Preliminary Experience of 5.0 T Higher Field Abdominal Diffusion-Weighted MRI: Agreement of Apparent Diffusion Coefficient With 3.0 T Imaging

Reduced FOV T2-weighted imaging, 2.5D T2-weighted imaging, and high b-value diffusion-weighted imaging of the prostate at 5 T: a comparative study with 3 T

OBJECTIVES

To evaluate the image quality of prostate T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI) at 5 T.

METHODS

In this prospective study, asymptomatic adult male volunteers underwent conventional T2WI and multiple b-value DWI at both 3 T and 5 T, along with 2.5D T2WI at 5 T using the 2.5D imaging method. 2.5D imaging method improved in-plane resolution by reducing slice thickness and increasing the number of signal averaged to maintain the signal-to-noise ratio (SNR). Three scanning protocols were compared: conventional T2WI at 5 T vs. 3 T, 2.5D T2WI at 5 T vs. conventional T2WI at 5 T, and DWI at 5 T vs. 3 T. Quantitative analysis encompassed SNR, contrast-to-noise ratio (CNR), prostate dimensions, prostate volume (PV), edge rise distance of the dorsal prostate capsule, and ADC values in benign lesions. Image quality was qualitatively rated using a five-point Likert scale (1 = non-diagnostic, 5 = excellent). Statistical significance was assessed using paired t-test and Wilcoxon signed-rank test, with a significance threshold of P < 0.05.

RESULTS

Twenty participants were enrolled. Compared to 3 T, 5 T significantly increased SNR and CNR for T2WI (sagittal, coronal, and axial planes) and DWI (b-values of 1000, 1500, 2000 s/mm²) (P < 0.05). Image sharpness and clarity were significantly enhanced for T2WI and DWI at 5 T (P < 0.05). The 2.5D imaging method further improved T2WI resolution, overall image quality, and clarity of the prostate capsule. No significant differences were observed in artifact presence or PV between the T2WI groups (P > 0.05).

CONCLUSION

5 T bi-parametric MRI (bp-MRI) of the prostate demonstrated superior image quality.

Correlation between collateral compensation of the posterior cerebral artery on 5 T magnetic resonance imaging and clinical classifications in patients with Moyamoya angiopathy

PURPOSE

Various clinical classifications of Moyamoya angiopathy (MMA) have different characteristics of collateral compensation. Advancements in 5 T MRI have made it possible to non-invasively assess vascular collateralization using 4-dimensional MR angiography (4DMRA). The objective of this study is to analyze collateral compensation in MMA patients using 4DMRA and determine variations among different clinical classifications.

MATERIALS AND METHODS

Collateral compensation of posterior cerebral artery (PCA) to anterior circulation was evaluated using 4DMRA at 5 T MRI. After adjusting for confounding factors, multivariate analyses were conducted to compare the distribution of PCA collateral compensation among patients with different clinical classifications of MMA.

RESULTS

85 MMA patients were enrolled in the study. Among the 158 hemispheres evaluated, 100 were asymptomatic, 7 were hemorrhagic, 50 were ischemic, and 1 had a combination of hemorrhagic and ischemic stroke. Multivariate logistic regression analysis revealed a statistically significant difference in total PCA collateral compensation scores between asymptomatic and ischemic hemispheres (P < 0.001, 95% CI [0.614, 0.839]). Subgroup analysis revealed a clear distinction between asymptomatic hemispheres and ischemic hemispheres (P = 0.001, 95% CI [0.193, 0.677]) in terms of PCA compensation to middle cerebral artery through the parieto-occipital branch. However, no notable differences were observed in other compensation pathways.

CONCLUSION

The collateral compensation of PCA to the anterior circulation in MMA patients, assessed by 4DMRA at 5 T MRI, is significantly associated with ischemic MMA. The parieto-occipital branch may be the most important compensatory pathway. 4DMRA can potentially serve as a valuable tool for evaluating the risk of ischemic stroke in patients with MMA.

Quantification of the Proton Density Fat Fraction and Iron Content: A Comparative Study Between 3.0 T and 5.0 T MRI

BACKGROUND

Proton density fat fraction (PDFF) and R2* are noninvasive MRI biomarkers for quantifying fat and iron in abdominal organs. While 3.0 T MRI is widely used clinically, 5.0 T may offer improved accuracy and reliability. With the increasing availability of 5.0 T, assessing its feasibility and utility for quantifying PDFF and R2* in abdominal organs is needed.

