lesion-to-background contrast was evaluated by normalizing signal intensity of the lesion ROI by the normal background tissue ROI at b = 800. Statistical analysis used the Mann-Whitney/Wilcoxon rank-sum test for unpaired and Wilcoxon signed-rank for paired comparisons. Of 38 lesions in 32 patients, 10 were malignant. Lesion-to-background contrast was higher on RESOLVE than ss-EPI (1.80 ± 0.71 vs. 1.62 ± 0.63, P = 0.03). Mean apparent diffusion coefficient (ADC) was the same or lower on RESOLVE than ss-EPI, and this effect was largest in malignant lesions (RESOLVE 0.90 ± 0.13; ss-EPI 1.00 ± 0.13; median difference -0.10 (95% confidence interval [CI]: -0.17, -0.02) × 10(-3) mm(2) /sec; P = 0.014). By either diffusion method, there was a statistically significant difference between benign and malignant mean ADC (P < 0.001). Increased lesion-to-background contrast and improved separation of benign from malignant lesions by RESOLVE compared to standard diffusion suggests that RESOLVE may show promise as an adjunct to clinical breast MRI.

Readout-segmented Echo-planar Imaging Improves the Diagnostic Performance of Diffusion-weighted MR Breast Examinations at 3.0 T

To qualitatively and quantitatively compare the diagnostic value of diffusion-weighted (DW) magnetic resonance (MR) imaging based on standard single-shot echo-planar imaging and readout-segmented echo-planar imaging in patients with breast cancer at 3.0 T. Institutional review board approval and written informed consent were obtained. Forty-seven patients with 49 histopathologically verified lesions were included in this study. In all patients, DW imaging, with single-shot echo-planar imaging and readout-segmented echo-planar imaging with comparable imaging parameters, was performed with a 3.0-T MR imager. Two independent readers visually assessed image quality and lesion conspicuity, and image properties (ie, signal-to-noise ratio, contrast, geometric distortions) were quantified. Regions of interest were drawn in all lesions (28 malignant, 21 benign) and in the normal breast parenchyma to investigate differences in apparent diffusion coefficient (ADC). Diagnostic accuracy was calculated on the basis of an ADC threshold of 1.25 × 10(-3) mm(2)/sec. Each reader found a higher diagnostic accuracy for readout-segmented (96%) than for single-shot (90%) echo-planar imaging. The area under the curve for readout-segmented echo-planar imaging (0.981) was significantly larger than for single-shot echo-planar imaging (0.867) (P = .026). There was no significant difference in the ADC obtained by using either DW imaging method. Lesion conspicuity and image quality of readout-segmented echo-planar imaging were rated superior to those of single-shot echo-planar imaging (P < .001). Readout-segmented echo-planar imaging reduced geometric distortions by a factor of three. DW imaging based on readout-segmented echo-planar imaging provided significantly higher image quality and lesion conspicuity than single-shot echo-planar imaging by reducing geometric distortions, image blurring, and artifact level with a clinical high-field-strength MR imager. Thereby, readout-segmented echo-planar imaging reached a higher diagnostic accuracy for the differentiation of benign and malignant breast lesions.

Detection of brain lesions at the skull base using diffusion-weighted imaging with readout-segmented echo-planar imaging and generalized autocalibrating partially parallel acquisitions

To analyze the value of readout-segmented echo-planar imaging (rs-EPI) with parallel imaging and a two-dimensional (2D) navigator-based reacquisition technique in the detection of brain lesions at the skull base. A total of 54 patients (male 37, female 17) with suspected skull-base intracranial lesions underwent magnetic resonance imaging (MRI), including pre-T1 weighted imaging, T2-weighted imaging, Fluid Attenuated Inversion Recovery (FLAIR), standard single shot echo-planar imaging diffusion weighted imaging (ss-EPI DWI) and rs-EPI DWI, post-contrast T1-weighted. The total number of lesions and the number of lesions at different sites on all MRI sequences were used as reference measures. Then differences in detecting lesions and image quality between standard ss-EPI DWI and rs-EPI DWI were analyzed. There was a significant difference in the total number of lesions detected by rs-EPI DWI and standard ss-EPI DWI (P = 0.01). But this difference was mainly due to an improved ability of rs-EPI DWI to detect lesions located in the anterior cranial fossa, compared to ss-EPI DWI (P=0.02); the ability of ss-EPI and rs-EPI DWI to detect lesions in the middle cranial fossa and posterior cranial fossa was not significantly different (P = 0.471, P = 0.486, respectively). For image quality, rs-EPI images were significantly better than standard ss-EPI DWI images (P<0.001). The rs-EPI DWI technique is a useful tool for the detection and evaluation of lesions located at the skull base.

High‐sensitivity cerebral perfusion mapping in mice by kbGRASE‐FAIR at 9.4 T

The combination of flow-sensitive alternating inversion recovery (FAIR) and single-shot k-space-banded gradient- and spin-echo (kbGRASE) is proposed here to measure perfusion in the mouse brain with high sensitivity and stability. Signal-to-noise ratio (SNR) analysis showed that kbGRASE-FAIR boosts image and temporal SNRs by 2.01 ± 0.08 and 2.50 ± 0.07 times, respectively, when compared with standard single-shot echo planar imaging (EPI)-FAIR implemented in our experimental systems, although the practically achievable spatial resolution was slightly reduced. The effects of varying physiological parameters on the precision and reproducibility of cerebral blood flow (CBF) measurements were studied following changes in anesthesia regime, capnia and body temperature. The functional MRI time courses with kbGRASE-FAIR showed a more stable response to 5% CO(2) than did those with EPI-FAIR. The results establish kbGRASE-FAIR as a practical and robust protocol for quantitative CBF measurements in mice at 9.4 T.