Yasuo Takatsu

The Dixon technique and the frequency-selective fat suppression technique in three-dimensional T1 weighted MRI of the liver: a comparison of contrast-to-noise ratios of hepatocellular carcinomas-to-liver

OBJECTIVE The use of three-dimensional T1 weighted gradient echo sequences such as the Dixon technique and the frequency-selective fat suppression (FS) technique is currently widely accepted method in MRI examinations of the liver. To assess the image qualities of the Dixon technique and the frequency-selective FS technique, the contrast-to-noise ratios (CNRs) of hepatocellular carcinoma (HCC)-to-liver and fat-to-liver were compared between the two techniques in the hepatobiliary phase (HBP) following administration of gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid. METHODS MR images of 59 patients with a total of 86 HCCs were retrospectively evaluated. Images were consecutively obtained with the Dixon and frequency-selective FS methods in the HBP and their CNRs of HCC-to-liver and fat-to-liver were compared. CNRs and contrast ratios were calculated by the mean value of the liver parenchyma, HCC, fat and standard deviation of the liver parenchyma. The Wilcoxon signed-ranks test was used for statistical analysis. RESULTS The median CNRs for the frequency-selective FS and Dixon techniques of HCC-to-liver were 4.3 and 5.4 (p < 0.01), mesenteric fat-to-liver were 9.9 and 12.8 (p < 0.01) and subcutaneous fat-to-liver were 9.9 and 13.2 (p < 0.01), respectively. CONCLUSION The Dixon technique yielded higher CNRs of HCC-to-liver than that of the frequency-selective FS technique. ADVANCES IN KNOWLEDGE There are a limited number of reports on quantitative analysis of the image qualities of the Dixon technique and the frequency-selective FS technique, particularly within the same patient and examination.

Magnetic resonance imaging relaxation times of female reproductive organs

Background Relaxation time of female reproductive organs affects the tissue contrast of magnetic resonance image (MRI), and is used for quantitative analysis. Purpose To evaluate the relaxation times of normal female reproductive organs in the luteal phase of the menstrual cycle. Material and Methods On a 1.5-T MRI, relaxation times were measured in pelvic tissues (endometrium, junctional zone, myometrium, follicle, and stroma) of 32 female healthy volunteers (33.5 ± 6.8 years). The Look–Locker sequence was used to measure T1 relaxation times. Furthermore, a multiple spin-echo method with 32 different echo times was used to measure T2 relaxation times. The images were obtained in the luteal phase of each volunteer’s menstrual cycle. Results The measured relaxation times (means ± standard deviations) were as follows: endometrium (T1, 1703 ± 147 ms; T2, 214 ± 35 ms), junctional zone (T1, 1168 ± 63 ms; T2, 72 ± 12 ms), myometrium (T1, 1314 ± 103 ms; T2, 138 ± 20 ms), follicle (T1, 2267 ± 249 ms; T2, 603 ± 68 ms), and stroma (T1, 1481 ± 129 ms; T2, 126 ± 29 ms). Conclusion Reliable MRI measurements of T1 and T2 relaxation times of normal female reproductive organs in the luteal phase of the menstrual cycle are useful as references to recognize the normal value.

A novel method for evaluating enhancement using gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid in the hepatobiliary phase of magnetic resonance imaging.

To investigate whether quantitative liver-portal vein contrast ratio (Q-LPC) can be used as a substitute for quantitative liver-spleen contrast ratio (Q-LSC) in the hepatobiliary phase (HBP) contrasting degree. Q-LSC and Q-LPC were calculated in HBP images that were obtained approximately 20 min after gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid injection, and relationship between them was evaluated. A very strong correlation was observed between Q-LSC and Q-LPC with respect to Child-Pugh class. Furthermore, Q-LPC values were not significantly different between patients with splenectomy or Gamna-Gandy bodies and those without. Therefore, Q-LPC can be useful instead of Q-LSC in patients with splenectomy or Gamna-Gandy bodies.

Hepatobiliary phase images using gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid-enhanced MRI as an imaging surrogate for the albumin-bilirubin grading system.