PURPOSE

To determine the agreement of the PDFF and R2* in the liver, pancreas, kidney, and paraspinal muscle at 2 different field strengths.

STUDY TYPE

Prospective.

POPULATION

A total of 127 participants, including 60 healthy volunteers and 67 with metabolic dysfunction-associated steatotic liver disease (100 women and 27 men, 52 ± 9 years old).

FIELD STRENGTH/SEQUENCE

3.0 T and 5.0 T; Chemical shift-encoded multi-echo gradient echo sequence.

ASSESSMENT

PDFF and R2* values in the liver, pancreas, kidney, and paraspinal muscle were measured by three observers to evaluate the interobserver and interfield agreement using two 3.0 T scanners (scanner 1 and scanner 2) and one 5.0 T scanner.

STATISTICAL TESTS

Linear regression, Bland-Altman analyses, and intraclass correlation coefficients (ICCs). The p-value < 0.05 indicated statistically significant.

RESULTS

PDFF and R2* at 5.0 T were strongly correlated with those at two 3.0 T scanners for all organs (R2 = 0.905-0.998 for PDFF; 0.831-0.991 for R2*), indicating high interfield ICCs (0.892-0.993 for PDFF; 0.910-0.981 for R2*). Comparisons between 5.0 T and two 3.0 T scanners showed good interfield agreement for PDFF (mean bias, -0.57% to 0.03%) while a higher bias for R2* (mean bias, -16.53 to -2.64 s-1, 95% LoA, -34.28 to 1.21 s-1) at 5.0 T compared to the comparison between 3T scanners.

DATA CONCLUSION

5.0 T revealed high interfield agreement between the PDFF and R2* with 3.0 T, which could provide reliable quantification of fat and iron contents in abdominal organs.

EVIDENCE LEVEL

2.

TECHNICAL EFFICACY

Stage 2.

Analysis of the sample size used in clinical MRI studies

BACKGROUND

Choosing the sample size in clinical MRI studies is a common, important, and challenging task, complicated by the substantial variation in potential study parameters. However, considering previously used sample sizes may provide a reference point for future studies. The purpose of the study was to systematically investigate and to provide orientation for sample size selection based on information from current practices in clinical MRI studies.

METHODS

We assessed 1,046 research articles published in the Journal of Magnetic Resonance Imaging (JMRI) between 2020 and 2023. Only studies that involved patients were included. Review articles and studies using phantoms, animals, ex vivo samples, publicly available datasets, and non-imaging techniques (e.g., spectroscopy) were excluded. The included studies were categorized according to various criteria including anatomical region, field strength, contrast category (e.g., T1 mapping or diffusion-weighted imaging), retrospective vs. prospective and single vs. multicenter studies, automatic or manual segmentation, and quantitative or qualitative evaluations.

RESULTS

The median sample size (=number of patients) of the 734 studies included in the analysis was 74.5 (retrospective studies =  129, prospective studies =  41) and varied between the investigated categories. Sample size clusters were found in multiples of ten (e.g., 20, 30, 40), and 90.3% of the studies had less than 350 patients with 50.5% having less than 75, while 1.6% had more than 1,000 patients.

CONCLUSION

There is wide variation in the sample sizes of studies published by JMRI between 2020 and 2023, depending on study type, content category, or evaluation method. In clinical MRI studies, balancing statistical power and minimizing patient involvement is crucial, necessitating carefully choosing the sample size.

Magnetic resonance cholangiopancreatography at 5.0 T: quantitative and qualitative comparison with 3.0 T

BACKGROUND

This study aimed to assess the feasibility and performance of 5.0 T MRI in MR Cholangiopancreatography (MRCP) imaging compared to 3.0 T, focusing on detail visualization, signal-to-noise ratio (SNR), and image artifacts.

METHODS

A prospective study from May to October 2023 involved 20 healthy subjects and 19 with biliary dilation. Both groups underwent MRCP using 3.0 T and 5.0 T scanners. The detail visualization capability of the biliary tree and the SNR of the images were quantitatively evaluated. Two experienced MRI diagnostic physicians assessed the image artifacts qualitatively on a scale of 1 to 5. The t-test or Wilcoxon signed-rank test compared the quantitative results of biliary visualization and SNR between 3.0 T and 5.0 T scanners, while the Wilcoxon signed-rank test was used for comparing the level of image artifacts between the two scanners. The inter reader consistency was tested using Kappa test.

