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Biomedical subjects

T Kokubo

Publications and source records attributed to T Kokubo.

At least 289 records · Page 16Linked to original sources
PubMed1987

Aging test and dynamic fatigue test of apatite-wollastonite-containing glass ceramics and dense hydroxyapatite.

The purpose of this study is to examine the changes in mechanical strength of two bioactive ceramics in living tissue. An aging test and dynamic fatigue test were performed using apatite-wollastonite-containing glass ceramics (A X W-GC) and dense hydroxyapatite (HA). Specimens (5 mm X 5 mm X 25 mm, abraded with No. 2000 Al2O3 powder) were implanted into subcutaneous tissue of rats for varying periods of time. The bending strength of aged samples was measured by the three-point loading method. The bending strength of A X W-GC was greater than that of HA (P less than 0.001). There was no reduction in bending strength for both A X W-GC and HA in living tissue. The n value of both A X W-GC and HA did not decrease significantly after implantation as assessed by the results of the dynamic fatigue test according to analysis of covariance. SEM-EPMA showed that Si and Mg contents decreased, Ca content did not change, while P content increased in the surface of A X W-GC. The area where x-ray intensity changed increased moderately after implantation. There were no changes in Ca and P at the interface between HA and soft tissue. In macroscopic and microscopic observations, specimens were found to be encapsulated with a thin layer of connective tissue. Foreign body giant cells, osteoblasts, or osteoclasts were not observed in the soft tissue. There was no bonding between ceramics and soft tissue.

Animals↗
PubMed1987

Bonding behavior between two bioactive ceramics in vivo.

The purpose of this study is to examine the chemical bonding mechanism between bioactive ceramics in vivo. Two experiments were performed. In the first experiment, rectangular specimens (5 mm X 5 mm X 25 mm) of apatite-wollastonite containing glass-ceramics (designated A.W-GC) were used. In the second experiment, plates (15 mm X 10 mm X 2 mm) of A.W-GC and three types of hydroxyapatite (designated HA) were used. The sintering temperature and porosity (%) of the three types of HA were 1200 degrees C (0.4%), 1000 degrees C (4.8%), and 800 degrees C (45%), respectively. In each experiment, two pairs of specimens of identical material, one bound with silk thread, the other not bound, were implanted subcutaneously into rats. In the first experiment, bonding of only bound specimens was observed at 3 and 6 months after implantation. The observation of interface by SEM-EPMA showed that a Ca-P-rich layer formed between the two specimens. In the second experiment, bonding of both bound and nonbound A.W-GC produced identical results 1 month after implantation. For HA sintered at 800 degrees C and 1000 degrees C, bonding was observed in every specimen. This phenomenon might be caused by the chemical change of hydroxyapatite occurring at different sintering temperatures. The Ca-P-rich layer was observed between two plates. These results suggest that self-repair of bioactive ceramic is possible under certain conditions.

Animals↗
PubMed1987

Hepatic tumors: dynamic MR imaging.

Thirty-six patients with hepatic tumors (28 hepatocellular carcinomas, seven cavernous hemangiomas, one metastatic tumor) were examined with serial magnetic resonance (MR) imaging, after a bolus intravenous injection of 0.05 mmol/kg gadolinium-diethylenetriaminepentaacetic acid. A typical MR imaging pattern for hemangiomas (present in five of seven cases [71.4%]) was a lesion of diminished signal intensity on precontrast images, peripheral contrast enhancement during the bolus dynamic phase, and complete fill-in of high signal intensity on delayed scan images. Twenty-eight hepatocellular carcinomas showed a variety of contrast enhancement patterns during the dynamic phase. In 21 patients (75%), there was no area of high signal intensity within the tumor on the delayed phase. A peripheral halo with delayed enhancement was noticed in 12 patients (42.8%) Histologic correlation in hepatocellular carcinomas showed that the degree of contrast enhancement corresponded to tumor vascularity and that the peripheral halo corresponded to fibrous capsular structure.

Carcinoma, Hepatocellular↗
PubMed1987

Mucin-hypersecreting carcinoma of the pancreas.

