Simultaneous multi-slice echo planar diffusion weighted imaging of the liver and the pancreas: Optimization of signal-to-noise ratio and acquisition time and application to intravoxel incoherent motion analysis

Quantitative diffusion weighted imaging in patients with hepatocellular carcinoma: effects of simultaneous multi-slice acceleration and gadoxetic acid administration

PURPOSE

To investigate whether simultaneous multi-slice (SMS) acceleration and gadoxetic acid administration affect the quantitative apparent diffusion coefficient (ADC) and signal-to-noise ratio (SNR) measurement of DWI in patients with HCC.

METHODS

This prospective study initially enrolled 208 patients with clinically suspected HCC. Free breathing SMS-DWI and conventional DWI (CON-DWI) were performed before and after gadoxetic acid administration. Lesion conspicuity, ADCs and SNRs of the HCC lesion and normal liver parenchyma were independently measured by two radiologists. The paired t test or Wilcoxon signed rank test was used to evaluate the differences of lesion conspicuity, ADCs and SNRs between SMS-DWI and CON-DWI, as well as those before and after gadoxetic acid administration.

RESULTS

A total of 102 HCC patients (90 men and 12 women; mean age, 54.6 ± 11.7 years) were finally included for analysis. SMS-DWI and CON-DWI demonstrated comparable lesion conspicuity (P = 0.081-0.566). For the influence of SMS acceleration, the SNRs of liver parenchyma on enhanced SMS-DWI were significantly higher than enhanced CON-DWI (P = 0.015). For the influence of gadoxetic acid administration, the mean ADCs were significantly higher on enhanced SMS-DWI than unenhanced SMS-DWI (HCC, P = 0.013; liver parenchyma, P = 0.032).

CONCLUSION

Quantitative ADC measurements of HCC and liver parenchyma were not affected by SMS acceleration, and SMS-DWI can provide higher SNR than CON-DWI. However, the ADC measurements can be affected by gadoxetic acid administration on SMS-DWI, so it is recommended to perform SMS-DWI before gadoxetic acid administration.

Investigating the feasibility of differentiating MS active lesions from inactive ones using texture analysis and machine learning methods in DWI images

BACKGROUND

Magnetic resonance imaging (MRI) is commonly used in conjunction with a gadolinium-based contrast agent (GBCA) to distinguish active multiple sclerosis (MS) lesions. However, recent studies have raised concerns regarding the long-term effects of the accumulation of GBCA in the body. Thus, the purpose of this study is to investigate the possibility of using texture analysis in diffusion-weighted imaging (DWI) and machine learning algorithms to discriminate active from inactive MS lesions without the use of GBCA.

METHODS

To achieve this purpose, we introduce an image processing pipeline. In the proposed pipeline, following registration and alignment of slices, MS lesions from DWI images are segmented and quantized. Next, different texture analysis methods are employed to extract texture features from the lesions. Then, a two-stage feature reduction method is applied, in which the first stage involves a statistical t-test and the second stage relies on principal component analysis (PCA), sequential forward selection (SFS), sequential backward selection (SBS), and ReliefF algorithms. Finally, we use five classifiers logistic regression (LR), support vector machine (SVM), decision tree (DT), K nearest neighbor (KNN), and linear discriminant analysis (LDA) in a 5-fold cross-validation procedure to determine active and inactive MS lesions.

RESULTS

In this study, we collected and prepared 255 active/inactive MS lesions from MRI scans of 34 patients diagnosed with MS, with a mean age of 35.56±10.89. Among 89 texture features extracted, 63 features showed statistically significant differences between the means of active and inactive lesions (P<0.05). The SVM classifier with the PCA feature reduction algorithm demonstrated the best performance with an average accuracy of 0.960 (±0.024), specificity and precision of 1.0, sensitivity of 0.913 (±0.053), and AUC of 0.957 (±0.027).

CONCLUSION

Our study indicates that DWI changes detected using texture analysis-based machine learning models can precisely differentiate active from inactive MS lesions. This finding provides valuable clinical information for the early diagnosis and effective monitoring of MS disease.

The application of abbreviated MRI protocols in malignant liver lesions surveillance

Cancer is one of the leading public health problems globally. Since time is of the essence in oncology, the sooner an accurate diagnosis is made, the better the prognosis for patients. There is a growing need to find a flawless and fast imaging method for cancer detection, but also for its evaluation during treatment. In this respect, the possibilities and novelties of magnetic resonance imaging are particularly promising. Abbreviated magnetic resonance imaging (AMRI) protocols have aroused universal interest as a compromise between scanning time reduction and preservation of image quality. Shorter protocols focused on the detection of suspicious lesions with the most sensitive sequences could provide a diagnostic performance similar to the one of the standard protocol. The purpose of this article is to review the ongoing accomplishments in the use of AMRI protocols in liver metastases and HCC detection.

Technical Advancements in Abdominal Diffusion-weighted Imaging

Since its first observation in the 18th century, the diffusion phenomenon has been actively studied by many researchers. Diffusion-weighted imaging (DWI) is a technique to probe the diffusion of water molecules and create a MR image with contrast based on the local diffusion properties. The DWI pixel intensity is modulated by the hindrance the diffusing water molecules experience. This hindrance is caused by structures in the tissue and reflects the state of the tissue. This characteristic makes DWI a unique and effective tool to gain more insight into the tissue's pathophysiological condition. In the past decades, DWI has made dramatic technical progress, leading to greater acceptance in clinical practice. In the abdominal region, however, acquiring DWI with good quality is challenging because of several reasons, such as large imaging volume, respiratory and other types of motion, and difficulty in achieving homogeneous fat suppression. In this review, we discuss technical advancements from the past decades that help mitigate these problems common in abdominal imaging. We describe the use of scan acceleration techniques such as parallel imaging and compressed sensing to reduce image distortion in echo planar imaging. Then we compare techniques developed to mitigate issues due to respiratory motion, such as free-breathing, respiratory-triggering, and navigator-based approaches. Commonly used fat suppression techniques are also introduced, and their effectiveness is discussed. Additionally, the influence of the abovementioned techniques on image quality is demonstrated. Finally, we discuss the current and future clinical applications of abdominal DWI, such as whole-body DWI, simultaneous multiple-slice excitation, intravoxel incoherent motion, and the use of artificial intelligence. Abdominal DWI has the potential to develop further in the future, thanks to scan acceleration and image quality improvement driven by technological advancements. The accumulation of clinical proof will further drive clinical acceptance.

Influence of saturation effects on biexponential liver intravoxel incoherent motion

PURPOSE

Studies on intravoxel incoherent motion (IVIM) imaging in the liver have been carried out with different acquisition protocols. The number of acquired slices and the distances between slices can influence IVIM measurements due to saturation effects, but these effects have often been disregarded. This study investigated differences in biexponential IVIM parameters between two slice settings.

METHODS

Fifteen healthy volunteers (21-30 years) were examined at a field strength of 3 T. Diffusion-weighted images of the abdomen were acquired with 16 b values (0-800 s/mm² ), with four slices for the few slices setting and 24-27 slices for the many slices setting. Regions of interest were manually drawn in the liver. The data were fitted with a monoexponential signal curve and a biexponential IVIM curve, and biexponential IVIM parameters were determined. The dependence on the slice setting was assessed with Student's t test for paired samples (normally distributed IVIM parameters) and the Wilcoxon signed-rank test (non-normally distributed parameters).

RESULTS

None of the parameters were significantly different between the settings. For few slices and many slices, respectively, the mean values (SDs) for D $$ D $$ were 1.21 μm 2 / ms $$ 1.21{\upmu \mathrm{m}}^2/\mathrm{ms} $$ ( 0.19 μm 2 / ms $$ 0.19\kern0.3em {\upmu \mathrm{m}}^2/\mathrm{ms} $$ ) and 1.20 μm 2 / ms $$ 1.20{\upmu \mathrm{m}}^2/\mathrm{ms} $$ ( 0.11 μm 2 / ms $$ 0.11\kern0.3em {\upmu \mathrm{m}}^2/\mathrm{ms} $$ ); for f $$ f $$ they were 29.7% (6.2%) and 27.7% (3.6%); and for D * $$ {D}^{\ast } $$ they were 8.76 ⋅ 10 - 2 mm 2 / s $$ 8.76\cdot {10}^{-2}{\mathrm{mm}}^2/\mathrm{s} $$ ( 4.54 ⋅ 10 - 2 mm 2 / s $$ 4.54\cdot {10}^{-2}\kern0.3em {\mathrm{mm}}^2/\mathrm{s} $$ ) and 8.71 ⋅ 10 - 2 mm 2 / s $$ 8.71\cdot {10}^{-2}{\mathrm{mm}}^2/\mathrm{s} $$ ( 4.06 ⋅ 10 - 2 mm 2 / s $$ 4.06\cdot {10}^{-2}\kern0.3em {\mathrm{mm}}^2/\mathrm{s} $$ ).

CONCLUSION

Biexponential IVIM parameters in the liver are comparable among IVIM studies that use different slice settings, with mostly negligible saturation effects. However, this may not hold for studies that use much shorter TR.