RESULTS

In both healthy subjects and those with biliary dilation, the 5.0 T group exhibited significantly higher numbers of biliary tree branches, along with greater total and maximum branch lengths, compared to the 3.0 T group (P<0.05). Although the maximum branch length was higher in the 5.0 T group among healthy subjects, this difference was not statistically significant (P = 0.053). No notable differences were observed in SNR and image artifact levels between the two groups across both field strengths (P>0.05).

CONCLUSIONS

MRCP at 5.0 T offers superior biliary tree visualization compared to 3.0 T. The performance regarding SNR and image artifacts between the two is relatively comparable.

Insulinoma detection and surgery planning: a comparative study of 5.0T MRI versus 3.0T MRI and MDCT

PURPOSE

To compare the ability among 5.0T MRI, 3.0T MRI and MDCT in identifying insulinomas and determining the tumor-to-duct relationship.

METHODS

A consecutive series of patients highly suspected of insulinomas were enrolled between October 2021 and February 2024, who underwent 5.0T MRI preoperatively, as well as 3.0T MRI or MDCT. The subjective and objective image quality, lesion-to-pancreas contrast, clarity of main pancreatic duct (MPD) and tumor-to-duct relationship at 5.0T, 3.0T MRI and MDCT were evaluated by three observers. The correlation between tumor-duct distance and clinically relevant postoperative pancreatic fistula (CR-POPF) risk was analyzed.

RESULTS

Forty patients (14 men; mean age, 46.4 ± 16.5 years) with insulinomas were included in this study. 21 of them underwent both 5.0T and 3.0T MRI; and 38 of them underwent 5.0T MRI and MDCT. The intra- and inter-observer agreement of 5.0T MRI were good to excellent. 5.0T showed significantly higher subjective and objective image quality on T1WI and DWI compared to 3.0T (p < 0.05). Lesion-to-pancreas contrast was superior across all sequences at 5.0T compared to 3.0T(p < 0.05). A head-to-head comparison of patients who received both 5.0T and 3.0T MRI demonstrated that tumor detection was superior with 5.0T MRI (5.0T: 100%; 3.0 T: 92.0%, p < 0.05). Feasibility of tumor-to-duct relationship assessment was superior at 5.0T, compared to 3.0T and MDCT (93.2%, 64.0% and 52.3%, respectively, p < 0.05). Tumor-duct distance could predict CR-POPF after enucleation surgery (areas under the ROC curve 0.79, p = 0.01).

CONCLUSION

5.0T MRI exhibits certain superiority in detecting insulinomas and assessing tumor-to-duct relationship compared to 3.0T MRI and MDCT.

Clinical Feasibility of 5.0 T MRI/MRCP in Characterizing Pancreatic Cystic Lesions: Comparison with 3.0 T and MDCT

Objectives: To assess the feasibility of 5.0 T magnetic resonance imaging (MRI) in characterizing pancreatic cystic lesions (PCLs), compared with 3.0 T MRI and multidetector computed tomography (MDCT). Methods: Thirty-five patients with PCLs underwent 5.0 T MR alongside 3.0 T MR or MDCT. Two observers measured subjective and objective image quality scores. The consistency of two observers between 5.0 T and 3.0 T was calculated by intraclass correlation coefficients. The characteristics of PCLs and their specific diagnosis, as well as benignity/malignancy, were evaluated across MDCT, 3.0 T, and 5.0 T MRI. Results: The 5.0 T MR demonstrated significantly higher subjective image quality and SNR on T1WI compared to that in 3.0 T MR (p < 0.05). The 5.0 T MRI identified more cyst lesions than the 3.0 T MRI (40 and 32) and MDCT (82 and 56). The sensitivity, specificity, and accuracy for differentiating benign from malignant lesions with 5.0 T MRI (75%, 100%, and 91.4%, respectively) surpassed those of 3.0 T MRI and MDCT. The accuracy of the specific diagnosis of PCLs at 5.0 T MRI (80%) was superior to 3.0 T MRI and MDCT. Conclusions: 5.0 T MRI exhibits certain superiority in delineating details of PCLs and in clinical diagnostic accuracy, outperforming MDCT and 3.0 T MRI while maintaining sufficient image quality.

