Biomedical subjects

Shigeru Sase

Publications and source records attributed to Shigeru Sase.

8 recordsLinked to original sources

PubMed2006

Determination of gate-on and -off timing in respiration-gated radiotherapy.

The purpose of this study was to develop an efficient method of determining gate-on and -off timing in respiration-gated radiotherapy. Gate-on and -off timing in a breathing cycle were defined as the respiratory signal level for the start of irradiation (Ls) in the expiration phase and that for the end of irradiation (Le) in the inspiration phase, respectively. Thirty subjects participated in this study. The diaphragm was used as the tracking target, and time-dependent changes in the position of the target were measured together with those in the respiratory signal level. For each subject, the following maps were created by varying the combination of Ls and Le: absolute target displacement (ATD) map, relative target displacement (RTD) map, and gate-on duty cycle (GDC) map. By classifying respiratory signal waveforms, three respiratory types were derived (A: the length of end-expiration level >40% of a breathing cycle, B: the length of end-expiration level 20% of a breathing cycle, and C: the length of end-expiration level <or=40% and that of end-inspiration level <or=20% of a breathing cycle). For each respiratory type, average RTD and GDC maps were created. We presented an algorithm to obtain the optimal Ls and Le using the RTD (or ATD) and GDC maps, and this algorithm was verified by demonstrating that, in determining Ls and Le for a subject, the average RTD and GDC maps corresponding to the subject's respiratory type could be used effectively.

Adult↗

PubMed2005

Prospective respiratory-triggered multidetector row CT (MDCT) for abdominal examinations: initial experience with a prototype.

PURPOSE: To develop a prototype for prospective respiratory-triggered multidetector row computed tomography (MDCT) for abdominal examinations and to assess its feasibility. MATERIALS AND METHODS: The prototype consisted of the following components: an MDCT unit, personal computer (PC), and a respiratory motion detector in the form of a wearable belt with sensors to measure differences in pressure caused by breathing excursions. The registered signals were processed by the PC. The abdominal MDCT images of 10 healthy volunteers were obtained with an incremental axial technique in the expiration phase during normal breathing. Multiplanar reformations (MPR) were then performed. On the basis of the precision of these reconstructions, two radiologists then assessed the accuracy and applicability of the system. RESULTS: Coronal and sagittal MPR images from these prospective respiratory-gated examinations were found to be accurate. In particular, the continuity of borders and surfaces of scanned organs proved the exactness of the previously acquired respiration-correlated axial source images. CONCLUSION: This prototype is feasible to perform prospective respiratory-triggered abdominal MDCT examinations during normal respiration without breathhold. This system may be useful for patients with reduced compliance in holding their breath.

Artifacts↗

PubMed2004

Xenon-inhalation computed tomography for noninvasive quantitative measurement of tissue blood flow in hepatocellular carcinoma.

OBJECTIVE: The purpose of this study was to separately measure the arterial and portal venous tissue blood flow (TBF) of hepatocellular carcinoma (HCC) with a noninvasive method using xenon inhalation CT (xenon-CT) and to differentiate between well-differentiated HCCs and moderately and poorly differentiated HCCs. MATERIALS AND METHODS: Total, arterial and portal venous TBFs of 38 surgically proven HCC nodules from 38 patients were measured by means of xenon-CT. Serial abdominal CT scans were obtained before and after inhalation of nonradioactive xenon gas. TBF was computed using the Fick principle, after which the correlation between TBF and pathologic features of the tumors was determined. RESULTS: Total, arterial, and portal venous TBFs of HCC were 125.7 +/- 59.9 mL/min/100g, 102.5 +/- 37.3, and 22.2 +/- 11.4, respectively, and the corresponding findings for hepatic parenchyma were 67.3 +/- 13.1, 25.2 +/-9.6, and 42.4 +/- 11.0. Total and arterial TBFs of HCC were significantly higher than those of the hepatic parenchyma (P < 0.01), whereas portal venous TBF of HCC was significantly lower than that of hepatic parenchyma (P < 0.01). Arterial TBF of moderately or poorly differentiated HCC (120.4 +/- 38.2) was significantly higher than that of well-differentiated HCC (60.4 +/- 43.5) (P < 0.01). CONCLUSIONS: Arterial and portal venous TBFs of HCC could be measured separately, noninvasively, and safely with xenon-CT. Correlation between TBF and pathologic features of tumors indicate that xenon-CT can be used to differentiate between well-differentiated HCCs and moderately and poorly differentiated HCCs.

Adult↗

PubMed2003

Noninvasive quantitative measurement of tissue blood flow in hepatocellular carcinoma using xenon-enhanced computed tomography.