Five cases of prominent, diffuse dilatation of the main pancreatic duct caused by mucin-hypersecreting carcinoma are reported. Adenocarcinoma was noted mainly within one markedly dilated main pancreatic duct. On endoscopic retrograde pancreatograms, dilated main pancreatic ducts with amorphous or well-defined filling defects resulting from mucin (five patients) or tumor (one patient) were noted. The proximal portion of the main pancreatic duct alone was delineated in three cases because of reflux of contrast material as a result of the presence of excessive mucin and a patulous orifice of the papilla of Vater (major duodenal papilla). Diffuse dilatation of the main pancreatic duct was demonstrated or suggested on computed tomographic (CT) and ultrasound scans. Four patients who underwent operations are alive and free from carcinoma (mean, 50 months after diagnosis). Whenever prominent, diffuse dilatation of the main pancreatic duct is encountered on CT or ultrasound scans, endoscopic retrograde pancreatography is mandatory to permit confirmation or ruling out of mucin-hypersecreting carcinoma of the pancreas.

Adenocarcinoma↗
PubMed1987

Regenerating nodules of liver cirrhosis: MR imaging.

A large number of tiny (0.5-1.5 cm), low-intensity nodules of the liver were retrospectively observed on T2-weighted magnetic resonance (MR) images of eight patients with cirrhosis of the liver. The lesions were not detected with other imaging modalities and were considered to be regenerating nodules. Twenty-five consecutive cases of liver cirrhosis referred for MR examination were prospectively investigated to study the detectability of regenerating nodules and the optimal pulse sequence for detection. A large number of small, low-intensity nodules were demonstrated in nine of 25 cases on T2-weighted spin-echo (SE) images, in nine of 22 cases on T1-T2 complex fast low-angle shot (FLASH) images, and in one of eight cases on T1-weighted SE images. FLASH images obtained with respiratory suspension most clearly revealed regenerating nodules. However, T2-weighted SE images clearly permit differentiation of high-intensity hepatocellular carcinoma, including small daughter lesions, from low-intensity regenerating nodules.

Aged↗
PubMed1987

Retained surgical sponges: CT and US appearance.

The computed tomographic (CT) and ultrasonographic (US) appearances of retained surgical sponges are described. In each case, the presence of a sponge was confirmed at repeat operation. CT examinations were performed in nine patients. In six cases, a low-density mass was demonstrated; in two cases, a complex mass with areas of both low and medium density was seen. The remaining case was a high-density mass. After intravenous administration of contrast material, dense and prolonged enhancement of the rim of the mass was noted in five of eight cases. Calcification was found in four cases, and spongiform gas in one. US performed in six patients revealed an echogenic area with strong acoustic shadowing in three cases and a complex mass, a hypoechoic mass, and a cystic mass with irregular internal echoes in one case each. Granuloma caused by a retained surgical sponge should be considered as a cause of an abdominal mass in patients with a history of prior abdominal surgery.

Abdomen↗
PubMed1987

Magnetic resonance imaging and histopathology in femoral head necrosis.

We correlated preoperative magnetic resonance (MR) images and histopathology of eight femoral heads from patients with osteonecrosis. The signal intensity of the MR image was low in the area where fibrovascular tissue, disintegrated fibrovascular tissue, or amorphous necrotic material occupied the medullary space. On the other hand, the necrotic marrow without revascularization showed high signal intensity. Osteonecrosis can be detected by MR imaging as soon as a certain amount of bone marrow is replaced by fibrovascular tissue.

Adult↗
PubMed1987

Hepatic haemangioma: dynamic MRI using gadolinium-DTPA.

Six patients with hepatic haemangioma were examined with a 1.5 tesla magnetic resonance scanner before and immediately after bolus injection of 0.05 mmol/kg gadolinium-DTPA. Eight to ten spin-echo images (TR: 100 msec, TE: 20 msec, scanning time: 26 sec) were obtained through the region of the haemangioma. In all cases, dense contrast enhancement of the lesion was demonstrated. The enhancement spread in all directions from the lesion on subsequent delayed scans (high signal fill-in); a signal higher than that from surrounding hepatic parenchyma was present two minutes after contrast injection. Dynamic MRI is a promising method for the evaluation of hepatic haemangioma and it is more easily tolerated by patients than dynamic CT using iodinated contrast medium.