Feasibility and Clinical Application of 5-T Noncontrast Dixon Whole-Heart Coronary MR Angiography: A Prospective Study

Background Coronary MR angiography (CMRA) at 3 T offers higher signal to noise ratio and contrast to noise ratio compared with 1.5 T. CMRA at 5 T may provide better diagnostic performance. Purpose To assess the feasibility and clinical application of 5-T noncontrast whole-heart CMRA and compare 5-T acquisition with 3-T acquisition. Materials and Methods From September 2023 to April 2024, patients scheduled for coronary CT angiography (CCTA) and volunteers were prospectively recruited. CCTA served as the reference standard in patients. CMRA was performed using a 3-T spectral attenuated inversion-recovery (3TSPAIR) sequence and 3-T Dixon (3TDixon) sequence with routine spatial resolution (3TSPAIR-routine and 3TDixon-routine, respectively), and 5-T Dixon (5TDixon) with routine and high spatial resolution (5TDixon-routine and 5TDixon-high, respectively). The study evaluated image quality, coronary artery calcium (CAC), the severity of coronary artery disease (CAD) graded according to Coronary Artery Disease Reporting and Data System, and the presence of ≥50% coronary stenosis. The nonparametric paired Wilcoxon signed rank test, McNemar test, generalized estimating equation model, and kappa test were used. Results Eight volunteers and 79 patients were included (mean age, 52 years ± 11 [SD]; 48 male). Image quality was higher for 5TDixon-routine compared with 3TSPAIR-routine and 3TDixon-routine (P < .001 for both) and similar for 5TDixon-high (P = .60). The per-segment sensitivity for CAC was higher at 5TDixon-high than 5TDixon-routine (78.3% vs 53.3%; P < .001), with no difference in specificity (98.6% vs 98.6%; P > .99). In grading the severity of CAD, 5TDixon-routine showed better consistency with CCTA than 3TSPAIR-routine (κ = 0.46 vs 0.13) and 3TDixon-routine (κ = 0.55 vs 0.42). For detecting ≥50% stenosis, the per-patient sensitivity, specificity, and accuracy were as follows: 5TDixon-routine versus 3TSPAIR-routine, 88.9% versus 55.6%, 86.5% versus 62.2%, and 87.0% versus 60.9% (P = .55, .01, and .18, respectively); 5TDixon-routine versus 3TDixon-routine, 90.0% versus 80.0%, 86.8% versus 71.1%, and 87.5% versus 72.9%, respectively (P > .05 for all). Conclusion Noncontrast CMRA at 5 T shows potential to evaluate CAC and coronary stenosis simultaneously and demonstrates superior diagnostic performance compared with at 3 T. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Rahsepar and Kim in this issue.

Application of 5T glutamate chemical exchange saturation transfer imaging in brain tumors: preliminary results

PURPOSE

Glutamate chemical exchange saturation transfer (GluCEST) is a non-invasive CEST imaging technique for detecting glutamate levels in tissues. We aimed to investigate the reproducibility of the 5T GluCEST technique in healthy volunteers and preliminarily explore its potential clinical application in patients with brain tumors.

METHODS

Ten volunteers (4 males, mean age 29 years) underwent three 5T GluCEST imaging scans. The reproducibility of the three imaging GluCEST measurements was assessed using one-way repeated measures analysis of variance (ANOVA), generalized estimating equations, and linear mixed models. Twenty-eight patients with brain tumors (10 males, mean age 54 years) underwent a single GluCEST scan preoperatively, and t-tests were used to compare the differences in GluCEST values between different brain tumors. In addition, the diagnostic accuracy of GluCEST values in differentiating brain tumors was assessed using the receiver work characteristics (ROC) curve.

RESULTS

The coefficients of variation of GluCEST values in healthy volunteers were less than 5% for intra-day, inter-day, and within-subjects and less than 10% for between-subjects. High-grade gliomas (HGG) had higher GluCEST values compared to low-grade gliomas (LGG) (P < 0.001). In addition, cerebellopontine angle (CPA) meningiomas had higher GluCEST values than acoustic neuromas (P < 0.001). The area under the curve (AUC) of the GluCEST value for differentiating CPA meningioma from acoustic neuroma was 0.93.

CONCLUSION

5T GluCEST images are highly reproducible in healthy brains. In addition, the 5T GluCEST technique has potential clinical applications in differentiating LGG from HGG and CPA meningiomas from acoustic neuromas.

