Teiyu Yamauchi

Transient hepatic attenuation differences on dynamic computed tomography.

Transient hepatic attenuation differences (THAD) are occasionally noted on dynamic CT in patients with portal vein obstruction, arterioportal shunt, liver tumor, and liver abscess. We report four additional cases of THAD with unreported and/or unexplained etiology.

Retrievable IVC Filter: Preliminary in Vitro and in Vivo Evaluation

PURPOSE To develop an inferior vena cava (IVC) filter that is retrievable even after neointimal formation and incorporation into the caval wall. MATERIALS AND METHODS Eight filters were placed percutaneously in the infrarenal IVC of eight dogs. Four weeks after placement, percutaneous retrieval of the filters was attempted. Vena cavograms were obtained before and immediately after retrieval. Three dogs were killed immediately after the retrieval procedure was completed. In the other five dogs, follow-up vena cavography was performed 4-14 weeks after retrieval, and autopsy was performed. RESULTS The filters were placed and retrieved successfully in all eight dogs. No migration, caval penetration, or tilting occurred. The IVCs were completely patent both before and immediately after retrieval in all eight dogs. In the three dogs killed immediately after retrieval, neointimal hyperplasia was seen around the struts, but there was no detachment. Delayed stenosis was not seen in any of the five dogs that were followed up, and the inner surface of the caval wall was smooth. CONCLUSION This IVC filter can be easily placed and safely retrieved percutaneously, even after neointimal formation.

Accuracy of attenuation measurement of vascular wall in vitro on computed tomography angiography: Effect of wall thickness, density of contrast medium, and measurement point.

Objectives:We sought to assess the effects of measurement point, wall thickness, and intravascular density of contrast material on attenuation measurement of vascular wall. Materials and Methods:We used vascular models (actual attenuation value of the wall: 83 HU) with wall thicknesses of 1.5, 1.0, or 0.5 mm, filled with contrast material of 254, 325, or 400 HU. The 9 vascular models were fixed in an oil-filled container and scanned with a 16-detector computed tomography. The wall attenuation values were measured at 1 point for 0.5-mm thickness models, 3 for 1.0-mm thickness models, and 5 for 1.5-mm thickness models with the same interval of 0.25 mm. Total 20 measurements were done for each point. Results:For 1.0-mm and 1.5-mm thickness models, wall attenuation progressively increased as the measurement points approached the lumen (P < 0.0001). At all the measurement points for 0.5-mm and 1.0-mm thickness models and the 2 inner measurement points for 1.5-mm thickness models, the densities of contrast material affected the wall attenuations significantly (P < 0.0001). At the midportion for 1.5-mm thickness models, the wall attenuations were not affected by the densities of the contrast material (P = 0.6301), and were 65–68 HU. Conclusions:The effects of the intravascular density of contrast material, measurement point, and wall thickness should be considered in the attenuation measurement of the wall.

Effect of superparamagnetic iron oxide-enhanced MRI of the liver with hepatocellular carcinoma and hyperplastic nodule.

Purpose To evaluate the possibility of superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance imaging (MRI) of the liver in predicting the histologic grade of hepatocellular carcinoma (HCC) and differentiating HCC from benign hyperplastic nodule (HPN). Materials and Methods Thirty patients with 31 histologically proved HCC and HPN underwent MRI (1.5 Tesla). HCCs were graded into well-differentiated HCC (HCCw; n = 10) and moderately to poorly differentiated HCC (HCCmp; n = 15). HPN was categorized into dysplastic nodule (DN; n = 1) and focal nodular hyperplasia (FNH; n = 6). T2-weighted fast spin echo images were obtained before and after administration of SPIO. Signal-to-noise ratios (SNR) of the lesion and surrounding liver parenchyma and contrast-to-noise ratios (CNR) were calculated pre- and postcontrast study. Relative enhancement ratios (RER), also known as signal intensity reduction ratios of the lesions, were also calculated. Results HCCw, HCCmp, DN, and FNH decreased in SNR after injection of SPIO. RER of HCCw was 19.5 ± 13.3%, that of HCCmp was 6.8 ± 5.8%, DN was 44.0%, and FNH was 42.9 ± 4.8%. Significant statistical differences were seen between HCCw and HCCmp and HCC and HPN in RER. HCCw, HCCmp, and DN increased in CNR, and FNH decreased in CNR, but no lesion showed a statistically significant difference in CNR. Conclusion SPIO-enhanced MR images may help to predict the histologic grade of HCC and distinguish HCC from HPN.

CT demonstration of fluid-fluid levels in nonenhancing hemangiomas of the liver.

A fluid-fluid level was observed in three cases of liver hemangioma and in two cases of liver cancer. The patients with hemangioma of the liver did not show enhancement on dynamic CT and the fluid-fluid levels were not detected by ultrasound in two of these patients. Fluid-fluid levels detected by CT but not by ultrasound strongly suggested the diagnosis of nonenhancing hemangioma of the liver.

Optimum iodine concentration of contrast material through microcatheters: hydrodynamic analysis of experimental results.

