Junji Takahashi

Diffusion analysis with triexponential function in liver cirrhosis

To acquire more detailed information noninvasively through on diffusion and perfusion in normal and cirrhotic livers, we analyzed three diffusion components using triexponential function.

Influence of Gadoxetate Disodium on Oxygen Saturation and Heart Rate during Dynamic Contrast-enhanced MR Imaging.

PURPOSEnTo investigate whether gadoxetate disodium affects peripheral capillary oxygen saturation (SpO2) and/or heart rate (HR) during dynamic contrast material-enhanced (DCE) magnetic resonance (MR) imaging in patients with liver diseases.nnnMATERIALS AND METHODSnThis retrospective study was approved by the institutional review board, who waived the requirement for informed consent. Four hundred fifty-eight patients (171 women [mean age, 66.5 years; range, 23-87 years] and 287 men [mean age, 61.1 years; range, 25-89 years]) who underwent liver DCE MR imaging with gadoxetate disodium (0.025 mmol per kilogram of body weight) from October 28, 2013, to June 24, 2014, were included in this study. They were monitored for SpO2 and HR during DCE MR imaging. Motion artifact severity was graded by using a five-point scale, and transient severe motion (TSM) was defined by a score of at least 4. The association between TSM and baseline predictors was assessed, and HR and SpO2 at each postcontrast phase were compared with those at the precontrast phase in the TSM and non-TSM groups.nnnRESULTSnFour hundred thirty-six patients were included in the non-TSM group, and 22 were included in the TSM group. Although the motion score was the worst at the arterial phase, the observed mean differences in SpO2 and HR between the precontrast phase and the arterial phase were less than 1% and 5 beats per minute, respectively (mean SpO2 ± standard deviation for the non-TSM group, 96.7% ± 1.8 vs 96.9% ± 1.8 [P = .11]; SpO2 for the TSM group, 96.4% ± 1.6 vs 96.1% ± 1.6 [P > .99]) (HR for the non-TSM group, 68.9 beats per minute ± 12.4 vs 70.9 beats per minute ± 12.1 [P < .0001]; HR for the TSM group, 75.0 beats per minute ± 11.8 vs 79.9 beats per minute ± 10.2 [P < .0001]).nnnCONCLUSIONnIntravenous gadoxetate disodium (a weight-based dose) does not cause changes in SpO2 and HR that lead to image quality degradation.

Hepatic fat quantification using the two-point Dixon method and fat color maps based on non-alcoholic fatty liver disease activity score.

The two‐point Dixon method for magnetic resonance imaging (MRI) is commonly used to non‐invasively measure fat deposition in the liver. The aim of the present study was to assess the usefulness of MRI‐fat fraction (MRI‐FF) using the two‐point Dixon method based on the non‐alcoholic fatty liver disease activity score.

Diffusion analysis with triexponential function in hepatic steatosis

Our purpose was to assess the influence of liver steatosis on diffusion by triexponential analysis. Thirty-three patients underwent diffusion-weighted magnetic resonance imaging with multiple b values for perfusion-related diffusion, fast free diffusion, and slow restricted diffusion coefficients (Dp, Df, Ds) and fractions (Fp, Ff, Fs). They also underwent dual-echo gradient-echo imaging for measurement of the hepatic fat fraction (HFF). Of these, 13 patients were included in the control group and 20 in the fatty liver group with HFF >5xa0%. The parameters of the two groups were compared by use of the Mann–Whitney U test. The relationships between diffusion coefficients and HFFs were assessed by use of the Pearson correlation. Dp and Df were reduced significantly in the steatotic liver group compared with those in the control group (Dpxa0=xa027.72xa0±xa06.61xa0×xa010−3 vs. 33.33xa0±xa06.47xa0×xa010−3xa0mm2/s, Pxa0=xa00.0072; Dfxa0=xa01.70xa0±xa00.53xa0×xa010−3 vs. 2.06xa0±xa00.40xa0×xa010−3xa0mm2/s, Pxa0=xa00.0224). There were no significant differences in the other parameters between the two groups. Furthermore, Dp and Df were correlated with HFF (Pxa0<xa00.0001, rxa0=xa0−0.64 and Pxa0=xa00.0008, rxa0=xa0−0.56, respectively). Decreased liver perfusion in steatosis caused the reduction in Dp, and extracellular fat accumulation and intracellular fat droplets in steatosis led to the reduction in Df. Thus, the influence of hepatic steatosis should be taken into consideration when triexponential function analysis is used for assessment of diffuse liver disease.

Evaluation of six-point modified dixon and magnetic resonance spectroscopy for fat quantification: a fat–water–iron phantom study

This study aimed to evaluate (1) the agreement between the true fat fraction (FF) and proton density FF (PDFF) measured using a six-echo modified Dixon (6mDixon) and magnetic resonance spectroscopy (MRS) and (2) the influence of fat on T2* values. The study was performed using phantoms of varying fat and iron content. Point-resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM) with single-echo (S) and multiecho (M) (PRESS-S, PRESS-M, STEAM-S, and STEAM-M) were used for MRS. In phantoms without iron, the agreement between the true FF and measured PDFF was tested using Bland–Altman analysis. The influence of iron on PDFF was evaluated in phantoms with iron. The relationship between the true FF and T2* value was assessed in phantoms without iron, wherein the mean differences (limits of agreement) for each method were as follows: 6mDixon 2.9% (−2.4 to 8.1%); STEAM-S 3.2% (−9.5 to 16.0%); STEAM-M −0.7% (−6.9 to 5.5%); PRESS-S 8.9% (−14.5 to 32.4%); and PRESS-M −5.8% (−18.3 to 6.7%). In the 20% fat phantoms with iron, as iron increased, PDFFs with STEAM-S, PRESS-S, and PRESS-M were considerably overestimated, while, PDFF with STEAM-M was stable at 0.04–0.2xa0mM iron concentrations (17.2 and 21.4%, respectively), and PDFF with 6mDixon was reliable at even 0.4xa0mM iron concentration (24.8%). The T2* value showed a negative correlation with the true FF (rxa0=xa0−0.942, Pxa0=xa00.005). STEAM-M and 6mDixon were reliable methods of fat quantification in the absence of iron, and the T2* value was shortened by fat.

