Biomedical subjects

Y Sakamoto

Publications and source records attributed to Y Sakamoto.

976 records · Page 55Linked to original sources

PubMedDate not supplied

Value of magnetization transfer contrast in intracranial enhancing and nonenhancing lesions with paramagnetic contrast agents.

PURPOSE: To evaluate normal brain structures and various brain lesions by magnetic resonance (MR) imaging with magnetization transfer (MT) under the use of paramagnetic contrast agents. METHODS: T1-weighted MR images were obtained before and after the administration of gadopentetate dimeglumine with and without MT in 125 lesions of 61 patients. Normal brain structures and various brain lesions were evaluated by means of MT ratios (MTR) and contrast-to-noise ratios (C/N). RESULTS: Among normal structures, the white matter had a larger MTR than the gray matter, and no significant difference in MTRs was noted between pre- and postcontrast T1-weighted images. The MTRs were smaller in both enhancing and nonenhancing lesions than in the white matter. For most enhancing lesions, the MT technique increased the C/N on postcontrast images, whereas it decreased them on precontrast images. Improvement in C/N was observed on precontrast images in some gliomas as well as white matter lesions such as tuberous sclerosis and multiple sclerosis. CONCLUSION: The MTC method improves conspicuity and detection of intracranial enhancing lesions with use of paramagnetic contrast agents. Although the MTC method does not replace the conventional method, it is useful for detecting small enhancing lesions and for evaluating some nonenhancing lesions.

Adolescent↗

PubMedDate not supplied

Determination of the optimal pulses in MR imaging with magnetization transfer contrast at 7 Tesla.

OBJECTIVE: The magnetization transfer contrast (MTC) effect depends on the shape, duration, amplitude, and offset frequency of the saturation pulse. In the present study, we investigated optimal combinations of these four parameters in vitro. METHODS: All experiments were performed with a 7.05 Tesla MR system, and the spin echo technique (TR 500/TE 30) was adopted. We used a simple phantom composed of 1% agar and water, representing restricted and free proton pools, respectively. Signal intensity changes were measured in the agar (Ma) and water (Mw), when the shape, duration, magnitude, and offset frequency of the saturation pulses were varied. The MTC effect was examined with the Mw/Ma ratio. RESULTS: The suppression of Mw was less with the gauss pulse than with the square and sinc pulses. The gauss pulse had the best MTC effect. The suppression of both Ma and Mw was greatest with a saturating duration of 60 msec. The MTC effect was greatest with a longer saturation pulse. The larger the amplitude, the stronger the MTC effect obtained. Mw was suppressed with an offset frequency of less than 3 kHz, and the MTC effect was greatest with an offset frequency closer to the spectrum of the free proton pool. CONCLUSION: In the present study the optimal MTC pulse at 7 Tesla is the gauss pulse with longer duration, maximal amplitude, and approximately 3 kHz off resonance.

Contrast Media↗

PubMedDate not supplied

Selective and unselective clamping in cirrhotic liver.

BACKGROUND/AIMS: Liver surgery requires a reduction of the operative blood loss especially for patients with cirrhosis. Selective or unselective liver clamping during hepatic resection is performed to minimize the surgical risk for such compromised patients. METHODOLOGY: We carried out elective hepatic resection in 158 patients with the use of total hilar clamping (Pringle's manoeuvre) or selective vascular clamping (Makuuchi's manoeuvre). The clinical outcomes were evaluated according to the clamping method and the condition of background liver. RESULTS: Pringle's manoeuvre was used in 132 patients who underwent all types of hepatectomy, whereas Makuuchi's manoeuvre was applied selectively to 26 patients, most of whom underwent segmentectomy or subsegmentectomy. A modified Makuuchi's manoeuvre was used in eight healthy donors who underwent left-sided hepatectomy for transplantation. The cumulative clamping times and blood losses were 61 +/- 47 min (mean +/- SD) and 831 +/- 716 ml in the Pringle's manoeuvre group, and 95 +/- 47 min and 1.035 +/- 577 ml in the Makuuchi's manoeuvre group. In patients with normal hepatic parenchyma the longest clamping time was 322 min, and in those with cirrhosis it was 202 min. All the patients in this series tolerated vascular clamping well, and their hepatic functional parameters returned, regardless of the presence or absence of cirrhosis, to the baseline levels within a week. As a whole, the operative morbidity and mortality rates were 20.3% and 0%, respectively. CONCLUSIONS: Intermittent total or selective clamping can be an indispensable procedure during hepatic resection for all patients, irrespective of the degree of hepatic dysfunction, to improve safety and resectability.

Blood Loss, Surgical↗

PubMedDate not supplied

A new porto-systemic bypass technique for hepatopancreatoduodenectomy with portal vein resection.

When reconstructing the portal vein (PV) following hepatopancreatoduodenectomy (HPD) with PV resection, a new porto-systemic bypass (PSB) technique can be employed to prevent intestinal vascular congestion. The Whipple procedure is performed in a standard manner, as long a portion of the gastrocolic trunk is preserved for insertion of an antithrombogenic catheter (ATC). After harvesting the left external iliac vein and exposing the right great saphenous vein, the end of the ATC is inserted in the superior mesenteric vein via the gastrocolic trunk in the distal direction and the other end of the ATC is inserted in the greater saphenous vein. PSB is achieved as a result of the venous pressure gradient. By employing this technique, an ATC can be inserted without damaging another mesenteric venous branch and with minimal damage to the endothelium, and the small intestine is not exposed in the operative field until enteric reconstruction is started. This technique is a promising option for PSB during HPD with PV resection.

Catheterization↗