OBJECTIVES To clarify the correlation between hepatobiliary phase (HBP) images using gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid (Gd-EOB-DTPA) and albumin-bilirubin (ALBI) grading system. MATERIALS AND METHODS We evaluated 220 consecutive patients who underwent liver magnetic resonance imaging with Gd-EOB-DTPA. Quantitative liver-spleen contrast ratio (Q-LSC) was calculated in HBP images approximately 20min after Gd-EOB-DTPA administration. To evaluate the degree of association between Q-LSC and ALBI grade, the Child-Pugh (C-P) score was used for comparison. Correlation coefficients were calculated, and median Q-LSC values were compared with the C-P scores and ALBI grades. The Steel-Dwass multiple comparison test was used for statistical analysis. RESULTS The correlation coefficient between Q-LSC and C-P score was -0.35, P<0.0001, and the ALBI grade was -0.61, P<0.0001. Q-LSC of overall median, C-P A, B, and C were 1.94, 1.91, 1.96, and 1.33, respectively. The differences between C-P A and C-P B, C-P B and C-P C, and C-P A and C-P C were P=0.999, 0.126, and 0.149, respectively. Q-LSC of the overall median, ALBI grade 1, 2, and 3 were 1.94, 2.12, 1.69, and 1.30, respectively. The differences between ALBI grades 1 and 2, 2 and 3, and 1 and 3 were P<0.0001, P=0.0466, and P=0.0035, respectively. Q-LSC was better correlated and discriminated by ALBI grade than C-P score. CONCLUSION A strong correlation was observed between Q-LSC of an HBP image with Gd-EOB-DTPA and ALBI grade; HBP imaging could be a surrogate for the ALBI grade.

Radiofrequency-shielding Effect of a Titanium Mesh Implanted for Cranioplasty

PURPOSE After cranioplasty with a titanium mesh, radiofrequency (RF)-shielding images appear during magnetic resonance (MR) imaging. To clarify their influence, we evaluated the effect of mesh position, phase-encoding direction, and type of coil employed. MATERIALS AND METHODS On a 1.5-tesla MR imager, we placed a titanium mesh board (100 × 100 × 0.8 mm) on the surface of a cubic phantom to mimic a human brain and used a quadrature coil and an 8-channel neurovascular coil to measure nonuniformity, signal decay ratio, and the B1 map. RESULTS Nonuniformity was 6.7 times higher at the quadrature head coil and 1.6 times higher at the neurovascular coil when the mesh was on the phantoms right side or anterior to it than when it was on its superior end or absent. The profile of the signal decay ratio increased by 1.9% mm(-1) from 0 to 40 mm from the mesh side to the base value at the quadrature head coil when the mesh was on the phantoms right side and 0.9% mm(-1) from 0 to 80 mm at the neurovascular coil when the mesh was on the phantoms right side or anterior to it. The quadrature head coil showed greater incline of the profile when the mesh was on the right in coronal and axial views and no notable change in the profile in coronal and sagittal views when the mesh was on the superior end. In the B1 map, the flip angle was lower when the mesh was nearer. CONCLUSION The response to the RF-shielding effect from a titanium mesh depends on the location of the mesh and the RF coil used but not on the phase-encoding direction.

Influence of arm position and respiration technique during liver examinations on the detectability of mammary lesions

During liver computed tomography (CT), scanning is performed with the raised arm position and an inhalation technique. However, for liver magnetic resonance imaging (MRI), the arms are placed at the sides of the body and an exhalation technique is used. This study was aimed at evaluating the effect that the patient’s arm position and respiration technique had on the ability to detect mammary glands in the scan range to discover unexpected mammary lesions during the liver MRI examination. Liver MRI and CT images were compared for 337 female patients. More than half of the mammary glands were included in 97.3% of MRI, but in 4.7% of CT. No mammary lesions were found during CT, whereas seven were found during MRI. The mammary lesions are more likely to be detected when the patient places her arms at the sides of the body and uses the exhalation technique during liver MRI.

Assessment of the Quality of Breast MR Imaging Using the Modified Dixon Method and Frequency-Selective Fat Suppression: A Phantom Study

To obtain objective and concrete data by physically assessing the quality of breast magnetic resonance images based on the fat-suppression effect by the modified Dixon method (mDixon) and frequency-selective fat suppression (e-Thrive) using an original lipid-content breast phantom that could easily reveal the influence of non-uniform fat suppression in breast magnetic resonance imaging. The fat-suppression uniformity was approximately seven times superior when using mDixon compared with when using e-Thrive. mDixon appears to have a significant advantage.