Diffusion Weighted Imaging of the Abdomen and Pelvis: Recent Technical Advances and Clinical Applications

Diffusion weighted imaging (DWI) serves as one of the most important functional magnetic resonance imaging techniques in abdominal and pelvic imaging. It is designed to reflect the diffusion of water molecules and is particularly sensitive to the malignancies. Yet, the limitations of image distortion and artifacts in single-shot DWI may hamper its widespread use in clinical practice. With recent technical advances in DWI, such as simultaneous multi-slice excitation, computed or reduced field-of-view techniques, as well as advanced shimming methods, it is possible to achieve shorter acquisition time, better image quality, and higher robustness in abdominopelvic DWI. This review discussed the recent advances of each DWI approach, and highlighted its future perspectives in abdominal and pelvic imaging, hoping to familiarize physicians and radiologists with the technical improvements in this field and provide future research directions.

Feasibility of Simultaneous Multislice Acceleration Technique in Readout-Segmented Echo-Planar Diffusion-Weighted Imaging for Assessing Rectal Cancer

BACKGROUND

Readout-segmented echo-planar imaging (rs-EPI) with simultaneous multislice (SMS) technology has been successfully applied to tumor research in many organs, but no feasibility study in rectal cancer has been reported, and the optimal acceleration of SMS with rs-EPI in rectal cancer has not been well determined yet.

OBJECTIVE

To investigate the feasibility of SMS rs-EPI of rectal cancer with different acceleration factors (AF_s) and its influence on image quality, acquisition time and apparent diffusion coefficients (ADC_s) in comparison to conventional sequences.

METHODS

All patients underwent rs-EPI and SMS rs-EPI with AF_s of 2 and 3 (2 × SMS rs-EPI and 3 × SMS rs-EPI, respectively) using a 3T scanner. Acquisition times of the three rs-EPI sequences were measured. Image qualitative parameters (5-point Likert scale), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), geometric distortion, and apparent diffusion coefficient (ADC) values of the three sequences were compared.

RESULTS

A total of eighty-three patients were enrolled in our study. rs-EPI and 2 × SMS rs-EPI offered equivalently high overall image quality with a scan time reduction to nearly half (rs-EPI: 137 s, 2 × SM rs-EPI: 60 s). 3 × SMS rs-EPI showed significantly poorer image quality (p < 0.05). ADC values were significantly lower in 3 × SMS rs-EPI compared to rs-EPI in rectal tumors and normal tissue (tumor tissue: rs-EPI 1.19 ± 0.21 × 10^-3 mm²/s, 3 × SMS rs-EPI 1.10 ± 0.26 × 10^-3 mm²/s, p < 0.001; normal tissue: rs-EPI 1.68 ± 0.13 × 10^-3 mm²/s, 3 × SMS rs-EPI 1.54 ± 0.20 × 10^-3 mm²/s, p < 0.001).

CONCLUSIONS

SMS rs-EPI using an AF of 2 is feasible for rectal MRI resulting in substantial reductions in acquisition time while maintaining diagnostic image quality and similar ADC values to those of rs-EPI when the slice distance and number of shots are the same among three rs-EPI sequences.

Evaluating of the Quality of Hepatic Diffusion Weighted Imaging Using Multiband Imaging With Variable-Rate Selective Excitation

OBJECTIVE

To assess the image quality of diffusion-weighted imaging (DWI) using multiband (MB) imaging with variable-rate selective excitation (VERSE) and compare it to conventional DWI.

METHODS

We retrospectively evaluated hepatic DWI images of patients (n = 76) according to either the conventional method (SENSE, acceleration factor = 2) (n = 38) or fast scanning method (MB imaging with VERSE, acceleration factor = 2 × 2) (n = 38). We also conducted a volunteer study (n = 15) for those scanning methods. During quantitative analysis, the signal-to-noise ratio (SNR), apparent diffusion coefficient values, and contrast in the liver, spleen, and spinal cord were compared between the 2 groups. During qualitative analysis, all images were independently and blindly evaluated by 2 board-certified radiologists. The image contrast, noise, artifacts, and sharpness were assessed, and the performance of classification was measured using receiver operating characteristic curve analysis.

RESULTS

In the retrospective study, the SNRs of the hepatic parenchyma and spinal cord between the 2 protocols were significantly different (liver, 8.9 [interquartile range {IQR}, 7.6-12.2] vs 13.0 [IQR, 10.0-16.7]; P < 0.001 and spinal cord, 6.0 [IQR, 4.7-9.4] vs 4.3 [IQR, 3.8-6.8]; P < 0.02). No significant differences between the 2 protocols in the other retrospective analyses were noted. In the receiver operating characteristic curve analysis, area under the curve was 0.49 (95% confidence intervals, 0.40-0.58).

CONCLUSION

Multiband VERSE reduced scan time and SNR of hepatic DWI; however, subjective image quality parameters were not significantly impacted.

Design and Rationale for the Use of Magnetic Resonance Imaging Biomarkers to Predict Diabetes After Acute Pancreatitis in the Diabetes RElated to Acute Pancreatitis and Its Mechanisms Study: From the Type 1 Diabetes in Acute Pancreatitis Consortium

ABSTRACT

This core component of the Diabetes RElated to Acute pancreatitis and its Mechanisms (DREAM) study will examine the hypothesis that advanced magnetic resonance imaging (MRI) techniques can reflect underlying pathophysiologic changes and provide imaging biomarkers that predict diabetes mellitus (DM) after acute pancreatitis (AP). A subset of participants in the DREAM study will enroll and undergo serial MRI examinations using a specific research protocol. The aim of the study is to differentiate at-risk individuals from those who remain euglycemic by identifying parenchymal features after AP. Performing longitudinal MRI will enable us to observe and understand the natural history of post-AP DM. We will compare MRI parameters obtained by interrogating tissue properties in euglycemic, prediabetic, and incident diabetes subjects and correlate them with metabolic, genetic, and immunological phenotypes. Differentiating imaging parameters will be combined to develop a quantitative composite risk score. This composite risk score will potentially have the ability to monitor the risk of DM in clinical practice or trials. We will use artificial intelligence, specifically deep learning, algorithms to optimize the predictive ability of MRI. In addition to the research MRI, the DREAM study will also correlate clinical computed tomography and MRI scans with DM development.

High-Resolution Simultaneous Multi-Slice Accelerated Turbo Spin-Echo Musculoskeletal Imaging: A Head-to-Head Comparison With Routine Turbo Spin-Echo Imaging

Background/Aim: The turbo spin-echo (TSE) sequence is widely used for musculoskeletal (MSK) imaging; however, its acquisition speed is limited and can be easily affected by motion artifacts. We aimed to evaluate whether the use of a simultaneous multi-slice TSE (SMS-TSE) sequence can accelerate MSK imaging while maintaining image quality when compared with the routine TSE sequence.

Methods: We prospectively enrolled 71 patients [mean age, 37.43 ± 12.56 (range, 20–67) years], including 37 men and 34 women, to undergo TSE and SMS sequences. The total scanning times for the wrist, ankle and knee joint with routine sequence were 14.92, 13.97, and 13.48 min, respectively. For the SMS-TSE sequence, they were 7.52, 7.20, and 6.87 min. Quantitative parameters, including the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), were measured. Three experienced MSK imaging radiologists qualitatively evaluated the image quality of bone texture, cartilage, tendons, ligament, meniscus, and artifact using a 5-point evaluation system, and the diagnostic performance of the SMS-TSE sequences was evaluated.

Results: Compared with the routine TSE sequences, the scanning time was lower by 49.60, 48.46, and 49.04% using SMS-TSE sequences for the wrist, ankle, and knee joints, respectively. For the SNR comparison, the SMS-TSE sequences were significantly higher than the routine TSE sequence for wrist (except for Axial-T2WI-FS), ankle, and knee joint MR imaging (all p < 0.05), but no statistical significance was obtained for the CNR measurement (all p > 0.05, except for Sag-PDWI-FS in ankle joint). For the wrist joint, the diagnostic sensitivity, specificity, and accuracy were 88.24, 100, and 92%. For the ankle joint, they were 100, 75, and 93.33%. For the knee joint, they were 87.50, 85.71, and 87.10%.

Conclusion: The use of the SMS-TSE sequence in the wrist, ankle, and knee joints can significantly reduce the scanning time and show similar image quality when compared with the routine TSE sequence.

