Enhanced parameter estimation in multiparametric arterial spin labeling using artificial neural networks.

PURPOSE: Multiparametric arterial spin labeling (MP-ASL) can quantify cerebral blood flow (CBF) and arterial cerebral blood volume (CBVa). However, its accuracy is compromised owing to its intrinsically low SNR, necessitating complex and time-consuming parameter estimation. Deep neural networks (DNNs) offer a solution to these limitations. Therefore, we aimed to develop simulation-based DNNs for MP-ASL and compared the performance of a supervised DNN (DNNSup), physics-informed unsupervised DNN (DNNUns), and the conventional lookup table method (LUT) using simulation and in vivo data. METHODS: MP-ASL was performed twice during resting state and once during the breath-holding task. First, the accuracy and noise immunity were evaluated in the first resting state. Second, CBF and CBVa values were statistically compared between the first resting state and the breath-holding task using the Wilcoxon signed-rank test and Cliff's delta. Finally, reproducibility of the two resting states was assessed. RESULTS: Simulation and first resting-state analyses demonstrated that DNNSup had higher accuracy, noise immunity, and a six-fold faster computation time than LUT. Furthermore, all methods detected task-induced CBF and CBVa elevations, with the effect size being larger with the DNNSup (CBF, p = 0.055, Δ = 0.286; CBVa, p = 0.008, Δ = 0.964) and DNNUns (CBF, p = 0.039, Δ = 0.286; CBVa, p = 0.008, Δ = 1.000) than that with LUT (CBF, p = 0.109, Δ = 0.214; CBVa, p = 0.008, Δ = 0.929). Moreover, all the methods exhibited comparable and satisfactory reproducibility. CONCLUSION: DNNSup outperforms DNNUns and LUT with respect to estimation performance and computation time.

[Usefulness of Breath-hold DWI Focused on the Hepatic Dome in EOB-MRI].

PURPOSE: Respiratory-triggered-diffusion-weighted imaging (R-DWI) of the liver often results in poor image quality under the diaphragmatic dome on the cephalic side of the liver (hepatic dome) secondary to magnetic field inhomogeneity in liver magnetic resonance imaging (MRI). Hence, the usefulness of additional breath-hold-DWI (B-DWI) focusing on the hepatic dome was investigated. METHODS: A total of 22 patients (14 men and 8 women; mean age 69.0±11.7 years) who underwent ethoxybenzyl (EOB)-MRI at our hospital between July and August, 2022 using a 3.0 T MRI system were included. One radiologist and three radiology technologists visually assessed the visibility of R-DWI and B-DWI in the hepatic dome on a 4-point scale (1 to 4). Additionally, the apparent diffusion coefficient (ADC) values of the hepatic parenchyma on each DWI were compared. RESULTS: B-DWI improved visibility in the hepatic dome compared to R-DWI (2.67±0.71 vs. 3.25±0.43, p<0.05). No significant difference was found in the ADC values for each DWI. CONCLUSION: B-DWI has excellent visibility in the hepatic dome and is expected to complement R-DWI. Therefore, B-DWI is very useful as an additional imaging in EOB-MRI.

Extracellular volume fraction obtained by dual-energy CT depicting the etiological differences of liver fibrosis.

PURPOSE: To assess etiological differences in extracellular volume fraction (ECV) and evaluate its influence on staging performance. METHODS: A total of 166 patients with normal liver (n = 14) and chronic liver disease related to viral hepatitis (n = 71), alcohol (n = 44), and nonalcoholic steatohepatitis (NASH) (n = 37) underwent dual-energy CT (DECT) of the liver (5-min equilibrium-phase images) between January 2020 and July 2022. The iodine densities of the parenchyma and aorta were measured and ECV was calculated. Comparisons of ECV between each etiology and METAVIR fibrosis stage were statistically analyzed (p < 0.05). RESULTS: ECV in each etiology and all patients significantly increased with higher fibrosis stage (p < 0.001) and showed a strong or moderate correlation with fibrosis stage (Spearman's ρ; all patients, 0.701; viral hepatitis, 0.638; alcoholic, 0.885; NASH, 0.791). In stages F2-F4, ECV in alcoholic liver disease was significantly larger than those for viral hepatitis and NASH (p < 0.05); however, no significant difference in stage F1 was found among the three etiologies. The cutoff values and areas under the receiver operating characteristic curve (AUC-ROCs) for discriminating fibrosis stage (≥ F1- ≥ F4) were higher for alcohol (cutoff values and AUC-ROC; 20.1% and 0.708 for ≥ F1, 23.8% and 0.990 for ≥ F2, 24.3% and 0.968 for ≥ F3, and 26.6% and 0.961 for ≥ F4, respectively) compared with those for the others. CONCLUSION: ECV in alcoholic liver disease is higher than that in other etiologies in the advanced stages of fibrosis, and etiological differences in ECV affect the staging performance of fibrosis.

Diagnostic performance of abbreviated gadoxetic acid-enhanced magnetic resonance protocols with contrast-enhanced computed tomography for detection of colorectal liver metastases.

