Simultaneous Multislice Diffusion-weighted Imaging Research Articles

Evaluation of simultaneous multi-slice acquisition with advanced processing for free-breathing diffusion-weighted imaging in patients with liver metastasis

ObjectivesDiffusion-weighted imaging (DWI) with simultaneous multi-slice (SMS) acquisition and advanced processing can accelerate acquisition time and improve MR image quality. This study evaluated the image quality and apparent diffusion coefficient (ADC) measurements of free-breathing DWI acquired from patients with liver metastases using a prototype SMS-DWI acquisition (with/without an advanced processing option) and conventional DWI.MethodsFour DWI schemes were compared in a pilot 5-patient cohort; three DWI schemes were further assessed in a 24-patient cohort. Two readers scored image quality of all b-value images and ADC maps across the three methods. ADC measurements were performed, for all three methods, in left and right liver parenchyma, spleen, and liver metastases. The Friedman non-parametric test (post-hoc Wilcoxon test with Bonferroni correction) was used to compare image quality scoring; t-test was used for ADC comparisons.ResultsSMS-DWI was faster (by 24%) than conventional DWI. Both readers scored the SMS-DWI with advanced processing as having the best image quality for highest b-value images (b750) and ADC maps; Cohen’s kappa inter-reader agreement was 0.6 for b750 image and 0.56 for ADC maps. The prototype SMS-DWI sequence with advanced processing allowed a better visualization of the left lobe of the liver. ADC measured in liver parenchyma, spleen, and liver metastases using the SMS-DWI with advanced processing option showed lower values than those derived from the SMS-DWI method alone (t-test, p < 0.0001; p < 0.0001; p = 0.002).ConclusionsFree-breathing SMS-DWI with advanced processing was faster and demonstrated better image quality versus a conventional DWI protocol in liver patients.Clinical relevance statementFree-breathing simultaneous multi-slice- diffusion-weighted imaging (DWI) with advanced processing was faster and demonstrated better image quality versus a conventional DWI protocol in liver patients.Key Points• Diffusion-weighted imaging (DWI) with simultaneous multi-slice (SMS) can accelerate acquisition time and improve image quality.• Apparent diffusion coefficients (ADC) measured in liver parenchyma, spleen, and liver metastases using the simultaneous multi-slice DWI with advanced processing were significantly lower than those derived from the simultaneous multi-slice DWI method alone.• Simultaneous multi-slice DWI sequence with inline advanced processing was faster and demonstrated better image quality in liver patients.

Abdominal Diffusion-Weighted MRI With Simultaneous Multi-Slice Acquisition: Agreement and Reproducibility of Apparent Diffusion Coefficients Measurements.

Simultaneous multi-slice diffusion-weighted imaging (SMS-DWI) can shorten acquisition time in abdominal imaging. To investigate the agreement and reproducibility of apparent diffusion coefficient (ADC) from abdominal SMS-DWI acquired with different vendors and different breathing schemes. Prospective. Twenty volunteers and 10 patients. 3.0 T, SMS-DWI with a diffusion-weighted echo-planar imaging sequence. SMS-DWI was acquired using breath-hold and free-breathing techniques in scanners from two vendors, yielding four scans in each participant. Average ADC values were measured in the liver, pancreas, spleen, and both kidneys. Non-normalized ADC and ADCs normalized to the spleen were compared between vendors and breathing schemes. Paired t-test or Wilcoxon signed rank test; intraclass correlation coefficient (ICC); Bland-Altman method; coefficient of variation (CV) analysis; significance level: P < 0.05. Non-normalized ADCs from the four SMS-DWI scans did not differ significantly in the spleen (P = 0.262, 0.330, 0.166, 0.122), right kidney (P = 0.167, 0.538, 0.957, 0.086), and left kidney (P = 0.182, 0.281, 0.504, 0.405), but there were significant differences in the liver and pancreas. For normalized ADCs, there were no significant differences in the liver (P = 0.315, 0.915, 0.198, 0.799), spleen (P = 0.815, 0.689, 0.347, 0.423), pancreas (P = 0.165, 0.336, 0.304, 0.584), right kidney (P = 0.165, 0.336, 0.304, 0.584), and left kidney (P = 0.496, 0.304, 0.443, 0.371). Inter-reader agreements of non-normalized ADCs were good to excellent (ICCs ranged from 0.861 to 0.983), and agreement and reproducibility were good to excellent depending on anatomic location (CVs ranged from 3.55% to 13.98%). Overall CVs for abdominal ADCs from the four scans were 6.25%, 7.62%, 7.08, and 7.60%. The normalized ADCs from abdominal SMS-DWI may be comparable between different vendors and breathing schemes, showing good agreement and reproducibility. ADC changes above approximately 8% may potentially be considered as a reliable quantitative biomarker to assess disease or treatment-related changes. 2 TECHNICAL EFFICACY: Stage 2.