Accelerated Breast Diffusion-weighted Imaging Using Multiband Sensitivity Encoding with the CAIPIRINHA Method: Clinical Experience at 3 T

Purpose To examine the clinical value of multiband (MB) sensitivity encoding (SENSE)-accelerated diffusion-weighted imaging (DWI) for breast imaging by performing quantitative and qualitative comparisons with conventional diffusion-weighted echo-planar imaging, or conventional DWI (cDWI). Materials and Methods In this prospective study (ClinicalTrials.gov identifier NCT03607552), women with breast cancer were recruited from July 2018 to July 2019 to undergo additional MB SENSE DWI during clinical 3-T breast MRI examinations. The cDWI and MB SENSE DWI acquisitions were assessed both quantitatively and qualitatively. Regions of interest were defined for tumorous and normal tissue, and the tumor apparent diffusion coefficient (ADC), contrast-to-noise ratio (CNR), and signal index (SI) were calculated for both DWI methods. Three readers independently reviewed the two acquisitions side by side and provided relative image quality scores. Tumor ADC, CNR, and SI measures were compared between cDWI and MB SENSE DWI acquisitions by using a paired t test, and reader preferences were evaluated by using the sign test. Results The study included 38 women (median age, 48 years; range, 28-83 years). Overall agreement was good between cDWI and MB SENSE DWI tumor ADC measures (intraclass correlation coefficient, 0.87 [95% CI: 0.75, 0.94]), and no differences were evident in the ADC (median, 0.93 × 10^-3 mm²/sec vs 0.87 ×10^-3 mm²/sec; P = .50), CNR (2.2 vs 2.3; P = .17), or SI (9.2 vs 9.2; P = .23) measurements. The image quality of cDWI and MB SENSE DWI acquisitions were considered equal for 51% of images (58 of 114), whereas MB SENSE DWI was preferred more often than cDWI (37% [42 of 114] vs 12% [14 of 114]; P < .001). The preference for MB SENSE DWI was most often attributed to better fat suppression. Conclusion MB SENSE can be used to accelerate breast DWI acquisition times without compromising the image quality or the fidelity of quantitative ADC measurements. Keywords: MR-Diffusion-weighted Imaging, Breast, Comparative Studies, Technology Assessment Clinical trial registration no. NCT03607552 © RSNA, 2022.

Preliminary results of abdominal simultaneous multi-slice accelerated diffusion-weighted imaging with motion-correction in patients with cystic fibrosis and impaired compliance

OBJECTIVES

The aim of this prospective study was to compare scan time, image quality, signal-to-noise Ratio (SNR), and apparent diffusion coefficient (ADC) values of simultaneous multi-slice accelerated diffusion-weighted imaging with motion-correction (DWI SMS Moco) to standard diffusion-weighted imaging (sDWI) in free-breathing abdominal magnetic resonance imaging (MRI) in pediatric and young adult patients with cystic fibrosis (CF).

MATERIAL AND METHODS

16 patients (7 male and 9 female, 12-41 years old) with CF were examined prospectively in a single-center from November 2020 to March 2021 on a 1.5 Tesla clinical MR scanner. The characteristics of overall image quality and delimitability of mesenteric lymph nodes were evaluated using a 5-point Likert scale by two experienced pediatric radiologists independently from each other. Quantitative parameters with SNR and ADC values were assessed in 8 different locations and compared using a Wilcoxon signed-rank test.

RESULTS

The acquisition time for DWI SMS Moco was 32% shorter than for sDWI. Regarding quality comparison, overall image quality and delimitability of mesenteric lymph nodes were significant higher in DWI SMS Moco (p ≤ 0.05 for both readers). The readers preferred DWI SMS Moco to sDWI in all cases (16/16). Mean SNR values from DWI SMS Moco and sDWI were similar in 7 from 8 locations. The ADC values showed no significant difference between DWI SMS Moco and sDWI in any of the evaluated locations (p > 0.05).

CONCLUSIONS

The DWI SMS Moco improves overall image quality and delimitability of mesenteric lymph nodes compared to sDWI with similar SNR and ADC values and a distinguished reduction of scan time in free-breathing by one third. We conclude that MRI with DWI SMS Moco could be helpful in monitoring the effect of the high-efficiency modulator (HEM) therapy in cystic fibrosis (CF) patients homozygous or heterozygous for F508del in the abdomen.

Spiral 3D time-of-flight MR angiography for rapid non-contrast carotid artery imaging: Clinical feasibility and protocol optimization

PURPOSE

To assess the clinical feasibility of spiral 3D Time-Of-Flight (TOF) MR Angiography (MRA) sequence variants for rapid non-contrast carotid artery imaging.

METHODS

Nine different 3D TOF MRA sequences were acquired in nine healthy volunteers on a standard clinical 1.5 T scanner. Three cartesian sequences (fully sampled (10:15 min), accelerated with SENSE (05:08 min), accelerated with Compressed SENSE (03:32 min)) and six different spiral sequences were acquired (spiral acquisition windows ranging from 10 to 5 ms (01:32 min-03:05 min)). Three readers graded the images qualitatively in terms of overall image quality, vessel sharpness, inhomogeneous intraluminal signal, background noise, visualization of large and small vessels and overall impression of the number of visible vessels. Cross-sectional areas of the vessel lumen were measured and vessel sharpness was quantified.

RESULTS

The SENSE and Compressed SENSE accelerated cartesian sequences and the Spiral 6 ms and 5 ms sequences were deemed comparable to the fully sampled cartesian sequence in most qualitative categories (p > 0.05) based on exact binomial tests. The Spiral 6 ms and 5 ms sequences achieved a scan time reduction of 75.3% and 69.9% respectively compared to the fully sampled cartesian sequence. The spiral sequences (generally) exhibited improved subjective vessel sharpness (p < 0.01-p = 0.13) but increased background noise (p = 0.03-p = 0.25). Cross-sectional area measurements were similar between all sequences (Krippendorff's alpha: 0.955-0.982). Quantitative vessel sharpness was increased for all spiral sequences compared to all cartesian sequences (p = 0.004).

CONCLUSIONS

Spiral 3D TOF MRA sequences with a spiral acquisition window of 5 ms or 6 ms may be used for accurate, rapid, clinical non-contrast carotid artery imaging.

High-Resolution DWI with Simultaneous Multi-Slice Readout-Segmented Echo Planar Imaging for the Evaluation of Malignant and Benign Breast Lesions

To investigate the feasibility and effectiveness of high-resolution readout-segmented echo planar imaging (rs-EPI), diffusion-weighted imaging (DWI) is used simultaneously with multi-slice (SMS) imaging (SMS rs-EPI) for the differentiation of breast malignant and benign lesions in comparison to conventional rs-EPI on a 3T MR scanner. A total of 102 patients with 113 breast lesions underwent bilateral breast MRI using a prototype SMS rs-EPI sequence and a conventional rs-EPI sequence. Subjective image quality was assessed using a 5-point Likert scale (1 = poor, 5 = excellent). Signal-to-noise ratio (SNR), lesion contrast-to-noise ratio (CNR) and apparent diffusion coefficients (ADC) value of the lesion were measured for comparison. Receiver operating characteristic curve analysis was performed to evaluate the diagnosis performance of ADC, and the corresponding area under curve (AUC) was calculated. The image quality scores in anatomic distortion, lesion conspicuity, sharpness of anatomical details and overall image quality of SMS rs-EPI were significantly higher than those of conventional rs-EPI. CNR was enhanced in the high-resolution SMS rs-EPI acquisition (6.48 ± 1.71 vs. 4.23 ± 1.49; p < 0.001). The mean ADC value was comparable in SMS rs-EPI and conventional rs-EPI (benign 1.45 × 10⁻³ vs. 1.43 × 10⁻³ mm²/s, p = 0.702; malignant 0.91 × 10⁻³ vs. 0.89 × 10⁻³ mm²/s, p = 0.076). The AUC was 0.957 in SMS rs-EPI and 0.983 in conventional rs-EPI. SMS rs-EPI technique allows for higher spatial resolution and slight reduction of scan time in comparison to conventional rs-EPI, which has potential for better differentiation between malignant and benign lesions of the breast.

Clinical feasibility of simultaneous multislice acceleration in knee MRI

PURPOSE

To find the best simultaneous multislice (SMS) accelerated setting for clinical application in knee MRI.

MATERIAL AND METHODS

Thirty-three patients (mean age, 54 years; 21 women) who underwent knee MRI (conventional/SMS sequences) between June and October 2020 were enrolled. Two radiologists retrospectively evaluated sagittal T1- and T2-weighted conventional (2-fold parallel acquisition technique [PAT-2]) and SMS (SMS-2 [PAT-2 with 2-fold SMS], SMS-3, and SMS-4) images. For qualitative analysis, artifacts (zebra/residual aliasing) and diagnostic confidence for internal derangement of knee (bone marrow, cartilage, meniscus, anterior cruciate ligament, and synovium abnormalities) were evaluated. For quantitative analysis, contrast-to-noise ratios of bone marrow, meniscus, joint effusion, and ligament were evaluated.

RESULTS

Compared to PAT-2 (2 min 32 s), mean acquisition time was reduced by 47% in SMS-2; 64%, SMS-3; and 70%, SMS-4. In qualitative analysis, zebra artifacts were only seen on T2-weighted SMS images. The more SMS was applied, the more zebra and residual aliasing artifacts were seen and the lower diagnostic confidence was for internal derangement. However, qualitative analysis showed acceptable image quality in SMS-2 and SMS-3 images, but not in SMS-4 images. In quantitative analysis, SMS-4 images showed the lowest contrast-to-noise ratios and there were no significant differences among PAT-2, SMS-2, and SMS-3 images.