Three-dimensional magnetic resonance imaging for stringent diagnosis of advanced fibrosis associated with nonalcoholic steatohepatitis.

BackgroundThe definitive diagnosis of nonalcoholic steatohepatitis (NASH) is currently based on histopathological assessment. This study aimed to elucidate the utility of a novel noninvasive method, three-dimensional magnetic resonance imaging (3D-MRI), for diagnosing advanced fibrosis in patients with NASH, using histopathological diagnosis as the reference standard.MethodsThis retrospective study included 30 consecutive patients who had been diagnosed with NASH by histopathology and had undergone 3D-MRI before biopsy. 3D-MRI provided a three-dimensional reconstruction of the liver from contrast-enhanced hepatobiliary phase MR images. In the present study, histopathological advanced fibrosis was defined as stage 3 and 4 NASH. Advanced fibrosis, diagnosed by 3D-MRI, was considered to be diffuse irregularity of the entire surface of the liver. The diagnostic features of 3D-MRI and the noninvasive evaluation systems (APRI, FIB-4 index, and BARD score) for identifying advanced and nonadvanced fibrosis of NASH were determined and compared.ResultsNine (30xa0%) of the 30 study patients were diagnosed histopathologically with advanced fibrosis, and 11 (37xa0%) of 30 patients were diagnosed with advanced fibrosis using 3D-MRI. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 3D-MRI for diagnosing advanced fibrosis were 100, 90, 82, and 100xa0%, respectively. The sensitivities of APRI, the FIB-4 index, and BARD score ranged from 78 to 89xa0%, the specificities from 71 to 90xa0%, the PPVs from 54 to 78xa0%, and the NPVs from 88 to 94xa0%.ConclusionCompared with the common noninvasive methods for diagnosing advanced fibrosis associated with NASH, 3D-MRI was more accurate.

Noninvasive Assessment of Advanced Fibrosis Based on Hepatic Volume in Patients with Nonalcoholic Fatty Liver Disease

Background/Aims Noninvasive liver fibrosis evaluation was performed in patients with nonalcoholic fatty liver disease (NAFLD). We used a quantitative method based on the hepatic volume acquired from gadoxetate disodium-enhanced (Gd-EOB-DTPA-enhanced) magnetic resonance imaging (MRI) for diagnosing advanced fibrosis in patients with NAFLD. Methods A total of 130 patients who were diagnosed with NAFLD and underwent Gd-EOB-DTPA-enhanced MRI were retrospectively included. Histological data were available for 118 patients. Hepatic volumetric parameters, including the left hepatic lobe to right hepatic lobe volume ratio (L/R ratio), were measured. The usefulness of the L/R ratio for diagnosing fibrosis ≥F3–4 and F4 was assessed using the area under the receiver operating characteristic (AUROC) curve. Multiple regression analysis was performed to identify variables (age, body mass index, serum fibrosis markers, and histological features) that were associated with the L/R ratio. Results The L/R ratio demonstrated good performance in differentiating advanced fibrosis (AUROC, 0.80; 95% confidence interval, 0.72 to 0.88) from cirrhosis (AUROC, 0.87; 95% confidence interval, 0.75 to 0.99). Multiple regression analysis showed that only fibrosis was significantly associated with the L/R ratio (coefficient, 0.121; p<0.0001). Conclusions The L/R ratio, which is not influenced by pathological parameters other than fibrosis, is useful for diagnosing cirrhosis in patients with NAFLD.

Influence of the reference scan and scan time on the arterial phase of liver magnetic resonance imaging

The controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) technique can decrease scan time. The purpose of this study was to determine whether an arterial phase scan can be performed in 5xa0s using the CAIPIRINHA short-scan and a reference scanning technique. The generalized autocalibrating partially parallel acquisition (GRAPPA), the CAIPIRINHA routine (CAIPI-routine), and the CAIPIRINHA short-scanning (CAIPI-short) methods were compared. The scan time for each method was preset to 20xa0s, 15xa0s, and 10xa0s, respectively. The reference scan had a scan time of 5xa0s. A phantom study was used to compare the influence of artifacts during the reference scan. For comparison, the phantom was moved during the last 5xa0s. In the clinical studies of suspected chronic liver diseases, magnetic resonance imaging of the liver is usually performed while the patient is breath-hold. The motion artifacts of each method were compared. Artifacts were reduced in reference scans using the CAIPIRINHA method. At 5xa0s after initiation, the rate of change in the standard deviation value was within 30% compared to that of the original image. Motion artifacts due to the influence of the reference scan when a patient failed to hold their breath did not complicate image evaluation. The proportion of motion artifacts for each sequence was as follows: GRAPPA, 5.8%; CAIPI-routine, 1.9%; and CAIPI-short, 0.7%. The arterial phase can be scanned in 5xa0s using the CAIPI-short and reference scan techniques.

Vascular screening in asymptomatic subjects using non-contrast MRA

Summary Vascular screening including the coronary, carotid, renal arteries and aorta using non-contrast MRA in 300 asymptomatic subjects detected atherosclerosis lesions including the coronary artery in 5% of participants. Background Atherosclerosis is a systemic disease affecting arteries in a whole body and a major cause of death in the world. There are few data, however, on the extent of the diseases associated with atherosclerosis in asymptomatic subjects.