BACKGROUND: Although contrast-enhanced magnetic resonance imaging (MRI) using gadoxetic acid has been shown to have higher accuracy, sensitivity, and specificity for the detection and characterization of hepatic metastases compared with other modalities, the long examination time would limit the broad indication. Several abbreviated enhanced MRI (Ab-MRI) protocols without dynamic phases have been proposed to achieve equivalent diagnostic performance for the detection of colorectal liver metastases. However, an optimal protocol has not been established, and no studies have assessed the diagnostic performance of Ab-MRI combined with contrast-enhanced computed tomography (CE-CT), which is the preoperative imaging of colorectal cancer staging in clinical settings, to determine the best therapeutic strategy. AIM: To compare the diagnostic performance of two kinds of Ab-MRI protocol with the standard MRI protocol and a combination of the Ab-MRI protocol and CE-CT for the detection of colorectal liver metastases. METHODS: Study participants comprised 87 patients (51 males, 36 females; mean age, 67.2 ± 10.8 years) who had undergone gadoxetic acid-enhanced MRI and CE-CT during the initial work-up for colorectal cancer from 2010 to 2021. Each exam was independently reviewed by two readers in three reading sessions: (1) Only single-shot fast spin echo (FSE) T2-weighted or fat-suppressed-FSE-T2-weighted, diffusion-weighted, and hepatobiliary-phase images (Ab-MRI protocol 1 or 2); (2) all acquired MRI sequences (standard protocol); and (3) a combination of an Ab-MRI protocol (1 or 2) and CE-CT. Diagnostic performance was then statistically analyzed. RESULTS: A total of 380 Lesions were analyzed, including 195 metastases (51.4%). Results from the two Ab-MRI protocols were similar. The sensitivity, specificity, and positive and negative predictive values from Ab-MRI were non-inferior to those from standard MRI (P > 0.05), while those from the combination of Ab-MRI protocol and CE-CT tended to be higher than those from Ab-MRI alone, although the difference was not significant (P > 0.05), and were quite similar to those from standard MRI (P > 0.05). CONCLUSION: The diagnostic performances of two Ab-MRI protocols were non-inferior to that of the standard protocol. Combining Ab-MRI with CE-CT provided better diagnostic performance than Ab-MRI alone.

Atlas-based relaxometry and subsegment analysis of the substantia nigra pars compacta using quantitative MRI: a healthy volunteer study.

OBJECTIVE: Parkinson's disease is a neurodegenerative disorder caused by neuronal cell loss in the substantia nigra pars compacta (SNpc). We aimed to perform atlas-based relaxometry using an anatomical SNpc atlas and obtain baseline values of SNpc regions in healthy volunteers. METHODS: Neuromelanin (NM)-sensitive imaging of the midbrain and whole-brain 3D T1 weighted images of 27 healthy volunteers (20 males; aged 36.3 ± 11.5 years) were obtained. An anatomical SNpc atlas was created using NM-sensitive images in standard space, and divided into medial (MG), dorsal (DG), and ventrolateral (VG) groups. Proton density (PD), T1, and T2 values in these regions were obtained using quantitative MRI. The relationships between PD, T1, and T2 values in each SNpc region and age were evaluated. RESULTS: The VG PD value was significantly higher than the MG and DG values. MG, DG, and VG T1 values were significantly different, whereas the T2 value of the MG was significantly lower than the DG and VG values. Moreover, a significant negative correlation between PD and T1 values of the MG and age was observed. CONCLUSION: The PD, T1, and T2 values of the SNpc regions measured in standard space using an anatomical atlas can be used as baseline values. PD and T1 values of the SNpc regions may be associated with NM concentrations. ADVANCES IN KNOWLEDGE: An anatomical SNpc atlas was created using NM-sensitive MRI and can be used for the quantitative evaluation of subsegments of the SNpc in standard space.

Separating spin compartments in arterial spin labeling using delays alternating with nutation for tailored excitation (DANTE) pulse: A validation study using T2 -relaxometry and application to arterial cerebral blood volume imaging.

PURPOSE: To clarify the type of spin compartment in arterial spin labeling (ASL) that is eliminated by delays alternating with nutation for tailored excitation (DANTE) pulse using T2 -relaxometry, and to demonstrate the feasibility of arterial cerebral blood volume (CBVa ) imaging using DANTE-ASL in combination with a simplified two-compartment model. METHOD: The DANTE and T2 -preparation modules were combined into a single ASL sequence. T2 values under the application of DANTE were determined to evaluate changes in T2 , along with the post-labeling delay (PLD) and the relationship between transit time without DANTE (TTnoVS ) and T2 . The reference tissue T2 (T2_ref ) was also obtained. Subsequently, the DANTE module was embedded into the Hadamard-encoded ASL. Cerebral blood flow (CBF) and CBVa were computed using two Hadamard-encoding datasets (with and without DANTE) in a rest and breath-holding (BH) task. RESULTS: While T2 without DANTE (T2_noVS ) decreased as the PLD increased, T2 with DANTE (T2_DANTE ) was equivalent to T2_ref and did not change with the PLD. Although there was a significant positive correlation between TTnoVS and T2_noVS with short PLD, T2_DANTE was not correlated with TTnoVS nor PLD. Baseline CBVa values obtained at rest were 0.64 ± 0.12, 0.64 ± 0.11, and 0.58 ± 0.15 mL/100 g for anterior, middle, and posterior cerebral arteries, respectively. Significant CBF and CBVa elevations were observed in the BH task. CONCLUSION: Microvascular compartment signals were eliminated from the total ASL signals by DANTE. CBVa can be measured using Hadamard-encoded DANTE-ASL in combination with a simplified two-compartment model.