Detecting microvascular invasion in hepatocellular carcinoma using the impeded diffusion fraction technique to sense macromolecular coordinated water

OBJECTIVES

Impeded diffusion fraction (IDF) is a novel and promising diffusion-weighted imaging (DWI) technique that allows for the detection of various diffusion compartments, including macromolecular coordinated water, free diffusion, perfusion, and cellular free water. This study aims to investigate the clinical potential of IDF-DWI in detecting microvascular invasion (MVI) in hepatocellular carcinoma (HCC).

METHODS

66 patients were prospectively included. Metrics derived from IDF-DWI and the apparent diffusion coefficient (ADC) were calculated. Multivariate logistic regression was employed to identify clinical risk factors. Diagnostic performance was evaluated using the area under the receiver operating characteristics curve (AUC-ROC), the area under the precision-recall curve (AUC-PR), and the calibration error (cal-error). Additionally, a power analysis was conducted to determine the required sample size.

RESULTS

The results suggested a significantly higher fraction of impeded diffusion (FID) originating from IDF-DWI in MVI-positive HCCs (p < 0.001). Moreover, the ADC was found to be significantly lower in MVI-positive HCCs (p = 0.019). Independent risk factors of MVI included larger tumor size and elevated alpha-fetoprotein (AFP) levels. The nomogram model incorporating ADC, FID, tumor size, and AFP level yielded the highest diagnostic accuracy for MVI (AUC-PR = 0.804, AUC-ROC = 0.783, cal-error = 0.044), followed by FID (AUC-PR = 0.693, AUC-ROC = 0.760, cal-error = 0.060) and ADC (AUC-PR = 0.570, AUC-ROC = 0.651, cal-error = 0.164).

CONCLUSION

IDF-DWI shows great potential in noninvasively, accurately, and preoperatively detecting MVI in HCC and may offer clinical benefits for prognostic prediction and determination of treatment strategy.

Improved Detection of Target Metabolites in Brain Tumors with Intermediate TE, High SNR, and High Bandwidth Spin-Echo Sequence at 5T

BACKGROUND AND PURPOSE

Due to high chemical shift displacement, challenges emerge at ultra-high fields when measuring metabolites using 1H-MRS. Our goal was to investigate how well the high SNR and high bandwidth spin-echo (HISE) technique perform at 5T for detecting target metabolites in brain tumors.

MATERIALS AND METHODS

Twenty-six subjects suspected of having brain tumors were enrolled. HISE and point-resolved spectroscopy (PRESS) single-voxel spectroscopy scans were collected with a 5T clinical scanner with an intermediate TE (TE = 144 ms). The main metabolites, including total NAA, Cr, and total Cho, were accessed and compared between HISE and PRESS using a paired Student t test, with full width at half maximum and SNR as covariates. The detection rate of specific metabolites, including lactate, alanine, and lipid, and subjective spectral quality were accessed and compared between HISE and PRESS.

RESULTS

Twenty-three pathologically confirmed brain tumors were included. Only the full width at half maximum for total NAA was significantly lower with HISE than with PRESS (P < .05). HISE showed a significantly higher SNR for total NAA, Cr, and total Cho compared with PRESS (P < .05). Lactate was detected in 21 of the 23 cases using HISE, but in only 4 cases using PRESS. HISE detected alanine in 8 of 9 meningiomas, whereas PRESS detected alanine in just 3 meningiomas. PRESS found lipid in more cases than HISE, while HISE outperformed PRESS in terms of subjective spectral quality.

CONCLUSIONS

HISE outperformed the clinical standard PRESS technique in detecting target metabolites of brain tumors at 5T, particularly lactate and alanine.

Preoperative Grading of Rectal Cancer with Multiple DWI Models, DWI-Derived Biological Markers, and Machine Learning Classifiers

Background: this study aimed to utilize various diffusion-weighted imaging (DWI) techniques, including mono-exponential DWI, intravoxel incoherent motion (IVIM), and diffusion kurtosis imaging (DKI), for the preoperative grading of rectal cancer. Methods: 85 patients with rectal cancer were enrolled in this study. Mann-Whitney U tests or independent Student's t-tests were conducted to identify DWI-derived parameters that exhibited significant differences. Spearman or Pearson correlation tests were performed to assess the relationships among different DWI-derived biological markers. Subsequently, four machine learning classifier-based models were trained using various DWI-derived parameters as input features. Finally, diagnostic performance was evaluated using ROC analysis with 5-fold cross-validation. Results: With the exception of the pseudo-diffusion coefficient (Dp), IVIM-derived and DKI-derived parameters all demonstrated significant differences between low-grade and high-grade rectal cancer. The logistic regression-based machine learning classifier yielded the most favorable diagnostic efficacy (AUC: 0.902, 95% Confidence Interval: 0.754-1.000; Specificity: 0.856; Sensitivity: 0.925; Youden Index: 0.781). Conclusions: utilizing multiple DWI-derived biological markers in conjunction with a strategy employing multiple machine learning classifiers proves valuable for the noninvasive grading of rectal cancer.