CONCLUSION

Applying SMS-3 to knee MRI reduced scan time and showed acceptable image quality compared to conventional (PAT-2). However, when evaluating SMS images, radiologists should know that when more SMS is applied, more zebra and residual aliasing artifacts appear.

Feasibility study of simultaneous multislice diffusion kurtosis imaging with different acceleration factors in the liver

Background

Simultaneous multislice diffusion-weighted imaging (SMS-DWI) has been used to reduce image acquisition time. The purpose of this study was to investigate the feasibility of diffusion kurtosis imaging (DKI) based on the SMS technique in the liver and the influence of this method compared with that of conventional DWI sequences on image quality and DKI-derived quantitative parameters.

Methods

Forty volunteers underwent SMS-DWI sequences with acceleration factors of 2 and 3 (SMS2-DWI, SMS3-DWI) and conventional DWI (C-DWI) of the liver with three b-values (50, 800, 2000 s/mm²) in a 3T system. Qualitative image quality parameters and quantitative measurements of the signal-to-noise ratio (SNR), mean kurtosis (MK), mean apparent diffusivity (MD) and apparent diffusion coefficient (ADC) for the liver were compared between the three sequences.

Results

The scan times of C-DWI, SMS2-DWI, and SMS3-DWI were 4 min 11 s, 2 min 2 s, and 1 min 34 s, respectively. For all image quality parameters, there were no significant differences observed between C-DWI and SMS2-DWI (all p > 0.05) in the images with b-values of 800 and 2000 s/mm². C-DWI and SMS2-DWI exhibited better scores than SMS3-DWI (all p < 0.01) in the images with b-values of 2000 s/mm². In the images with b-values of 800 s/mm², C-DWI and SMS2-DWI exhibited better scores than SMS3-DWI for artefacts and overall image quality (all p < 0.01), and C-DWI exhibited better scores than SMS3-DWI for the visibility of intrahepatic vessels (p < 0.001). There were no significant differences in the sharpness of the right lobe edge (p = 0.144), conspicuity of the left lobe (p = 0.370) or visibility of intrahepatic vessels (p = 0.109) between SMS2-DWI and SMS3-DWI. There were no significant differences in the sharpness of the right lobe edge (p = 0.066) or conspicuity of the left lobe (p = 0.131) between C-DWI and SMS3-DWI. For the b-value of 800 s/mm², there were no statistically significant differences between SMS2-DWI and C-DWI (p = 1.000) or between SMS2-DWI and SMS3-DWI (p = 0.059), whereas SMS3-DWI had a significantly lower SNR than C-DWI (p = 0.024). For the DKI-derived parameters (MK and MD) and ADC values, there were no significant differences between the three sequences (MK, p = 0.606; MD, p = 0.831; ADC, p = 0.264).

Conclusions

SMS-DWI with an acceleration factor of 2 is feasible for the liver, resulting in considerable reductions in scan time while maintaining similar image quality, comparable DKI parameters and ADC values compared with those of C-DWI.

Scan Time Reduction in Intravoxel Incoherent Motion Diffusion-Weighted Imaging and Diffusion Kurtosis Imaging of the Abdominal Organs: Using a Simultaneous Multislice Technique With Different Acceleration Factors

OBJECTIVE

To investigate the feasibility of quantitative intravoxel incoherent motion (IVIM) and diffusion kurtosis imaging (DKI) analyses in the upper abdominal organs by simultaneous multislice diffusion-weighted imaging (SMS-DWI).

SUBJECTS AND METHODS

In this prospective study, a total of 32 participants underwent conventional DWI (C-DWI) and SMS-DWI sequences with acceleration factors of 2 and 3 (SMS2-DWI and SMS3-DWI, respectively) in the upper abdomen with multiple b-values (0, 10, 20, 50, 80, 100, 150, 200, 500, 800, 1000, 1500, and 2000 seconds/mm2) on a 3 T system (MAGNETOM Prisma; Siemens Healthcare, Erlangen, Germany). Image quality and quantitatively measurements of apparent diffusion coefficient (ADC), true diffusion coefficient (D), pseudodiffusion coefficient (D*), perfusion fraction (f), mean kurtosis (MK), and mean apparent diffusivity (MD) for the liver, pancreas, kidney cortex and medulla, spleen, and erector spine muscle were compared between the 3 sequences.

RESULTS

The acquisition times for C-DWI, SMS2-DWI, and SMS3-DWI were 10 minutes 57 seconds, 5 minutes 9 seconds, and 3 minutes 54 seconds. For image quality parameters, C-DWI and SMS2-DWI yielded better results than SMS3-DWI (P < 0.05). SMS2-DWI had equivalent IVIM and DKI parameters compared with that of C-DWI (P > 0.05). No statistically significant differences in the ADC, D, f, and MD values between the 3 sequences (P > 0.05) were observed. The D* and MK values of the liver (P = 0.005 and P = 0.012) and pancreas (P = 0.019) between SMS3-DWI and C-DWI were significantly different.

CONCLUSIONS

SMS2-DWI can substantially reduce the scan time while maintaining equivalent IVIM and DKI parameters in the abdominal organs compared with C-DWI.

Emerging Imaging Biomarkers in Crohn Disease

ABSTRACT

In this review article, we present the latest developments in quantitative imaging biomarkers based on magnetic resonance imaging (MRI), applied to the diagnosis, assessment of response to therapy, and assessment of prognosis of Crohn disease. We also discuss the biomarkers' limitations and future prospects. We performed a literature search of clinical and translational research in Crohn disease using diffusion-weighted MRI (DWI-MRI), dynamic contrast-enhanced MRI (DCE-MRI), motility MRI, and magnetization transfer MRI, as well as emerging topics such as T1 mapping, radiomics, and artificial intelligence. These techniques are integrated in and combined with qualitative image assessment of magnetic resonance enterography (MRE) examinations. Quantitative MRI biomarkers add value to MRE qualitative assessment, achieving substantial diagnostic performance (area under receiver-operating curve = 0.8-0.95). The studies reviewed show that the combination of multiple MRI sequences in a multiparametric quantitative fashion provides rich information that may help for better diagnosis, assessment of severity, prognostication, and assessment of response to biological treatment. However, the addition of quantitative sequences to MRE examinations has potential drawbacks, including increased scan time and the need for further validation before being used in therapeutic drug trials as well as the clinic.

Performance of simultaneous multi-slice accelerated diffusion-weighted imaging for assessing focal renal lesions in pediatric patients with tuberous sclerosis complex

BACKGROUND

Diffusion-weighted imaging (DWI) is a useful MRI technique to characterize abdominal lesions in children, but long acquisition times can lead to image degradation. Simultaneous multi-slice accelerated DWI is a promising technique to shorten DWI scan times.

OBJECTIVE

To test the feasibility of simultaneous multi-slice DWI of the kidneys in pediatric patients with tuberous sclerosis complex (TSC) and to evaluate the accelerated protocol regarding image quality and quantitative apparent diffusion coefficient (ADC) values compared to standard echoplanar DWI sequence.

MATERIALS AND METHODS

We included 33 children and adolescents (12 female, 21 male; mean age 10±5 years) with TSC and renal cyst or angiomyolipoma on 3-tesla (T) MRI from 2017 to 2019. All studies included both free-breathing standard echoplanar DWI and simultaneous multi-slice DWI sequences. Subjective and quantitative image quality was evaluated using a predefined 5-point scale. ADC values were obtained for all renal cysts and angiomyolipomas ≥5 mm. All statistical analysis was performed using Stata/SE v15.1.

RESULTS

Simultaneous multi-slice DWI ADC values were slightly lower compared to standard echoplanar DWI for both renal cysts and angiomyolipomas (mean difference 0.05×10^-3 mm²/s, 95% confidence interval [CI] 0.40-0.50 and 0.024×10^-3 mm²/s, 95% CI 0.17-0.21, respectively, with P>0.1). Our results showed that renal lesions with ADC values >1.69×10^-3 mm²/s were all cysts, whereas lesions with values <1.16×10^-3 mm²/s were all angiomyolipomas. However, ADC values could not discriminate between lipid-rich and lipid-poor angiomyolipomas (P>0.1, for both sequences).

CONCLUSION

A 55% reduction in scan time was achieved using simultaneous multi-slice DWI for abdominal imaging in children with TSC, with near identical image quality as standard DWI. These results suggest that multi-slice techniques should be considered more broadly as an MRI acceleration technique in children.

Intravoxel incoherent motion magnetic resonance imaging: basic principles and clinical applications

The purpose of this article was to show basic principles, acquisition, advantages, disadvantages, and clinical applications of intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI). IVIM MRI as a method was introduced in the late 1980s, but recently it started attracting more interest thanks to its applications in many fields, particularly in oncology and neuroradiology. This imaging technique has been developed with the objective of obtaining not only a functional analysis of different organs but also different types of lesions. Among many accessible tools in diagnostic imaging, IVIM MRI aroused the interest of many researchers in terms of studying its applicability in the evaluation of abdominal organs and diseases. The major conclusion of this article is that IVIM MRI seems to be a very auspicious method to investigate the human body, and that nowadays the most promising clinical application for IVIM perfusion MRI is oncology. However, due to lack of standardisation of image acquisition and analysis, further studies are needed to validate this method in clinical practice.