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

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

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

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. 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. We included 33 children and adolescents (12 female, 21 male; mean age 10±5years) 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 ≥5mm. All statistical analysis was performed using Stata/SE v15.1. Simultaneous multi-slice DWI ADC values were slightly lower compared to standard echoplanar DWI for both renal cysts and angiomyolipomas (mean difference 0.05×10-3mm2/s, 95% confidence interval [CI] 0.40-0.50 and 0.024×10-3mm2/s, 95% CI 0.17-0.21, respectively, with P>0.1). Our results showed that renal lesions with ADC values >1.69×10-3mm2/s were all cysts, whereas lesions with values <1.16×10-3mm2/s were all angiomyolipomas. However, ADC values could not discriminate between lipid-rich and lipid-poor angiomyolipomas (P>0.1, for both sequences). 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.

Coil-combined split slice-GRAPPA for simultaneous multi-slice diffusion MRI

Objective: To develop a kernel optimization method called coil-combined split slice-GRAPPA (CC-SSG) to improve the accuracy of the reconstructed coil-combined images for simultaneous multi-slice (SMS) diffusion weighted imaging (DWI) data.Methods: The CC-SSG method optimizes the tuning parameters in the k-space SSG kernels to achieve an optimal trade-off between the intra-slice artifact and inter-slice leakage after the root-sum-of-squares (rSOS) coil combining of the de-aliased SMS DWI data. A detailed analysis is conducted to evaluate the contributions of the intra-slice artifact and inter-slice leakage to the total reconstruction error after coil combining.Results: Comparisons of the proposed CC-SSG method with the slice-GRAPPA (SG) and split slice-GRAPPA (SSG) methods are provided using two in-vivo readout-segmented (RS) EPI datasets collected from stroke patients. The CC-SSG method demonstrates improved accuracy of the reconstructed coil-combined images and the estimated diffusion tensor imaging (DTI) maps.Conclusion: CC-SSG strikes a good balance between the intra-slice artifact and inter-slice leakage for rSOS coil combining, and so can yield better reconstruction performance compared to SG and SSG for rSOS reconstruction. The optimal trade-off between the two artifacts is robust to the contrast of SMS data and the choice of the coil combining method.

Diffusion-weighted imaging of the kidney: comparison between simultaneous multi-slice and integrated slice-by-slice shimming echo planar sequence