Higher field reduced FOV diffusion-weighted imaging for abdominal imaging at 5.0 Tesla: image quality evaluation compared with 3.0 Tesla

OBJECTIVE

To evaluate the image quality of reduced field-of-view (rFOV) DWI for abdominal imaging at 5.0 Tesla (T) compared with 3.0 T.

METHODS

Fifteen volunteers were included into this prospective study. All the subjects underwent the 3.0 T and 5.0 T MR examinations (time interval: 2 ± 1.9 days). Free-breathing (FB), respiratory-triggered (RT), and navigator-triggered (NT) spin-echo echo-planner imaging-based rFOV-DWI examinations were conducted at 3.0 T and 5.0 T (FB3.0 T, NT3.0 T, RT3.0 T, FB5.0 T, NT5.0 T, and RT5.0 T) with two b values (b = 0 and 800 s/mm2), respectively. The signal-to-noise ratio (SNR) of different acquisition approaches were determined and statistically compared. The image quality was assessed and statistically compared with a 5-point scoring system.

RESULTS

The SNRs of any 5.0 T DWI images were significantly higher than those of any 3.0 T DWI images for same anatomic locations. Moreover, 5.0 T rFOV-DWIs had the significantly higher sharpness scores than 3.0 T rFOV-DWIs. Similar distortion scores were observed at both 3.0 T and 5.0 T. Finally, RT5.0 T displayed the best overall image quality followed by NT5.0 T, FB5.0 T, RT3.0 T, NT3.0 T and FB3.0 T (RT5.0 T = 3.9 ± 0.3, NT5.0 T = 3.8 ± 0.3, FB5.0 T = 3.4 ± 0.3, RT3.0 T = 3.2 ± 0.4, NT3.0 T = 3.1 ± 0.4, and FB3.0 T = 2.7 ± 0.4, p < 0.001).

CONCLUSION

The 5.0 T rFOV-DWI showed better overall image quality and improved SNR compared to 3.0 T rFOV-DWI, which holds clinical potential for identifying the abdominal abnormalities in routine practice.

CRITICAL RELEVANCE STATEMENT

This study provided evidence that abdominal 5.0 Tesla reduced field of view diffusion-weighted imaging (5.0 T rFOV-DWI) exhibited enhanced image quality and higher SNR compared to its 3.0 Tesla counterparts, holding clinical promise for accurately visualizing abdominal abnormalities.

KEY POINTS

• rFOV-DWI was firstly integrated with high-field-MRI for visualizing various abdominal organs. • This study indicated the feasibility of abdominal 5.0 T-rFOV-DWI. • Better image quality was identified for 5.0 T rFOV-DWI.

The Feasibility of Using Tri-Exponential Intra-Voxel Incoherent Motion DWI for Identifying the Microvascular Invasion in Hepatocellular Carcinoma

Purpose

To assess the effectiveness of tri-exponential Intra-Voxel Incoherent Motion (tri-IVIM) MRI in preoperatively identifying microvascular invasion (MVI) in hepatocellular carcinoma (HCC).

Patients and Methods

In this prospective study, 67 patients with HCC were included. Metrics from bi-exponential IVIM (bi-IVIM) and tri-IVIM were calculated. Subgroup comparisons were analyzed using the independent Student's t-test or Mann-Whitney U-test. Logistic regression was performed to explore clinical risk factors. Diagnostic performance was assessed using receiver operating characteristic (ROC) curves, calibration curves and decision curve analysis.

