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Biomedical subjects

H Toyama

Publications and source records attributed to H Toyama.

At least 19 recordsLinked to original sources
PubMed1992

Quantitative phase analysis of myocardial wall thickening by technetium-99m 2-methoxy-isobutyl-isonitrile SPECT.

Regional wall thickening was assessed by ECG-gated SPECT using technetium-99m 2-methoxy-isobutyl-isonitrile (99mTc-MIBI). For myocardial segments with an optimal short axis, regional count changes from end-diastole to end-systole were used to calculate the regional wall thickening. Functional images displaying amplitude, % wall thickening (% WT), and phase were generated by a fundamental Fourier analysis. In the control subjects, % WT analysis showed heterogeneous contraction among the left ventricular wall segments. The amplitude values showed a similar pattern to the %WT values. Phase images demonstrated that the timing of ventricular contraction was almost homogenous between the various wall segments. In the CAD patients, regional decreases in amplitude and %WT corresponding to zones of reduced perfusion were shown in the ischemic segments. Phase images also indicated asynchronous contraction in these segments. Phase analysis of regional wall thickening in 99mTc-MIBI scintigraphy seems to be useful for understanding regional myocardial function in combination with perfusion scanning.

Aged↗
PubMed1992

Perfusion and mechanical analysis with technetium-99m 2-methoxy-isobutyl-isonitrile in a case of dilated cardiomyopathy.

With technetium-99m 2-methoxy-isobutyl-isonitrile (99mTc-MIBI), regional wall thickening in a patient with dilated cardiomyopathy was analyzed by the first component Fourier method. The regional wall thickening was compared with thallium-201 and 99mTc-MIBI SPECT imaging. Thallium-201 SPECT images showed mildly reduced perfusion in the posterior wall and redistribution in the septum, whereas 99mTc-MIBI images showed heterogeneous accumulation around the left ventricular circumference. By means of phase analysis, diffusely decreased wall thickening and discontinuity of percent wall thickening in neighboring segments were observed throughout the left ventricle. Regional wall motion and wall thickening correlated roughly. However, discrepancies between the mechanical function and myocardial perfusion, and discrepancies in regional myocardial perfusion between thallium-201 and 99mTc-MIBI were observed.

Aged↗
PubMed1992

'Reverse crescent pattern' on SPECT brain perfusion scan in chronic subdural hematoma.

A SPECT brain perfusion scan was performed on a patient who had symptoms of dementia. The SPECT scan showed marked crescentic medial displacement of the left cerebral hemisphere ("reverse crescent pattern"), and mildly decreased cortical perfusion in the affected hemisphere. Crossed cerebellar diaschisis was not present. On x-ray CT, the underlying abnormality was found to be a unilateral chronic subdural hematoma causing a significant mass effect. A reverse crescent pattern without crossed cerebellar diaschisis on SPECT brain perfusion scan in patients with dementia may suggest the diagnosis of chronic subdural hematoma.

Aged↗
PubMed1992

Neuroanatomical localization for clinical SPECT perfusion brain imaging: a practical proportional grid method.

For the purpose of facilitating anatomical localization in interpretation of 99Tcm-hexamethylpropyleneamine oxime (HMPAO) brain single photon emission tomographic (SPECT) scans, a stereotaxic proportional grid system was applied in the form of an interactive computer program. This method takes advantage of a rotating gamma camera system which permits planar scout imaging for the determination of anatomical reference lines, and standardization of tomographic slices for brain size. Using measurements made on a lateral planar HMPAO image, proportional grids were constructed onto standardized transaxial images. This method was implemented for 33 clinical HMPAO SPECT studies. It required less than 15 min of an operator's time. This simple and practical neuroanatomical localization technique can be instrumental as an aid to the interpretation of routine clinical HMPAO SPECT images.

Adult↗
PubMed1992

Characterization of membrane-bound spermidine dehydrogenase of Citrobacter freundii.

Spermidine dehydrogenase found in the membrane fraction of Citrobacter freundii IFO 12681 was solubilized with Triton X-100 and further purified to homogeneity. The properties of the membrane enzyme were almost identical to those obtained from the soluble fraction of the organism with respect to molecular and catalytic properties. Thus, binding properties of the enzyme to the bacterial membrane were checked. The ratio of enzyme activity found in the soluble fraction to the membrane fraction was dependent on salt concentration during cell disruption. A hydrophobic interaction was largely involved in anchoring the enzyme to the membrane fraction. Purified spermidine dehydrogenase from the soluble fraction was readily adsorbed into the membrane fraction in the presence of salt. Spermidine dehydrogenase appeared to be a membrane-bound enzyme localized in the cytoplasmic membranes in a manner that makes a partial release of the enzyme possible during mechanical cell disruption. When spermidine oxidation was done with the resting cells of C. freundii, a stoichiometric formation of two reaction products, 1,3-diaminopropane and gamma-aminobutyraldeyde, was observed without any lag time. These facts indicate that the enzyme is localized on the outer surface of the cytoplasmic membranes or in the periplasmic space of the organism.