To compare the simultaneous multi-slice (SMS) and integrated slice-by-slice shimming (iShim) single-shot echo planar imaging (ssEPI) for diffusion-weighted imaging (DWI) of the kidneys. In this prospective study, six healthy volunteers and 22 patients with renal diseases underwent SMS and iShim DWI of the kidney with five b-values (0, 80, 400, 800, 1,600 s/mm2) at 3 T. The subjective image quality, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and ADC values were evaluated. The subjective image quality scores, SNR, CNR, ADC values and scan time of SMS and iShim DWI were compared. Scan time of SMS DWI (1 minute 38 seconds) was significantly reduced compared to iShim ssEPI (3 minutes 33 seconds). No statistically significant differences in the SNR or subjective image quality were observed on the b=0 images, but the SNR and overall image quality scores were significantly higher on the other four b-value images at SMS DWI. Image distortions were also comparable, but there were fewer artefacts on the b=80 and b=800 images in SMS DWI. CNR was significantly higher on the b=0 and b=1,600 images in SMS DWI. SNR and subjective image-quality scores of ADC maps were significantly higher in SMS DWI, whereas CNR showed no significant difference. The ADC value of renal parenchyma was similar in SMS and iShim DWI (1.54±0.11 × 10-3 versus 1.52±0.16×10-3 mm2/s, p=0.343). SMS can substantially reduce imaging time of kidney DWI with slightly improved image quality and comparable ADC values of renal parenchyma compared to iShim ss-EPI sequence.

Simultaneous Multislice Diffusion-Weighted Imaging of the Kidney: A Systematic Analysis of Image Quality.

The aims of this study were to implement a protocol for simultaneous multislice (SMS) accelerated diffusion-weighted imaging (DWI) of the kidneys and to perform a systematic analysis of image quality of the data sets. Ten healthy subjects and 5 patients with renal masses underwent DWI of the kidney in this prospective institutional review board-approved study on a 3 T magnetic resonance scanner. Simultaneous multislice DWI echo-planar sequences (acceleration factors [AFs] 2 and 3) were compared with conventional echo-planar DWI as reference standard for each acquisition scheme. The following 3 acquisition schemes were applied: comparison A, with increased number of acquisitions at constant scan time; comparison B, with reduction of acquisition time; and comparison C, with increased slice resolution (constant acquisition time, increasing number of slices). Interreader reliability was analyzed by calculating the intraclass correlation coefficient (ICC). Qualitative image quality features were evaluated by 2 independent radiologists on a 5-point Likert scale. Quantification accuracy of the apparent diffusion coefficients (ADCs) and signal-to-noise ratios (SNRs) were assessed by region of interest analysis. Furthermore, lesion conspicuity in the 5 patients was assessed using a 5-point Likert scale by 2 independent radiologists. Interreader agreement was substantial with an ICC of 0.68 for the overall image quality and an ICC of 0.73 for the analysis of artifacts. In comparison A, AF2 resulted in increased SNR (P < 0.05) by 21% at stable image quality scores (image quality: P = 0.76, artifacts: P = 0.21). In comparison B, applying AF2, the scan time could be reduced by 46% without significant reduction in qualitative image quality scores (P = 0.059) or SNR (P = 0.126). In comparison C, slice resolution could be improved by 28% using AF2 with stable image quality scores and SNR. In general, AF3 resulted in reduced image quality and SNR. Significantly reduced ADC values were observed for AF3 in comparison C (cortex: P = 0.003; medulla: P = 0.001) compared with the standard echo-planar imaging sequence. The conventional DWI and the SMS DWI with AF2 showed stable lesion conspicuity ([AF1/AF2]: reader 1 [1.8/1.4] and reader 2 [1.8/1.4]). The lesion conspicuity was lower using AF3 (reader 1: 2.2 and reader 2: 1.8). In conclusion, SMS DWI of the kidney is a potential tool to substantially reduce scan time without negative effects on SNR, ADC quantification accuracy, and image quality if an AF2 is used. Although AF3 results in even higher scan time reduction, a negative impact on image quality, SNR, ADC quantification accuracy, and lesion conspicuity must be considered.

Feasibility of accelerated simultaneous multislice diffusion-weighted MRI of the prostate.