Brain magnetic resonance imaging using a customized vacuum shape-keeping immobilizer without sedation in preterm infants

OBJECTIVE To validate that a customized vacuum shape-keeping immobilizer (VaSKI) can be used in preterm infants without sedation. METHODS Preterm infants who underwent brain MRI from February 2008 to March 2017 at Osaka Medical College Hospital were retrospectively assigned to the sedation group (February 2008 to September 2013, n = 64) or VaSKI group (October 2013 to November 2016, n = 64). The examination success rates and diagnosable case classification were determined by pediatricians and radiologists. We compared the time from preparation to examination completion between the groups. Furthermore, we measured the time from immobilization to sleep in the preterm infants in the VaSKI group. RESULTS The examination success rate was 90.6% in both of the groups. The median (interquartile range) times of preparation were 24.0 (15.3) and 18.0 (13.0) min in the sedation and VaSKI groups, respectively. In the VaSKI group, the time from immobilization to sleep was within 3 min in 87.1% of the preterm infants. CONCLUSIONS The brain MRI examination success rates and motion artifact suppression effects were equivalent between the groups, whereas the time from preparation to examination completion was much shorter in the VaSKI group. Therefore, the VaSKI was validated as an immobilizer for MRI in preterm infants without using sedation.

Visual criterion for evaluating hepatobiliary phase image acquisition of gadolinium-ethoxybenzyl-diethylenetriaminepentaacetic acid-enhanced MRI

AIM To evaluate the hepatobiliary phase (HBP) of liver magnetic resonance imaging (MRI) using gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid, and report a visual criterion based on the portal vein (PV), which can be used as a substitute for the quantitative liver-spleen contrast ratio (Q-LSC). MATERIALS AND METHODS In HBP images of 167 patients, a visual criterion was established based on the sufficient contrast between the liver parenchyma (LP) and PV. The Q-LSC was calculated for patients to assess whether the cut-off value of 1.5 was exceeded. The correlation between the signal intensities in the PV and tumours were determined and comparisons were made. The contrast between LP and the tumour was visually assessed with scores ranging from 1 to 3 defined as poor, fair, and good, respectively. The correlation between Q-LSC and quantitative liver-PV contrast ratio (Q-LPC) was also assessed. RESULTS The Q-LSC was <1.5 in all patients who did not meet the visual criterion. There was a strong correlation between the signal intensities in the PV and tumours (r=0.72), and no significant differences (p=0.99) were found between the signal intensities in PV and tumours by Wilcoxons signed-rank test. Significant differences of all the combinations were found using Steel-Dwass multiple comparisons in the visual assessments of contrasts between LP and tumour. The correlation between Q-LSC and Q-LPC was strong (r=0.82). CONCLUSIONS The visual criterion based on the PV was suitable for the assessment of HBP images as a substitute for Q-LSC.

Diffusion kurtosis imaging in the assessment of liver function: Its potential as an effective predictor of liver function

OBJECTIVES: We aimed to determine whether diffusion kurtosis imaging (DKI) analysis with the breath-hold technique can replace liver function results obtained from laboratory tests. METHODS: Patients (n = 79) suspected of having a hepatobiliary disease, and control group without liver diseases (n = 15) were examined with non-Gaussian diffusion-weighted imaging using a 3.0 T magnetic resonance imaging unit. Based on the findings of DKI, various blood serum parameters, including the indocyanine green (ICG) retention rate 15 min after an intravenous injection of ICG (ICG-R15) and mean kurtosis values and Child-Pugh and albumin-bilirubin (ALBI) scores, were calculated. In total, 17 patients were tested using ICG-R15. For evaluating liver function, correlations between the mean kurtosis value and the Child-Pugh score, ALBI score, and ICG-R15 value as indicators of liver function obtained from blood data were assessed using Spearmans rank correlation. In apparent diffusion coefficient as well, we assessed correlations with these indicators. RESULTS: The mean kurtosis value correlated with the Child-Pugh score (Spearmans rank-correlation coefficient, ρ = 0.3992; p < 0.0001). Moreover, the mean kurtosis value revealed a correlation with the ICG-R15 value (Spearmans rank-correlation coefficient, ρ = 0.5972; p = 0.00114). The correlation between the mean kurtosis value and the ALBI score was the poorest among these (Spearmans rank-correlation coefficient, ρ = 0.3395; p = 0.0008). CONCLUSION: Liver function correlating with the Child-Pugh score and ICG-R15 value can be quantitatively estimated using the mean kurtosis value obtained from DKI analysis. DKI analysis with the breath-hold technique can be used to determine liver function instead of performing laboratory tests. ADVANCES IN KNOWLEDGE: Previous studies have not evaluated liver function in vivo using DKI.