An optimized b-value distribution for triexponential intravoxel incoherent motion (IVIM) in the liver

PURPOSE

To find an optimized b-value distribution for reproducible triexponential intravoxel incoherent motion (IVIM) exams in the liver.

METHODS

A numeric optimization of b-value distributions was performed using the triexponential IVIM equation and 27 different IVIM parameter sets. Starting with an initially optimized distribution of 6 b-values, the number of b-values was increased stepwise. Each new b-value was chosen from a set of 64 predefined b-values based on the computed summed relative mean error of the fitted triexponential IVIM parameters. This process was repeated for up to 100 b-values. In simulations and in vivo measurements, optimized b-value distributions were compared to 4 representative distributions found in literature.

RESULTS

The first 16 optimized b-values were 0, 0.3, 0.3, 70, 200, 800, 70, 1, 3.5, 5, 70, 1.2, 6, 45, 1.5, and 60 in units of s/mm² . Low b-values were much more frequent than high b-values. The optimized b-value distribution resulted in a higher fit stability compared to distributions used in literature in both, simulation and in vivo measurements. Using more than 6 b-values, ideally 16 or more, increased the fit stability considerably.

CONCLUSION

Using optimized b-values, the fit uncertainty in triexponential IVIM can be largely reduced. Ideally, 16 or more b-values should be acquired.

Accelerating acquisition of readout-segmented echo planar imaging with a simultaneous multi-slice (SMS) technique for diagnosing breast lesions

OBJECTIVES

To investigate the feasibility and effectiveness of SMS rs-EPI for evaluating breast lesions.

METHODS

This prospective study was approved by IRB. Ninety-six patients had 102 histopathologically verified lesions (80 malignant and 22 benign) that were evaluated. Conventional rs-EPI and SMS rs-EPI data were acquired on a 3T scanner. Mean kurtosis (MK), mean diffusion (MD), and apparent diffusion coefficient (ADC) values were quantitatively calculated for each lesion on both sequences. Images were qualitatively and quantitatively analyzed with respect to image sharpness, geometric distortion, lesion conspicuity, anatomic structure, overall image quality, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Student's t test, Pearson correlation, receiver operating characteristic curve, Wilcoxon rank sum test, and paired-sample t tests were used for statistical analysis.

RESULTS

Compared to conventional rs-EPI, the acquisition time of SMS rs-EPI was markedly reduced (2:17 min vs 4:27 min). Pearson's correlations showed excellent linear relationships for each parameter between conventional rs-EPI and SMS rs-EPI (MK, r = 0.908; MD, r = 0.938; and ADC, r = 0.975; p < 0.01 for all). Furthermore, SMS rs-EPI had similar diagnostic performance compared with conventional rs-EPI. SMS rs-EPI had comparable visual image quality as conventional rs-EPI, with excellent inter-reader reliability (ICC = 0.851-0.940). No differences existed between conventional rs-EPI and SMS rs-EPI for either SNR or CNR (p > 0.05).

CONCLUSIONS

Applying the SMS technique can significantly reduce the acquisition time and produce similar diagnostic accuracy while generating comparable image quality as the conventional rs-EPI.

KEY POINTS

• SMS rs-EPI reduces scan time from 4:27 min to 2:17 min compared with conventional rs-EPI. • SMS rs-EPI has a comparable diagnostic performance to conventional rs-EPI in the differentiation between malignant and benign breast lesions. • SMS rs-EPI demonstrates comparable image quality to conventional rs-EPI with shorter scan time.

Evaluation of simultaneous-multislice diffusion-weighted imaging of liver at 3.0 T with different breathing schemes

PURPOSE

To obtain the optimal simultaneous-multislice (SMS)-accelerated diffusion-weighted imaging (DWI) of the liver at 3.0 T MRI by systematically estimating the repeatability of apparent diffusion coefficient (ADC), signal-to-noise ratio (SNR) and image quality of different breathing schemes in comparison to standard DWI (STD) and other SMS sequences.

METHODS

In this institutional review board-approved prospective study, hepatic DWIs (b = 50, 300, 600 s/mm²) were performed in 23 volunteers on 3.0 T MRI using SMS and STD with breath-hold (BH-SMS, BH-STD), free-breathing (FB-SMS, FB-STD) and respiratory-triggered (RT-SMS, RT-STD). Reduction of scan time with SMS-acceleration was calculated. ADC and SNR were measured in nine anatomic locations and image quality was assessed on all SMS and STD sequences. An optimal SMS-DWI was decided by systematically comparing the ADC repeatability, SNR and image quality among above DWIs.

RESULTS

SMS-DWI reduced scan time significantly by comparison with corresponding STD-DWI (27 vs. 42 s for BH, 54 vs. 78 s for FB and 42 vs. 97 s for RT). In all DWIs, BH-SMS had the greatest intraobserver agreement (intraclass correlation coefficient (ICC): 0.920-0.944) and good interobserver agreement (ICC: 0.831-0.886) for ADC measurements, and had the best ADC repeatability (mean ADC absolute differences: 0.046-0.058 × 10^-3mm²/s, limits of agreement (LOA): 0.010-0.013 × 10^-3mm²/s) in nine locations. BH-SMS had the highest SNR in three representative sections except for RT-STD. There were no significant differences in image quality between BH-SMS and other DWI sequences (median BH-SMS: 4.75, other DWI: 4.5-5.0; P > 0.0.5).

CONCLUSION

BH-SMS provides considerable scan time reduction with good image quality, sufficient SNR and highest ADC repeatability on 3.0 T MRI, which is thus recommended as the optimal hepatic DWI sequence for those subjects with adequate breath-holding capability.

Simultaneous multi-slice accelerated diffusion-weighted imaging with higher spatial resolution for patients with liver metastases from neuroendocrine tumours

AIM

To evaluate the imaging characteristics of simultaneous multi-slice (SMS) accelerated diffusion-weighted imaging (DWI) with decreased section thickness, with and without motion correction, in comparison to conventional DWI (cDWI) for the detection of lesions in patients with neuroendocrine tumour (NET) liver metastases.

MATERIALS AND METHODS

Fifteen patients with NET liver metastases underwent cDWI (section thickness [SL]=4 mm) and SMS-DWI (SL=2 mm). Non-linear motion-corrected (Moco)-SMS-DWI was generated in addition to the original series. Qualitative imaging characteristics (five-point Likert scale), the number of high signal lesions, and the detectability and delineation of lesions were evaluated and compared using the Friedman and the Dunn-Bonferroni tests. The test-retest variability (TRV) of the cDWI and SMS-DWI techniques was investigated among 11 healthy volunteers who underwent cDWI (SL=4 mm) and SMS-DWI (SL=4 mm) twice. The Friedman and the Dunn-Bonferroni post-hoc tests were used to compare the mean apparent diffusion coefficient (ADC) and the TRV in different liver regions between the three series.

RESULTS

Moco-SMS-DWI demonstrated significantly superior overall image quality (p<0.001) with significantly fewer artefacts (p=0.003) than cDWI. The number of lesions detected by cDWI, SMS-DWI, and Moco-SMS-DWI were 348, 504, and 523, respectively. The detectability and delineation of the lesions and the ADC values were significantly higher on the SMS-DWI and Moco-SMS-DWI images than on the cDWI images (all p<0.001). Moco-SMS-DWI showed significantly higher TRV than cDWI in regions near the liver edge (p=0.018).

CONCLUSIONS

SMS-DWI achieves higher spatial resolution than cDWI within the same acquisition time, detects more lesions, and provides better lesion delineation. By applying motion correction, the TRV of DWI could be enhanced in regions near the liver edge.

Evaluation of trigeminal nerve tractography using two-fold-accelerated simultaneous multi-slice readout-segmented echo planar diffusion tensor imaging

OBJECTIVES

Simultaneous multi-slice (SMS) imaging with short repetition time (TR) accelerates diffusion tensor imaging (DTI) acquisitions. However, its impact when combined with readout-segmented echo planar imaging (RESOLVE) on the cranial nerves given the challenging skull base/posterior fossa terrain is unexplored. We evaluated the reliability of trigeminal nerve DTI metrics using SMS with RESOLVE-DTI.

METHODS

Eight healthy controls and six patients with unilateral trigeminal neuralgia (TN) underwent brain MRI scan. Three different RESOLVE-DTI protocols were performed on a 3-T MRI system: non-SMS (TR = 4330 ms), SMS with identical TR (4330 ms), and SMS with short TR (2400 ms). Pontine signal-to-noise ratio (SNR) and DTI metrics of the trigeminal nerve streamlines tracked by two independent raters using deterministic tractography and standardized tracking protocol were obtained. These were statistically analyzed and compared across the three protocols using intra-rater and inter-rater intraclass correlation coefficients (ICCs), one-way analysis of variance (ANOVA), post hoc analysis, and linear regression.