To assess the feasibility of simultaneous multislice (SMS) single-shot echo-planar-imaging (EPI) for accelerated diffusion-weighted imaging (DWI) of the prostate. For phantom measurements a dedicated DWI phantom with different sucrose concentrations was used. In addition, 10 volunteers and 16 patients with suspected prostate cancer were examined for in vivo measurements. All examinations were performed with a 3T magnetic resonance imaging (MRI) system. A prototype simultaneous multislice EPI sequence (DW-EPISMS ; acquisition time 3:14 min) was acquired and compared to a single-shot EPI sequence (DW-EPISS ; acquisition time 6:12 min) serving as a standard of reference. Different image quality parameters of EPISMS were assessed qualitatively (overall image quality, anatomic differentiability, lesion conspicuity, image noise, distortion; two independent readers; 5-point Likert-scale [5 = excellent]) and quantitatively (ADC-values by calculating interclass correlation [ICC] and Bland-Altman limits of agreement [LoA] as measures for reproducibility) and compared to DW-EPISS . DW-EPISMS allowed for a substantially reduced acquisition time as compared to DW-EPISS (˜50%). Bland-Altman plots revealed robust measurement repeatability for DW-EPISMS in the phantom study. Overall image quality did not significantly differ between DW-EPISMS and DW-EPISS (b1500 images P = 0.5; ADC maps P = 0.7). Only in b1500 DW images was subjective image noise rated significantly higher in DW-EPISS than in DW-EPISMS (P = 0.006). Quantitative analysis of ADC-values revealed not significant differences between DW-EPISMS and DW-EPISS (P = 0.7) and high measures for reproducibility ICC ≥0.96. Simultaneous multislice DWI is feasible for accelerated prostate MRI allowing for a substantially reduced examination time with similar image quality and ADC-values as compared to a standard of reference DWI sequence. 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1507-1515.

Segmented simultaneous multi-slice diffusion weighted imaging with generalized trajectories.

The purpose of this work is to develop and evaluate a single framework for the use of Cartesian and non-Cartesian segmented trajectories for rapid and robust simultaneous multislice (SMS) diffusion weighted imaging (DWI) at 3 Telsa (T). A generalized SMS approach with intrinsic phase navigation using Multiplexed Sensitivity Encoding (MUSE) was developed. Segmented blipped-controlled aliasing in parallel imaging echo planar imaging (EPI) and z-gradient modulated spiral trajectories were examined using SMS DWI scans at 3T with a 32-channel head coil. The generalized SMS MUSE reconstruction framework was successful in significantly reducing artifacts for all trajectories. A DWI brain volume with a 67.5-mm height, 1.5-mm isotropic resolution, and 90 diffusion weightings was obtained in a scan time of 6 minutes. The MUSE technique can be generalized to allow for reconstruction of both Cartesian and non-Cartesian segmented trajectories. Magn Reson Med 78:1476-1481, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

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

PurposeTo optimize and test a diffusion-weighted imaging (DWI) echo-planar imaging (EPI) sequence with simultaneous multi-slice (SMS) excitation in the liver and pancreas regarding acquisition time (TA), number of slices, signal-to-noise ratio (SNR), image quality (IQ), apparent diffusion coefficient (ADC) quantitation accuracy, and feasibility of intravoxel incoherent motion (IVIM) analysis. Materials and methodsTen healthy volunteers underwent DWI of the upper abdomen at 3T. A SMS DWI sequence with CAIPIRINHA unaliasing technique (acceleration factors 2/3, denoted AF2/3) was compared to standard DWI-EPI (AF1). Four schemes were evaluated: (i) reducing TA, (ii) keeping TA identical with increasing number of averages, (iii) increasing number of slices with identical TA (iv) increasing number of b-values for IVIM. Acquisition schemes i-iii were evaluated qualitatively (reader score) and quantitatively (ADC values, SNR). ResultsIn scheme (i) no differences in SNR were observed (p=0.321−0.038) with reduced TA (AF2 increase in SNR/time 75.6%, AF3 increase SNR/time 102.4%). No SNR improvement was obtained in scheme (ii). Increased SNR/time could be invested in acquisition of more and thinner slices or higher number of b-values. Image quality scores were stable for AF2 but decreased for AF3. Only for AF3, liver ADC values were systematically lower. ConclusionSMS-DWI of the liver and pancreas provides substantially higher SNR/time, which either may be used for shorter scan time, higher slice resolution or IVIM measurements.