Results

MVI-positive HCCs exhibited significantly lower true diffusion coefficient (Dt) from bi-IVIM, as well as fast-diffusion coefficients (Df) and slow-diffusion coefficients (Ds) from tri-IVIM, compared to MVI-negative HCCs (p < 0.05). Tumor size and alpha-fetoprotein (AFP) were identified as risk factors. The combination of tri-IVIM-derived metrics (Ds and Df) yielded higher diagnostic accuracy (AUC = 0.808) compared to bi-IVIM (AUC = 0.741). A predictive model based on a nomogram was constructed using Ds, Df, tumor size, and AFP, resulting in the highest diagnostic accuracy (AUC = 0.859). Decision curve analysis indicated that the constructed model, provided the highest net benefit by accurately stratifying the risk of MVI, followed by tri-IVIM and bi-IVIM.

Conclusion

Tri-IVIM can provide information on perfusion and diffusion for evaluating MVI in HCC. Additionally, tri-IVIM outperformed bi-IVIM in identifying MVI-positive HCC. By integrating clinical risk factors and metrics from tri-IVIM, a predictive nomogram exhibited the highest diagnostic accuracy, potentially aiding in the noninvasive and preoperative assessment of MVI.

Stability and repeatability of diffusion-weighted imaging (DWI) of normal pancreas on 5.0 Tesla magnetic resonance imaging (MRI)

To explore the stability and repeatability of diffusion-weighted imaging (DWI) of normal pancreas with different field of views (FOV) on 5.0 T magnetic resonance imaging (MRI) system. Twenty healthy subjects underwent two sessions of large FOV (lFOV) and reduced FOV (rFOV) DWI sequence scanning. Two radiologists measured the apparent diffusion coefficient (ADC) values and the signal-to-noise ratio (SNR) of the pancreatic head, body, and tail on DWI images, simultaneously, using a 5-point scale, evaluate the artifacts and image quality. One radiologist re-measured the ADC on DWI images again after a 4-week interval. The test-retest repeatability of two scan sessions were also evaluated. Intra-observer and inter-observer at lFOV and rFOV, the ADC values were not significantly different (P > 0.05), intraclass correlation coefficients (ICCs) and coefficient of variations were excellence (ICCs 0.85-0.99, CVs < 8.0%). The ADC values were lower with rFOV than lFOV DWI for the head, body, tail, and overall pancreas. The consistency of the two scan sessions were high. The high stability and repeatability of pancreas DWI has been confirmed at 5.0 T. Scan durations are reduced while resolution and image quality are improved with rFOV DWI, which is more preferable than lFOV for routine pancreas imaging.

T2-weighted MRI and reduced-FOV diffusion-weighted imaging of the human pancreas at 5 T: A comparison study with 3 T

PURPOSE

The purpose of this study was to explore the feasibility of pancreatic imaging at 5 T and evaluate the practical improvement of T2-weighted MRI and diffusion-weighted imaging (DWI) at 5 T as compared with 3 T.

METHODS

Eighteen healthy subjects were recruited for this pilot study. MRI examinations were performed using 3 and 5 T scanners. MRI sequences included T2-weighted fast spin-echo and DWI with reduced field-of-view. Subjective image analysis using a four-point Likert scale was performed by two experienced radiologists. The SNR, contrast ratio, and apparent diffusion coefficient (ADC) were measured in the pancreatic head, body, and tail. The coefficient of variation (CV) of the ADC was calculated. A series of paired Wilcoxon tests were used to compare the subjective image quality, mean ADC value, and CV of ADC between the 3 and 5 T measurements. p <0.05 was considered statistically significant.

RESULTS

For T2-weighted images, there were no significant differences in image quality ratings between 3 and 5 T. On DWI images (b = 0 and 800 s/mm² ), the image quality ratings were significantly higher at 5 T than at 3 T. The SNRs of both T2-weighted and DWI images were significantly higher at 5 T. There was no significant difference in the mean ADC values and CV of ADC between 3 and 5 T.

CONCLUSION

This initial study proved that 5 T MRI can be used to acquire pancreatic images with higher SNR and sufficient image quality compared to 3 T MRI.