It is important to increase the iodine delivery rate (I), that is the iodine concentration of the contrast material (C) x the flow rate of the contrast material (Q), through a catheter to obtain high quality arteriograms. The iodine delivery rate varies depending on the iodine concentration of the contrast material. The purpose of this study is to estimate the optimum iodine concentration (Copt) of contrast material (i.e. the iodine concentration at which I becomes maximum) through a microcatheter of a given length (L), inner diameter (D) and injection pressure (P). Iohexol, ioversol and iopamidol of 11-12 iodine concentrations (140-350, 160-350 or 160-370 mg cm(-3)) at 37 degrees C are used. I and Reynolds number (Re) of the flow of each contrast material through four microcatheters (0.49-0.68 mm in inner diameter, 1000-1500 mm in length) at injection pressures of 1.38, 2.76, 4.14 and 5.52 x 10(6) Pa (200, 400, 600 and 800 pounds per square inch) are obtained experimentally. The relationships between I and C and between I and Re are examined for each catheter and injection pressure. Copt is 160-280 mg cm(-3) for iohexol, 180-280 mg cm(-3) for ioversol and 200-300 mg cm(-3) for iopamidol. I becomes maximum when Re approximates the critical Reynolds number (Re approximately 2300). Utilizing this principle, we can estimate Copt and its flow rate through a microcatheter of a given L, D and P.

A one-stage method for obtaining CT during arterial portography and hepatic arteriography.

We describe a new technique for performing CT during arterial portography (CTAP) and during hepatic arteriography (CTHA) in a one-stage procedure, using a coaxial balloon catheter system and slip-ring CT equipment. This technique was employed in 10 patients with liver neoplasms. Both CTAP and CTHA images were obtained in all patients.

Assessment of coronary stent in vitro on multislice computed tomography angiography: improved in-stent visibility by the use of 140-kV tube voltage.

Objective: To assess the effect of tube voltage on the in-stent visibility of coronary stents in vitro on computed tomography (CT) angiography. Methods: A total of 6 vascular models (3 models without stenosis and 3 with stenosis) using 3 kinds of stent (Bx Velocity, Express2, and Driver) with an inner diameter of approximately 3.5 mm and filled with contrast material (CT attenuation, 450 Hounsfield units) were scanned by means of a 16-detector row CT. We assessed the visual stenosis evaluation and inhomogeneity of stent lumen in 4 orientations (0-, 30-, 60-, and 90-degree angles) relative to the z-axis of the scanner using 3 imaging techniques (120-kV tube voltage using a medium convolution kernel, 120-kV tube voltage using a convolution kernel for bone, and 140-kV tube voltage using a convolution kernel for bone). Statistical analysis involved F test with a statistical significance of P < 0.05. Results: The convolution kernel for bone made it easier to evaluate the stenosis inside the stents, although it increased the luminal inhomogeneity significantly (Bx Velocity and Express2, P < 0.005; Driver, P < 0.05). The luminal inhomogeneity tended to increase as the strut diameter and the weight per unit length increased. Using 120-kV tube voltage, the luminal inhomogeneity inside the stents was at the minimum in the angle of 0 degree relative to the z-axis, and at the maximum in the angle of 90 degrees, except for Driver. The 140-kV tube voltage was effective for the improvement of luminal inhomogeneity and visibility of in-stent stenosis compared with the 120-kV tube voltage. Conclusions: The in-stent visibility of coronary stents on CT angiography can be improved by the use of 140-kV tube voltage with the convolution kernel for bone.

Postsurgical Intrahepatic Portal Thromboembolism: A Possible Cause of Perfusion Defects on Ct during Arterial Portography

Objective Our goal was to investigate unexplained nontumorous perfusion defects on CT arterial portography (CTAP). Materials and Methods The CTAP images of 35 patients who underwent partial hepatectomy or open biopsy were analyzed. Hepatic tumors consisted of hepatocellular carcinoma (n = 18) and colorectal carcinoma metastases (n = 17). Nontumorous perfusion defects were categorized into those previously explained and those unexplained. We investigated unexplained ones and their relationship with the underlying conditions. Results Eight unexplained nontumorous perfusion defects were found in four patients with colorectal metastases. Statistical analysis showed that the defects occurred with significantly higher incidence in patients with colorectal metastases than in those with hepatocellular carcinoma (p = 0.046, Fisher test). All four patients with defects underwent CTAP within 1 month after colorectal surgery. A significant difference was seen in the distribution of surgery-CTAP time intervals between those patients with and those without defects (p < 0.05, Wilcoxon-Mann-Whitney test). Intrahepatic portal thrombi were pathologically proven in one of the four patients.Conclusion: Unexplained nontumorous hepatic perfusion defects tnay represent postsurgical portal thromboemboli. Index Terms Colon, neoplasms—Liver—Liver, blood supply—Liver, neoplasms—Angiography—Computed tomography.

Partial splenic embolization with Y-shaped silicone particles

We have developed an embolizing material consisting of Y-shaped silicone particles for partial splenic embolization. Wide spaces for blood flow are left around the particles when these are lodged in arterial branches. We embolized one kidney in each of 3 dogs with the particles and observed a slowly induced occlusion of renal arterial branches during one month. The particles were also used for partial splenic embolization in 14 patients. The average portion of infarcted spleen tissue 7 days after embolization was 51% calculated from CT images. In 6 patients who had CT both 2 and 7 days after embolization, the average rate of splenic infarction increased from 29% at 2 days to 60% at 7 days. Our patients required analgesics for only 2.3 days on average. The Y-shaped silicone particles by slowly occluding splenic arterial branches produce ischemia in a gradual fashion which may minimize the pain after embolization.