RESULTS

On visual screening, there were no artifacts across the trigeminal nerves. All data also cleared objective image quality assurance analysis. Pontine SNR was similar for the two SMS protocols and higher for the non-SMS RESOLVE-DTI (F_(2,36) = 4.40, p = 0.02). Intra-rater and inter-rater ICCs were very good (> 0.85). Trigeminal nerve DTI metrics were consistently measured by the three protocols, revealing significant linear relationships between non-SMS- and SMS-derived DTI metrics.

CONCLUSION

SMS RESOLVE-DTI enables fast and reliable evaluation of microstructural integrity of the trigeminal nerve, with potential application in the clinical management of TN.

KEY POINTS

• Readout-segmented diffusion-weighted echo planar imaging (RESOLVE-DTI) reduces image distortion artifacts in the posterior fossa but its long acquisition time limits clinical utility. • Simultaneous multi-slice (SMS) imaging combined with RESOLVE-DTI provides reliable trigeminal nerve tractography with potential applications in trigeminal neuralgia. • Two-fold-accelerated RESOLVE-DTI yields comparable trigeminal nerve streamlines and DTI metrics while near-halving acquisition time.

Feasibility of Simultaneous Multislice Acceleration Technique in Diffusion-Weighted Magnetic Resonance Imaging of the Rectum

Objective

To assess the feasibility of simultaneous multislice-accelerated diffusion-weighted imaging (SMS-DWI) of the rectum in comparison with conventional DWI (C-DWI) in rectal cancer patients.

Materials and Methods

This study included 65 patients with initially-diagnosed rectal cancer. All patients underwent C-DWI and SMS-DWI with acceleration factors of 2 and 3 (SMS2-DWI and SMS3-DWI, respectively) using a 3T scanner. Acquisition times of the three DWI sequences were measured. Image quality in the three DWI sequences was reviewed by two independent radiologists using a 4-point Likert scale and subsequently compared using the Friedman test. Apparent diffusion coefficient (ADC) values for rectal cancer and the normal rectal wall were compared among the three sequences using repeated measures analysis of variance.

Results

Acquisition times using C-DWI, SMS2-DWI, and SMS3-DWI were 173 seconds, 107 seconds, (38.2% shorter than C-DWI), and 77 seconds (55.5% shorter than C-DWI), respectively. For all image quality parameters other than distortion (margin sharpness, artifact, lesion conspicuity, and overall image quality), C-DWI and SMS2-DWI yielded better results than did SMS3-DWI (Ps < 0.001), with no significant differences observed between C-DWI and SMS2-DWI (Ps ≥ 0.054). ADC values of rectal cancer (p = 0.943) and normal rectal wall (p = 0.360) were not significantly different among C-DWI, SMS2-DWI, and SMS3-DWI.

Conclusion

SMS-DWI using an acceleration factor of 2 is feasible for rectal MRI resulting in substantial reductions in acquisition time while maintaining diagnostic image quality and similar ADC values to those of C-DWI.

Feasibility study of using simultaneous multi-slice RESOLVE diffusion weighted imaging to assess parotid gland tumors: comparison with conventional RESOLVE diffusion weighted imaging

Background

To evaluate the feasibility of using simultaneous multi-slice (SMS) readout segmentation of long variable echo-trains (RESOLVE) diffusion-weighted imaging (DWI) to assess parotid gland tumors, compared with conventional RESOLVE DWI.

Methods

From September 2018 to December 2018, 20 consecutive patients with parotid tumors who underwent MRI scan for pre-surgery evaluation were enrolled. SMS-RESOLVE DWI and conventional RESOLVE DWI were scanned with matched imaging parameters, respectively. The scan time of two DWI sequences was recorded. Qualitative (anatomical structure differentiation, lesion display, artifact, and overall image quality) and quantitative (apparent diffusion coefficient, ADC; ratio of signal-to-noise ratio, SNR ratio; ratio of contrast-to-noise ratio, CNR ratio) assessments of image quality were performed, and compared between SMS-RESOLVE DWI and conventional RESOLVE DWI by using Paired t-test. Two-sided P value less than 0.05 indicated significant difference.

Results

The scan time was 3 min and 41 s for SMS-RESOLVE DWI, and 5 min and 46 s for conventional RESOLVE DWI. SMS-RESOLVE DWI produced similar qualitative image quality with RESOLVE DWI (anatomical structure differentiation, P = 0.164; lesion display, P = 0.193; artifact, P = 0.330; overall image quality, P = 0.083). Meanwhile, there were no significant difference on ADC_Lesion (P = 0.298), ADC_Masseter (P = 0.122), SNR ratio (P = 0.584) and CNR ratio (P = 0.217) between two DWI sequences.

Conclusion

Compared with conventional RESOLVE DWI, SMS-RESOLVE DWI could provide comparable image quality using markedly reduced scan time. SMS could increase the clinical usability of RESOLVE technique for DWI of parotid gland.

Accurate intravoxel incoherent motion parameter estimation using Bayesian fitting and reduced number of low b-values

PURPOSE

Intravoxel incoherent motion (IVIM) magnetic resonance imaging is a potential noninvasive technique for the diagnosis of brain tumors. However, perfusion-related parameter mapping is a persistent problem. The purpose of this paper is to investigate the IVIM parameter mapping of brain tumors using Bayesian fitting and low b-values.

METHODS

Bayesian shrinkage prior (BSP) fitting method and different low b-value distributions were used to estimate IVIM parameters (diffusion D, pseudo-diffusion D*, and perfusion fraction F). The results were compared to those obtained by least squares (LSQ) on both simulated and in vivo brain data. Relative error (RE) and reproducibility were used to evaluate the results. The differences of IVIM parameters between brain tumor and normal regions were compared and used to assess the performance of Bayesian fitting in the IVIM application of brain tumor.

RESULTS

In tumor regions, the value of D* tended to be decreased when the number of low b-values was insufficient, especially with LSQ. BSP required less low b-values than LSQ for the correct estimation of perfusion parameters of brain tumors. The IVIM parameter maps of brain tumors yielded by BSP had smaller variability, lower RE, and higher reproducibility with respect to those obtained by LSQ. Obvious differences were observed between tumor and normal regions in parameters D (P < 0.05) and F (P < 0.001), especially F. BSP generated fewer outliers than LSQ, and distinguished better tumors from normal regions in parameter F.

CONCLUSIONS

Intravoxel incoherent motion parameters clearly allow brain tumors to be differentiated from normal regions. Bayesian fitting yields robust IVIM parameter mapping with fewer outliers and requires less low b-values than LSQ for the parameter estimation.

Rapid Imaging: Recent Advances in Abdominal MRI for Reducing Acquisition Time and Its Clinical Applications

Magnetic resonance imaging (MRI) plays an important role in abdominal imaging. The high contrast resolution offered by MRI provides better lesion detection and its capacity to provide multiparametric images facilitates lesion characterization more effectively than computed tomography. However, the relatively long acquisition time of MRI often detrimentally affects the image quality and limits its accessibility. Recent developments have addressed these drawbacks. Specifically, multiphasic acquisition of contrast-enhanced MRI, free-breathing dynamic MRI using compressed sensing technique, simultaneous multi-slice acquisition for diffusion-weighted imaging, and breath-hold three-dimensional magnetic resonance cholangiopancreatography are recent notable advances in this field. This review explores the aforementioned state-of-the-art techniques by focusing on their clinical applications and potential benefits, as well as their likely future direction.

Technological Advances of Magnetic Resonance Imaging in Today's Health Care Environment

Today's health care environment is shifting rapidly, driven by demographic change and high economic pressures on the system. Furthermore, modern precision medicine requires highly accurate and specific disease diagnostics in a short amount of time. Future imaging technology must adapt to these challenges.Demographic change necessitates scanner technologies tailored to the needs of an aging and increasingly multimorbid patient population. Accordingly, examination times have to be short enough that diagnostic images can be generated even for patients who can only lie in the scanner for a short time because of pain or with low breath-hold capacity.For economic reasons, the rate of nondiagnostic scans due to artifacts should be reduced as far as possible. As imaging plays an increasingly pivotal role in clinical-therapeutic decision making, magnetic resonance (MR) imaging facilities are confronted with an ever-growing number of patients, emphasizing the need for faster acquisitions while maintaining image quality.Lastly, modern precision medicine requires high and standardized image quality as well as quantifiable data in order to develop image-based biomarkers on which subsequent treatment management can rely.In recent decades, a variety of approaches have addressed the challenges of high throughput, demographic change, and precision medicine in MR imaging. These include field strength, gradient, coil and sequence development, as well as an increasing consideration of artificial intelligence. This article reviews state-of-the art MR technology and discusses future implementation from the perspective of what we know today.

Improved Liver Diffusion-Weighted Imaging at 3 T Using Respiratory Triggering in Combination With Simultaneous Multislice Acceleration

OBJECTIVES

The aim of this study was to retrospectively compare optimized respiratory-triggered diffusion-weighted imaging with simultaneous multislice acceleration (SMS-RT-DWI) of the liver with a standard free-breathing echo-planar DWI (s-DWI) protocol at 3 T with respect to the imaging artifacts inherent to DWI.

