Masatoshi Tsunoda

Development of a tissue-equivalent MRI phantom using carrageenan gel.

A new tissue‐equivalent MRI phantom based on carrageenan gel was developed. Carrageenan gel is an ideal solidifying agent for making large, strong phantoms in a wide variety of shapes. GdCl3 was added as a T1 modifier and agarose as a T2 modifier. The relaxation times of a very large number of samples were estimated using 1.5‐T clinical MRI equipment. The developed phantom was found to have a T1 value of 202–1904 ms and a T2 value of 38–423 ms when the GdCl3 concentration was varied from 0–140 μmol/kg and the agarose concentration was varied from 0–1.6% in a carrageenan concentration that was fixed at 3%. The range of measured relaxation times covered those of all types of human tissue. Empirical formulas linking the relaxation time with the concentration of the modifier were established to enable the accurate and easy calculation of the modifier concentration needed to achieve the required relaxation times. This enables the creation of a phantom having an arbitrary combination of T1 and T2 values and which is capable of retaining its shape. Magn Reson Med 50:1011–1017, 2003.

Sclerosing stromal tumor of the ovary: US, MR, and dynamic MR findings

The US, MR, and dynamic MR findings in four patients with sclerosing stromal tumor of the ovary are reported. US showed a tumor with multilocular cystic components and irregularly thickened septa and tumor walls or a solid tumor including several small cystic components. On T2-weighted MR images, signal intensities of the cystic components were high and those of the solid components were inhomogeneous, ranging from intermediate-high to high. Dynamic MRI demonstrated marked early enhancement of the solid components.

Hepatectomy simulation discrepancy between radionuclide receptor imaging and CT volumetry: influence of decreased unilateral portal venous flow.

Background: Regional dysfunction demonstrated by Tc-99m-diethylenetriamine-penta-acetic acid-galactosyl human serum albumin (GSA) scintigraphy due to regional decrease in the portal venous flow has previously been reported. In this study, we call attention to the significance of unilateral portal venous flow decrease for preoperative hepatectomy simulation, and evaluate the hepatectomy simulation discrepancy between Tc-99m-GSA single-photon emission computed tomography (SPECT) and CT volumetry.Methods: Twenty-four hepatectomy candidates underwent preoperative hepatectomy simulation by both Tc-99m-GSA SPECT and CT volumetry. Both anatomical and functional resection ratios were calculated by means of CT volumetry and Tc-99m-GSA SPECT, respectively. The differences and ratios between anatomical and functional resection ratios were calculated in all patients, and compared in patients with and without unilateral portal venous flow decrease.Results: Anatomical resection ratios were 28.0±11.7 (mean±standard deviation) in patients with unilateral portal venous flow decrease, and 42.1±15.7 in patients without unilateral portal venous flow decrease (p=0.0127). Functional resection ratios were 14.7±12.8 in patients with unilateral portal venous flow decrease and 40.5±14.6 in patients without (p=0.0004). The differences between anatomical and functional resection ratios were 13.0±7.9 in patients with unilateral portal venous flow decrease and 5.6±3.1 in patients without (p=0.0009). The ratios between anatomical and functional resection ratios were 0.48±0.29 in patients with unilateral portal venous flow decrease and 0.86±0.10 in patients without (p=0.0018). In 12 of the 13 patients with unilateral portal venous flow decrease, anatomical resection ratios were found to be larger than functional resection ratios, whereas this happened in only 6 of 11 patients without unilateral portal venous flow decrease (p=0.0063).Conclusion: Unilateral portal venous flow decrease is suspected to be a major factor in the discreapancy between hepatectomy simulations with radionuclide receptor imaging and CT volumetry.

Bile duct stenosis due to portal cavernomas: MR portography and MR cholangiopancreatography demonstration.

We report two cases of bile duct stenosis due to portal cavernomas. Smooth stenoses were seen arising from both walls of the common bile duct on magnetic resonance (MR) cholangiopancreatography. On contrast-enhanced MR portography, peribiliary tortuous vessels were evident, indicating portal cavernomas. MR imaging can evaluate the biliary tree and portal systems noninvasively and was useful for evaluating this condition.