Time-of-Flight Intracranial MRA at 3 T versus 5 T versus 7 T: Visualization of Distal Small Cerebral Arteries

Background Three-dimensional (3D) time-of-flight (TOF) MR angiography (MRA) at 7 T has been reported to have high image quality for visualizing small perforating vessels. However, B₁ inhomogeneity and more physiologic considerations limit its applications. Angiography at 5 T may provide another choice for intracranial vascular imaging. Purpose To evaluate the image quality and cerebrovascular visualization of 5-T 3D TOF MRA for visualizing intracranial small branch arteries. Materials and Methods Participants (healthy volunteers or participants with a history of ischemic stroke undergoing intracranial CT angiography or MRA for identifying steno-occlusive disease) were prospectively included from September 2021 to November 2021. Each participant underwent 3-T, 5-T, and 7-T 3D TOF MRA with use of customized MR protocols within 48 hours. Radiologist scoring from 0 (invisible) to 3 (excellent) and quantitative assessment were obtained to evaluate the image quality. The Friedman test was used for comparison of characteristics derived from 3 T, 5 T, and 7 T. Results A total of 12 participants (mean age ± SD, 38 years ± 9; nine men) were included. Visualizations of the distal arteries and small vessels at 5-T TOF MRA were significantly higher than those at 3 T (median score: 3.0 vs 2.0, all P < .001 for distal segments and lenticulostriate artery; median score: 2.0 vs 0, P < .001 for pontine artery). The total length of small vessel branches detected at 5 T was larger than that at 3 T (5.1 m ± 0.7 vs 1.9 m ± 0.4; P < .001). However, there was no evidence of a significant difference compared with 7 T in either the depiction of distal segments and small vessel branches (average median score, 2.5; all P > .05) or the quantitative measurements (total length, 5.6 m ± 0.5; P = .41). Conclusion Three-dimensional time-of-flight MR angiography at 5 T presented the capability to provide superior visualization of distal large arteries and small vessel branches (in terms of subjective and quantitative assessment) to 3 T and had image quality similar to 7 T. © RSNA, 2022 Online supplemental material is available for this article. An earlier incorrect version appeared online. This article was corrected on September 14, 2022.

Renal imaging at 5 T versus 3 T: a comparison study

Background

Recently, a whole-body 5 T MRI scanner was developed to open the door of abdominal imaging at high-field strength. This prospective study aimed to evaluate the feasibility of renal imaging at 5 T and compare the image quality, potential artifacts, and contrast ratios with 3 T.

Methods

Forty healthy volunteers underwent MRI examination both at 3 T and 5 T. MRI sequences included T1-weighted gradient-echo (GRE), T2-weighted fast spin echo, diffusion-weighted imaging, and multi-echo GRE T2* mapping. Image quality and presence of artifacts were assessed for all sequences using four-point scales. For anatomical imaging, the signal-to-noise ratio (SNR) and contrast ratio (CR) of abdomen organ tissues were calculated. Besides, for functional imaging, the contrast-to-noise ratio of cortex/medulla was calculated. Wilcoxon signed rank-sum test was used to compare the visual evaluation scores and quantitative measurements between 3 and 5 T images.

Results

Compared to 3 T examination, T1-weighted sequence at 5 T showed significantly better image quality with higher conspicuity of the renal veins and arteries, and comparable artifacts. Image quality was comparable between both field strengths on T2-weighted images, whereas a significantly higher level of artifacts was observed at 5 T. Besides, 5 T MRI contributed to higher SNR and CR for abdomen organ tissues. For functional imaging, 5 T MRI showed improved corticomedullar discrimination. There was no significant difference between apparent diffusion coefficient of renal at 3 T and 5 T, while 5 T MRI resulted in significantly shorter T2* values in both cortex and medulla.

Conclusions

5 T MRI provides anatomical and functional images of the kidney with sufficient image quality.

Application of medical imaging methods and artificial intelligence in tissue engineering and organ-on-a-chip

Organ-on-a-chip (OOC) is a new type of biochip technology. Various types of OOC systems have been developed rapidly in the past decade and found important applications in drug screening and precision medicine. However, due to the complexity in the structure of both the chip-body itself and the engineered-tissue inside, the imaging and analysis of OOC have still been a big challenge for biomedical researchers. Considering that medical imaging is moving towards higher spatial and temporal resolution and has more applications in tissue engineering, this paper aims to review medical imaging methods, including CT, micro-CT, MRI, small animal MRI, and OCT, and introduces the application of 3D printing in tissue engineering and OOC in which medical imaging plays an important role. The achievements of medical imaging assisted tissue engineering are reviewed, and the potential applications of medical imaging in organoids and OOC are discussed. Moreover, artificial intelligence - especially deep learning - has demonstrated its excellence in the analysis of medical imaging; we will also present the application of artificial intelligence in the image analysis of 3D tissues, especially for organoids developed in novel OOC systems.