The aim of this study was to quantitatively measure tissue blood flow (TBF) in hepatocellular carcinoma (HCC) by a noninvasive method using xenon (Xe) inhalation/CT scans and to correlate the measured TBF with histological features. TBF was measured in HCC with xenon-enhanced CT (xenon/CT) in 20 patients. In 15 patients with HCC diagnosed as hypervascular tumors by conventional CT, TBF of the tumors was significantly higher than that of noncancerous liver tissue (151.1 +/- 20 vs 42.6 +/- 20 ml/min/100 g). Histologically, these tumors were diagnosed as moderately-to-poorly differentiated HCC. In contrast, in five patients with hypovascular HCC, TBF of HCC was almost comparable to that of the noncancerous regions (45.3 +/- 6 vs 48.3 +/- 6 ml/min/100 g). All these tumors were well-differentiated HCC. In conclusions, the measured values of TBF correlate with the clinicopathologic features of liver tumors and nontumorous liver tissue in patients with HCC.

Administration, Inhalation↗

PubMedDate not supplied

Hepatic blood flow measurements with arterial and portal blood flow mapping in the human liver by means of xenon CT.

PURPOSE: The purpose of this work was to quantify arterial and portal blood flows in the human liver and to create blood flow maps by means of xenon CT. METHOD: Mathematical procedures were developed based on a simplified model having two tissue components: liver tissue and portal organ tissue. Xe-CT studies were performed on 10 healthy volunteers (ages 33.4 +/- 9.8 years), a patient with hepatocellular carcinoma (HCC), and a liver transplant recipient. RESULTS: Arterial and portal blood flows for the healthy subjects were 36.7 +/- 5.2 and 65.2 +/- 22.0 ml/100 ml/min. In the HCC patient, arterial blood flow was shown to be dominant in the tumoral area. From the results of the liver recipient, it was demonstrated that obtaining lambda values is important for proper evaluation of blood flows. CONCLUSION: Xe-CT can provide substantial information on hepatic blood flow quantitatively and visually with separation of arterial and portal components.

Adult↗

PubMedDate not supplied

Quantitative cerebral blood flow calculation method using white matter lambda in xenon CT.

The objective of this work is to propose a quantitative cerebral blood flow (CBF) calculation method for xenon CT (Xe-CT) by logically estimating the time course change rate (rate constant) of the arterial xenon concentration from that of end-tidal xenon concentration. A single factor, gamma (gamma), which is considered to reflect the diffusing capacity of the lung for xenon, was introduced to correlate the end-tidal rate constant (Kend-tidal) with the arterial rate constant (Karterial). When an appropriate value is given to gamma, it is possible to calculate the arterial rate constant (calculated Karterial) from Kend-tidal. A procedure was developed to determine the gamma value utilizing the characteristics of white matter lambda (lambda). This procedure was applied to three healthy volunteers. The gamma gammaalues for the three subjects were consistent with those directly calculated from end-tidal and arterial (abdominal aorta) xenon data. Hemispheric CBF values with use of calculated Karterial (47.3 +/- 10.3 ml/100 g/min) were close to the reported normative values. We conclude this method could make current Xe-CT examinations substantially reliable and quantitative in measuring CBF.

Adult↗

PubMedDate not supplied

Quantitative multilevel mapping of hepatic blood flow by xenon computed tomography using aorta.

A noninvasive and quantitative technique has been developed to measure human hepatic blood flow by xenon computed tomography (Xe-CT). Accurate data on time-dependent xenon concentrations in the arterial blood are indispensable for Xe-CT to ensure quantitativeness of measured blood flow. A method has been established by our group to use both aorta and end-tidal data to obtain arterial xenon information. Multilevel (3 levels) maps of arterial blood flow (Fa), portal blood flow (Fp), and partition coefficient (lambda) were created for patients with chronic hepatitis. A method to objectively evaluate Fa, Fp, and lambda values for the whole liver has also been developed by our group.

Aorta↗

PubMedDate not supplied

Comparison of cerebral blood flow between perfusion computed tomography and xenon-enhanced computed tomography for normal subjects: territorial analysis.

OBJECTIVE: The purpose of this study was to clarify the difference between cerebral blood flow (CBF) by perfusion computed tomography (CT) and that by xenon-enhanced CT (Xe-CT) through simultaneous measurement. METHODS: Xenon-enhanced CT and perfusion CT were continually performed on 7 normal subjects. Ratios of CBF by perfusion CT (P-CBF) to CBF by Xe-CT (Xe-CBF) were measured for 5 arterial territories; 3 were territories of 3 major arteries (the anterior [ACA], middle [MCA], and posterior [PCA] cerebral arteries), and the other 2 were areas of the thalamus and putamen. RESULTS: The ratios were 1.30 +/- 0.10, 1.26 +/- 0.15, 1.61 +/- 0.15, 0.801 +/- 0.087, and 0.798 +/- 0.080 for the ACA, MCA, PCA, thalamus, and putamen, respectively. Although a good correlation was observed between P-CBF and Xe-CBF for each territory, the ratios were significantly different (P < 0.0001) between 3 territory groups (group 1: ACA and MCA, group 2: PCA, and group 3: thalamus and putamen). CONCLUSIONS: The difference in the ratio of P-CBF to Xe-CBF between the 3 territory groups was considered to result principally from the features of P-CBF. To evaluate P-CBF properly, its territorial characteristics should be taken into account.

Adult↗