MATERIALS AND METHODS

Fifty-two patients who underwent a magnetic resonance imaging study of the liver were included in this retrospective study. Examinations were performed on a 3 T whole-body magnetic resonance system (MAGNETOM Skyra; Siemens Healthcare, Erlangen, Germany). In all patients, both s-DWI and SMS-RT-DWI of the liver were obtained. Images were qualitatively evaluated by 2 independent radiologists with regard to overall image quality, liver edge sharpness, sequence-related artifacts, and overall scan preference. For quantitative evaluation, signal-to-noise ratio was measured from signal-to-noise ratio maps. The mean apparent diffusion coefficient (ADC) was measured in each liver quadrant. The Wilcoxon rank-sum test was used for analysis of the qualitative parameters and the paired Student t test for quantitative parameters.

RESULTS

Overall image quality, liver edge sharpness, and sequence-related artifacts of SMS-RT-DWI received significantly better ratings compared with s-DWI (P < 0.05 for all). For 90.4% of the examinations, both readers overall preferred SMS-RT-DWI to s-DWI. Acquisition time for SMS-RT-DWI was 34% faster than s-DWI. Signal-to-noise ratio values were significantly higher for s-DWI at b50 but did not statistically differ at b800, and they were more homogenous for SMS-RT-DWI, with a significantly lower standard deviation at b50. Mean ADC values decreased from the left to right hepatic lobe as well as from cranial to caudal for s-DWI. With SMS-RT-DWI, mean ADC values were homogeneous throughout the liver.

CONCLUSIONS

Optimized, multislice, respiratory-triggered DWI of the liver at 3 T substantially improves image quality with a reduced scan acquisition time compared with s-DWI.

Comparison of free breathing and respiratory triggered diffusion-weighted imaging sequences for liver imaging

BACKGROUND

Diffusion-weighted imaging (DWI) has become a useful tool in the detection, characterization, and evaluation of response to treatment of many cancers, including malignant liver lesions. DWI offers higher image contrast between lesions and normal liver tissue than other sequences. DWI images acquired at two or more b-values can be used to derive an apparent diffusion coefficient (ADC). DWI in the body has several technical challenges. This include ghosting artifacts, mis-registration and susceptibility artifacts. New DWI sequences have been developed to overcome some of these challenges. Our goal is to evaluate 3 new DWI sequences for liver imaging.

AIM

To qualitatively and quantitatively compare 3 DWI sequences for liver imaging: free-breathing (FB), simultaneous multislice (SMS), and prospective acquisition correction (PACE).

METHODS

Magnetic resonance imaging (MRI) was performed in 20 patients in this prospective study. The MR study included 3 separate DWI sequences: FB-DWI, SMS-DWI, and PACE-DWI. The image quality, mean ADC, standard deviations (SD) of ADC, and ADC histogram were compared. Wilcoxon signed-rank tests were used to compare qualitative image quality. A linear mixed model was used to compare the mean ADC and the SDs of the ADC values. All tests were 2-sided and P values of < 0.05 were considered statistically significant.

RESULTS

There were 56 lesions (50 malignant) evaluated in this study. The mean qualitative image quality score of PACE-DWI was 4.48. This was significantly better than that of SMS-DWI (4.22) and FB-DWI (3.15) (P < 0.05). Quantitatively, the mean ADC values from the 3 different sequences did not significantly differ for each liver lesion. FB-DWI had a markedly higher variation in the SD of the ADC values than did SMS-DWI and PACE-DWI. We found statistically significant differences in the SDs of the ADC values for FB-DWI vs PACE-DWI (P < 0.0001) and for FB-DWI vs SMS-DWI (P = 0.03). The SD of the ADC values was not statistically significant for PACE-DWI and SMS-DWI (P = 0.18). The quality of the PACE-DWI ADC histograms were considered better than the SMS-DWI and FB-DWI.

CONCLUSION

Compared to FB-DWI, both PACE-DWI and SMS-DWI provide better image quality and decreased quantitative variability in the measurement of ADC values of liver lesions.

Topics on quantitative liver magnetic resonance imaging

Liver magnetic resonance imaging (MRI) is subject to continuous technical innovations through advances in hardware, sequence and novel contrast agent development. In order to utilize the abilities of liver MR to its full extent and perform high-quality efficient exams, it is mandatory to use the best imaging protocol, to minimize artifacts and to select the most adequate type of contrast agent. In this article, we review the routine clinical MR techniques applied currently and some latest developments of liver imaging techniques to help radiologists and technologists to better understand how to choose and optimize liver MRI protocols that can be used in clinical practice. This article covers topics on (I) fat signal suppression; (II) diffusion weighted imaging (DWI) and intravoxel incoherent motion (IVIM) analysis; (III) dynamic contrast-enhanced (DCE) MR imaging; (IV) liver fat quantification; (V) liver iron quantification; and (VI) scan speed acceleration.

Modulating Diffusion-Weighted Magnetic Resonance Imaging for Screening in Oncologic Tertiary Prevention: A Prospective Ex Vivo and In Vivo Study

INTRODUCTION

Diffusion-weighted imaging (DWI) is an important part of oncological magnetic resonance imaging (MRI) examinations, especially for tertiary cancer prevention in terms of early detection of recurrent disease. However, abdominal studies can be challenged by motion artifacts, poor signal-to-noise ratios, and visibility of retroperitoneal structures, which necessitates sequence optimization depending on the investigated region. This study aims at prospectively evaluating an adapted DWI sequence ex vivo and in vivo in oncologic patients undergoing abdominal MRI.

METHODS

This institutional review board-approved, prospective study included phantom measurements, volunteer examinations, and oncologic patient examinations of the abdomen. Fifty-seven MRI examinations in 54 patients (mean age, 58 years; range, 21-90 years) were included into the analysis. The MRI examination were performed at a 1.5 T MRI scanner (MAGNETOM Aera; Siemens Healthcare, Erlangen, Germany) and included both a standard EPI-DWI (s-DWI; b = 50, 900 s/mm) and an adapted DWI (opt-DWI; EPI-DWI with b = 0, 50, 900, 1500 s/mm, acquisition with higher spatial resolution and optimized processing for the abdomen including motion correction, adaptive image combination, and background suppression). For b = 900 s/mm, the ratio of signal intensity in the normal tissue and the standard deviation of the noise in the surrounding air was quantitatively calculated; image quality and tissue differentiation parameters were rated by 2 independent, blinded readers using a 5-point Likert scale. Statistics included Wilcoxon signed-rank test and kappa statistic (P < 0.05/0.0125 after Bonferroni correction).

RESULTS

The DWI phantom demonstrated an optimized contour sharpness and inlay differentiation for opt-DWI. The apparent ratio of normal tissue signal/standard deviation of background noise at b = 900 s/mm of the right/left hemiabdomen was significantly increased in opt-DWI (mean, 71.9 ± 23.5/86.0 ± 43.3) versus s-DWI (mean, 51.4 ± 15.4/63.4 ± 36.5; P < 0.001). Image quality parameters (contour sharpness and tissue differentiation of upper abdominal and retroperitoneal structures) were significantly increased in opt-DWI versus s-DWI (P < 0.001). Interreader reliability test showed good agreement (kappa = 0.768; P < 0.001).

DISCUSSION

This study prospectively evaluated the potential of adapted DWI for screening in tertiary prevention of oncologic patients. An optimized DWI protocol with advanced processing achieved improved image quality in quantitative and qualitative analyses. Oncological optimization of DWI should be performed before its application in cancer patients to improve both screening and follow-up examinations, to better unleash the diagnostic potential of DWI.

Performance of an Automated Versus a Manual Whole-Body Magnetic Resonance Imaging Workflow

OBJECTIVES

The aim of this study was to evaluate the performance of an automated workflow for whole-body magnetic resonance imaging (WB-MRI), which reduces user interaction compared with the manual WB-MRI workflow.

MATERIALS AND METHODS

This prospective study was approved by the local ethics committee. Twenty patients underwent WB-MRI for myopathy evaluation on a 3 T MRI scanner. Ten patients (7 women; age, 52 ± 13 years; body weight, 69.9 ± 13.3 kg; height, 173 ± 9.3 cm; body mass index, 23.2 ± 3.0) were examined with a prototypical automated WB-MRI workflow, which automatically segments the whole body, and 10 patients (6 women; age, 35.9 ± 12.4 years; body weight, 72 ± 21 kg; height, 169.2 ± 10.4 cm; body mass index, 24.9 ± 5.6) with a manual scan. Overall image quality (IQ; 5-point scale: 5, excellent; 1, poor) and coverage of the study volume were assessed by 2 readers for each sequence (coronal T2-weighted turbo inversion recovery magnitude [TIRM] and axial contrast-enhanced T1-weighted [ce-T1w] gradient dual-echo sequence). Interreader agreement was evaluated with intraclass correlation coefficients. Examination time, number of user interactions, and MR technicians' acceptance rating (1, highest; 10, lowest) was compared between both groups.