Portal blood flow in the presence or absence of diffuse liver disease: measurement by phase contrast MR imaging

Background:In patients with diffuse liver disease, the portal flow dynamics change markedly in accordance with disease progression and would provide a useful index of progression of stage.Methods:Portal blood flow (PBF) was measured by phase contrast magnetic resonance imaging (MRI) in 21 patients with diffuse liver disease and 20 healthy volunteers. The MRI method was validated by a flow phantom study. The mean PBF could be measured in 6.8 min without breath-holding.Results:Doppler ultrasound measurements of PBF volume were obtained reproducibly in all the healthy volunteers and were shown to correlate with the MRI values (Doppler: 12.5 ±3.2 cm3/s, MRI: 12.0 ± 3.3 cm3/s; mean ± SD). The PBF volume of patients with chronic hepatitis showed no significant difference from that of the healthy volunteers. In patients with liver cirrhosis, the PBF volume ranged from 5.01 to 32.3 cm3/s. A significant increase in PBF volume was caused in one patient by massive intrahepatic shunting and a significant decrease was caused in two patients by massive extrahepatic shunting.Conclusions:The measurement of PBF by phase contrast MRI is clinically useful in predicting intrahepatic or extrahepatic shunting in patients with liver cirrhosis, and may be of value in detecting the progression of stage in diffuse liver diseases.

Development of a phantom compatible for MRI and hyperthermia using carrageenan gel—relationship between T1 and T2 values and NaCl concentration

The authors developed a phantom, designated as the CAGN phantom, compatible for MRI and hyperthermia that is useful in the fundamental studies of non-invasive MR thermometry. The ingredients of this phantom are carrageenan, GdCl3 as a T1 modifier, agarose as a T2 modifier, NaCl as a conductivity modifier, NaN3 as an antiseptic and distilled water. Another phantom that was developed, the CAG phantom, has relaxation times that are adjustable to those of any human tissue. To use this phantom for electromagnetic heating, NaCl was added to change the conductivity of the phantom and clarified the relationship between the conductivity and NaCl concentration. This study examined the relationship between relaxation times and NaCl concentration of the CAGN phantom. The results showed that both T1 and T2 values were affected by NaCl and the experimental results led to the empirical formulae expressing the relationship between the relaxation rates (1/T1, 1/T2) and the concentrations of GdCl3, agarose and NaCl. The appropriate concentrations of T1 and T2 modifiers were calculated from these empirical formulae when making a specified phantom that has the required relaxation times and NaCl concentration.

Development of a phantom compatible for MRI and hyperthermia using carrageenan gel--relationship between dielectric properties and NaCl concentration.

A phantom has previously been developed containing carrageenan, agarose and gadolinium chloride (called CAG phantom) for MRI with 1.5 T. T1 and T2 relaxation times of this phantom are independently changeable by varying concentrations of relaxation-time modifiers to simulate relaxation times of the various types of human tissues. The CAG phantom has a T1 value of 202–1904 ms and a T2 value of 38–423 ms, when the GdCl3 concentration is varied from 0–140 µmol/kg and the agarose concentration is varied from 0–1.6%. A new phantom has now been developed (called CAGN phantom), made by adding an electric conductive agent, NaCl, to the CAG phantom for use in the areas of MRI and hyperthermia research. Dielectric properties of the CAGN phantom were measured and the results of experiments were expressed by the Cole–Cole equation in the frequency range of 5–130 MHz. The relationship between the conductivity of the CAGN phantom and the concentration of NaCl was expressed by a linear function in the frequency range of 1–130 MHz. The linear function involves a parameter of frequency and, when the frequency is 10 MHz, the conductivity of the CAGN phantom can be changed from 0.27–1.26 Sm−1 by increasing the NaCl concentration from 0–0.7%. The CAGN phantom developed can be employed in basic experiments for non-invasive temperature measurement using MRI and as a loading phantom for MRI with up to 3 T.

Nontumorous decrease in Tc-99m GSA accumulation

Nontumorous decrease in99mTc-GSA accumulation has not been well covered in the literature. Understanding of this phenomenon is, however, essential for accurate evaluation of regional hepatic function. Scintigrams (transaxial SPECT) of 269 patients who underwent99mTc-GSA liver scintigraphy were reviewed for the presence of nontumorous decreases in99mTc-GSA accumulation. Nontumorous decreases in99mTc-GSA accumulation were seen in 32 of 269 patients (12%). In 16 of the 32 patients (6%), nontumorous decreases in99mTc-GSA accumulation corresponded to regional decrease in portal venous flow. The causes of such decrease in portal venous flow were portal thrombus of hepatocellular carcinomas in eight patients, portal venous stenosis or occlusion by hilar cholangiocarcinomas in five patients, inter alia. In eight patients (3%), the regions with decreased99mTc-GSA accumulation correlated with massive hepatic necrosis in fulminant hepatitis, scar in hepatitis, or confluent fibrosis in cirrhotic liver. In two patients (0.7%) with hilar cholangiocarcinomas, the possible causes of lobar decrease in99mTc-GSA accumulation were thought to be lobar decrease in portal venous flow, lobar biliary stasis, or both. In four patients (1.5%), the exact causes of nontumorous decrease in99mTc-GSA accumulation could not be determined.