Adult↗
PubMed1986

Carcinogenicity study of sodium hypochlorite in F344 rats.

The carcinogenic potential of sodium hypochlorite was examined in F344 rats. Groups of 50 males or 50 females were given sodium hypochlorite in their drinking-water, at concentrations of 0.1 and 0.05% for males and 0.2 and 0.1% for females, for 104 wk. Similar numbers of male and female rats received distilled water without supplement throughout the experiment. All surviving rats were killed at wk 112 (after 8 wk on untreated tap-water). Rats of both sexes given the chemical showed a reduction in body-weight gain, but haematological and biochemical examination of the blood showed no changes due to treatment, and no significant lesions attributable to the treatment were detected in any tissue in the histopathological investigation. Although a variety of tumours developed in all groups, no dose-related change in either the incidence or latent period of tumours was observed for any organ or tissue in either sex. Under the experimental conditions described, therefore, sodium hypochlorite was not carcinogenic in F344 rats.

Animals↗
PubMed1986

"Ductectatic" mucinous cystadenoma and cystadenocarcinoma of the pancreas.

Five cases of localized cystic dilatation of a side branch of the main pancreatic duct due to a new entity ("ductectatic" mucinous cystadenoma and cystadenocarcinoma) are reported. The dilated duct was widely covered by epithelium indistinguishable from that of mucinous cystadenoma (n = 4) or cystadenocarcinoma (n = 1) of the pancreas. All lesions were located in the uncinate process and were about 3 cm in size. On computed tomographic scans and sonograms, lesions were difficult to distinguish from simple cyst of the pancreas unless lobulated or irregular margins were demonstrated. Endoscopic retrograde pancreatography (ERP) or operative pancreatography clearly demonstrated characteristic findings: localized, prominent cystic dilatation of a side branch of the main pancreatic duct with grape-like clusters or pear-shaped pools of contrast material associated with filling defects of various sizes. When a cystic lesion is noted in the uncinate process of the pancreas, ERP is mandatory to confirm or rule out this potentially or overtly malignant disease.

Aged↗
PubMed1986

Dynamic CT features of arterioportal shunts in hepatocellular carcinoma.

Dynamic computed tomographic (CT) findings of 42 patients with hepatocellular carcinoma having angiographically proven arterioportal shunt were reviewed. CT findings related to arterioportal shunt were as follows: early enhancement of the portal vein, which showed a time-density curve similar to that of the aorta, markedly prolonged enhancement of the portal vein, dilated, abnormal intrahepatic vessels often accompanied by irregular, transiently enhanced areas, transient high attenuation of lobar or segmental distribution in the lobe contralateral to the main tumor, and transient wedge-shaped enhancement peripheral to the tumor. Dynamic CT usually detected arterioportal shunts involving larger portal veins as represented by any of the first four findings (14 of 17), whereas detection of arterioportal shunts involving smaller portal veins was lower in frequency (8 of 25), but such a shunt could be demonstrated as transient wedge-shaped enhancement peripheral to the tumor.

Arteriovenous Malformations↗
PubMed1986

CT of hepatic masses: significance of prolonged and delayed enhancement.

Hepatic masses showing higher density than that of liver after 3 min (prolonged enhancement) and/or having prominent enhancement after the arterial-dominant phase (delayed enhancement) of dynamic CT (bolus enhancement followed by serial scans) were reviewed. Prolonged enhancement was noted in any hepatic masses, but mainly in cavernous hemangioma and capsule of hepatocellular carcinoma, whereas delayed enhancement occurred in capsule of hepatocellular carcinoma and occasionally in metastatic tumor. The volume of arterial and portal blood supply, turnover rate of blood, extent of the interstitial space, and diffusion rate between the vascular and interstitial space, as well as dose and speed of contrast agent administered, seemed to be important factors in such contrast enhancement. Prolonged enhancement and delayed enhancement are nonspecific but still are of some value in the differentiation of hepatic masses on dynamic CT.

Biliary Tract Neoplasms↗