RESULTS

Total examination time was significantly shorter for automated WB-MRI workflow versus manual WB-MRI workflow (30.0 ± 4.2 vs 41.5 ± 3.4 minutes, P < 0.0001) with significantly shorter planning time (2.5 ± 0.8 vs 14.0 ± 7.0 minutes, P < 0.0001). Planning took 8% of the total examination time with automated versus 34% with manual WB-MRI workflow (P < 0.0001). The number of user interactions with automated WB-MRI workflow was significantly lower compared with manual WB-MRI workflow (10.2 ± 4.4 vs 48.2 ± 17.2, P < 0.0001). Planning efforts were rated significantly lower by the MR technicians for the automated WB-MRI workflow than for the manual WB-MRI workflow (2.20 ± 0.92 vs 4.80 ± 2.39, respectively; P = 0.005). Overall IQ was similar between automated and manual WB-MRI workflow (TIRM: 4.00 ± 0.94 vs 3.45 ± 1.19, P = 0.264; ce-T1w: 4.20 ± 0.88 vs 4.55 ± .55, P = 0.423). Interreader agreement for overall IQ was excellent for TIRM and ce-T1w with an intraclass correlation coefficient of 0.95 (95% confidence interval, 0.86-0.98) and 0.88 (95% confidence interval, 0.70-0.95). Incomplete coverage of the thoracic compartment in the ce-T1w sequence occurred more often in the automated WB-MRI workflow (P = 0.008) for reader 2. No other significant differences in the study volume coverage were found.

CONCLUSIONS

In conclusion, the automated WB-MRI scanner workflow showed a significant reduction of the examination time and the user interaction compared with the manual WB-MRI workflow. Image quality and the coverage of the study volume were comparable in both groups.

Abbreviated MRI Protocols for the Abdomen

Technical advances in MRI have improved image quality and have led to expanding clinical indications for its use. However, long examination and interpretation times, as well as higher costs, still represent barriers to use of MRI. Abbreviated MRI protocols have emerged as an alternative to standard MRI protocols. These abbreviated MRI protocols seek to reduce longer MRI protocols by eliminating unnecessary or redundant sequences that negatively affect cost, MRI table time, patient comfort, image quality, and image interpretation time. However, the diagnostic information is generally not compromised. Abbreviated MRI protocols have already been used successfully for hepatocellular carcinoma screening, for prostate cancer detection, and for screening for nonalcoholic fatty liver disease as well as monitoring patients with this disease. It has been reported that image acquisition time and costs can be considerably reduced with abbreviated MRI protocols, compared with standard MRI protocols, while maintaining a similar sensitivity and accuracy. Nevertheless, multiple applications still need to be explored in the abdomen and pelvis (eg, surveillance of metastases to the liver; follow-up of cystic pancreatic lesions, adrenal incidentalomas, and small renal masses; evaluation of ovarian cysts in postmenopausal women; staging of cervical and uterine corpus neoplasms; evaluation of müllerian duct anomalies). This article describes some successful applications of abbreviated MRI protocols, demonstrates how they can help in improving the MRI workflow, and explores potential future directions. ^©RSNA, 2019.

Implementation of a 5-Minute Magnetic Resonance Imaging Screening Protocol for Prostate Cancer in Men With Elevated Prostate-Specific Antigen Before Biopsy

PURPOSE

The aims of this study were to establish a 5-minute magnetic resonance (MR) screening protocol for prostate cancer in men before biopsy and to evaluate effects on Prostate Imaging Reporting and Data System (PI-RADS) V2 scoring in comparison to a conventional, fully diagnostic multiparametric MR imaging (mpMRI) approach.

MATERIALS AND METHODS

Fifty-two patients with elevated prostate-specific antigen levels and without prior biopsy were prospectively included in this institutional review board-approved study. In all patients, an mpMRI protocol according to the PI-RADS recommendations was acquired on a 3 T MRI system. In addition, an accelerated diffusion-weighted imaging sequence was acquired using simultaneous multislice technique (DW-EPISMS). Two readers independently evaluated the images for the presence/absence of prostate cancer according to the PI-RADS criteria and for additional findings. In a first reading session, only the screening protocol consisting of axial T2-weighted and DW-EPISMS images was made available. In a subsequent reading session, the mpMRI protocol was assessed blinded to the results of the first reading, serving as reference standard.

RESULTS

Both readers successfully established a final diagnosis according to the PI-RADS criteria in the screening and mpMRI protocol. Mean lesion size was 1.2 cm in the screening and 1.4 cm in the mpMRI protocol (P = 0.4) with 35% (18/52) of PI-RADS IV/V lesions. Diagnostic performance of the screening protocol was excellent with a sensitivity and specificity of 100% for both readers with no significant differences in comparison to the mpMRI standard (P = 1.0). In 3 patients, suspicious lymph nodes were reported as additional finding, which were equally detectable in the screening and mpMRI protocol.

CONCLUSIONS

A 5-minute MR screening protocol for prostate cancer in men with elevated prostate-specific antigen levels before biopsy is applicable for clinical routine with similar diagnostic performance as the full diagnostic mpMRI approach.

Accelerated diffusion-weighted imaging for lymph node assessment in the pelvis applying simultaneous multislice acquisition: A healthy volunteer study

To evaluate the feasibility of accelerated simultaneous multislice diffusion weighted sequences (SMS-DWI) for lymph node detection in the abdominopelvic region. Sequences were evaluated regarding the number and depiction of lymph nodes detected with SMS-DWI compared with conventional diffusion weighted sequences, the most suitable SMS- acceleration factor, signal-to-noise ratio (SNR), and the overall acquisition time (TA).Eight healthy volunteers (4 men, 4 women; age range 21-39 years; median age 25 years) were examined in the pelvic region at 3T using a conventional DWI sequence and a SMS DWI sequence with different acceleration factors (AF: 2-3). Moreover, a SMS DWI sequence with AF 3 and higher slice resolution was applied. For morphological correlation of the lymph nodes and as a reference standard, an isotropic 3-dimensional T2-weighted fast-spin-echo sequence with high sampling efficiency (SPACE) was acquired. Two radiologists reviewed each DWI sequence and assessed the number of lymph nodes and the overall image quality. For each DWI sequence, SNR, SNR efficiency per time, contrast to noise (CNR), and ADC values were calculated. Values were statistically compared using a Wilcoxon test (P < .05).Overall, scan time of SMS-DWI with AF2 (AF3) decreased by 46.9% (57.2%) with respect to the conventional DWI. Compared with the SPACE sequence, the detection rate was 89.6% for conventional DWI, 69.4% for SMS-DWI with AF2, and 59.9% for SMS-DWI with AF3. The highly resolved SMS-DWI with AF3 leads to a scan time reduction of 46.9% and detection rate of 83.0%. SNR and CNR were lower in the accelerated sequences (up to 51.0%, P < .001) as compared with the conventional DWI. SNR efficiency decreased to 19.3% for AF2 and to 31.3% for AF3. In the highly resolved dataset, an SNR efficiency reduction of 51.2% was found.This study showed that lymph node detection in the abdominopelvic region with accelerated SMS-DWI sequences is feasible whereby an AF of 2 represents the best compromise between image quality, SNR, CNR, TA, and detection rate.

Assessment of different mathematical models for diffusion-weighted imaging as quantitative biomarkers for differentiating benign from malignant solid hepatic lesions

To quantitatively compare the monoexponential, biexponential, and stretched‐exponential diffusion‐weighted imaging (DWI) models in differentiating benign from malignant solid hepatic lesions. The institutional review board approved this retrospective study and waived the informed consent requirement. A total of 188 patients with 288 hepatic lesions included 202 malignant lesions and 86 benign lesions were assessed (confirmed by pathology or clinical follow‐up for 6 months). All patients underwent hepatic 3.0‐T MRI, including multi‐b DWI that used 12 b values. The ADC, D_p, D_t, perfusion fraction (f_p), α, and DDC values for normal liver, benign liver lesions, and malignant liver lesions were calculated. Independent sample t tests were used for comparisons. The diagnostic performance of the parameters was evaluated using ROC analysis. The AUC value for each model was also calculated. The value of D_p was significantly lower in benign lesions than in normal hepatic parenchyma while others were significantly higher (P < .001). Whereas Values of D_t and α in malignant hepatic lesions were significantly higher than in normal hepatic parenchyma (P < .001), and the D_p value was significantly lower (P < .001). Values of ADC, f_p, DDC, and α for malignant hepatic lesions were significantly lower than those for benign hepatic lesions (P < .001). ROC analysis showed that the diagnostic value of the biexponential model of normal hepatic parenchyma vs benign hepatic lesions and normal hepatic parenchyma vs malignant hepatic lesions was high (0.946 and 0.876, respectively). In the differential diagnosis of benign and malignant hepatic lesions, DDC had the highest AUC value (0.819). The biexponential and stretched‐exponential DWI may provide additional information and improve the differential diagnosis of benign and malignant hepatic lesions compared with the monoexponential DWI.