Amino Acids↗
PubMed1992

Evaluation of the effect of PTCR/PTCA by 99mTc-MIBI myocardial imaging in acute and old myocardial infarction.

This study is to clarify the ability of technetium-99m-Hexakis-2-methoxyisobutyl isonitrile(MIBI) myocardial scintigraphy for assessment of the effect of PTCR/PTCA as compared with conventional thallium-201 myocardial scintigraphy (201Tl). 99mTc-MIBI (740-888MBq) was injected before emergency PTCR/PTCA, and the initial imaging was performed immediately after PTCR/PTCA in 4 patients with acute myocardial infarction (AMI). On the other hand, in 2 patients with old myocardial infarction (OMI), 201Tl and MIBI myocardial imagings were performed before and one week after rescue PTCA. The defect area on the follow-up MIBI imaging was smaller than that on the initial MIBI imaging in 2 patients with successful emergency PTCR/PTCA. But in the other 2 AMI patients with unsuccessful reperfusion, the defect area did not significantly decrease after PTCR/PTCA. Reperfusion was successful in one of the two patients with OMI. In both the two patients with OMI, the MIBI defect area did not significantly decrease after rescue PTCA. MIBI myocardial scintigraphy is a useful noninvasive method for evaluating the effect of emergency PTCR/PTCA for myocardial salvage in patients with AMI, because MIBI is a kit type agent, and it does not redistribute.

Aged↗
PubMed1992

Quantitative measurement of regional cerebral blood flow using N-isopropyl-(iodine-123)p-iodoamphetamine and single-photon emission computed tomography.

We have developed a quantitative method of measuring regional cerebral blood flow (rCBF) by using N-isopropyl-(iodine-123)p-iodoamphetamine and single-photon emission computed tomography (SPECT). Twenty-five dynamic SPECT images (24 sec/scan) were collected immediately after tracer injection using a ring-type SPECT system and the accumulation curve (C(t)) was obtained. The time-activity curve corresponding to the arterial blood activity curve was used as B(t). The latter curve was calculated from the lung time-activity curve monitored during scanning and corrected by the actual activity obtained by one-point blood sampling 5 min after tracer injection. The octanol extraction ratio during scanning was considered to be constant and taken as the value measured 5 min after tracer injection (E). The uptake constant (K) per pixel was calculated by the least squares fitting method as the slope of the linear relationship in which C(t)/E x B(t) was plotted against E x integral of t(o)B(tau)d tau/E x B(t). Functional maps of rCBF values were obtained on a 64 x 64 matrix by calculating the uptake constant per pixel and the cross calibration factor (CF) between the SPECT system and a well counter (rCBF = K.CF x 100).

Adult↗
PubMed1991

Thermostable alanine racemase of Bacillus stearothermophilus. Construction and expression of active fragmentary enzyme.

Limited proteolysis studies on alanine racemase suggested that the enzyme subunit is composed of two domains (Galakatos, N. G., and Walsh, C. T. (1987) Biochemistry 26, 8475-8480). We have constructed a mutant gene that tandemly encodes the two polypeptides of the Bacillus stearothermophilus enzyme subunit cleaved at the position corresponding to the predicted hinge region. The mutant gene product purified was shown to be composed of two sets of the two polypeptide fragments and was immunologically identical to the wild-type enzyme. The mutant enzyme, i.e. the fragmentary alanine racemase, was active in both directions of the racemization of alanine. The maximum velocity (Vmax) was about half that of the wild-type enzyme, and the Km value was about double. Absorption and circular dichroism spectra of the fragmentary enzyme were similar to those of the wild-type enzyme. An attempt was made to separately express in Escherichia coli a single polypeptide corresponding to each domain, but no protein reactive with the antibody against the wild-type alanine racemase was produced. Therefore, it is suggested that the two polypeptide fragments can fold into an active structure only when they are co-translated and that they correspond to structural folding units in the parental polypeptide chain.

Alanine Racemase↗
PubMed1991

A study of ventricular contraction sequence in complete right bundle branch block by phase analysis.

Twenty-four patients with complete right bundle branch block (CRBBB) combined with and without left axis deviation (LAD) on ECG, were compared with 17 normal subjects to evaluate the right ventricular contraction sequence and pattern in detail. Blood pool scintigrams were obtained in the left anterior oblique projection, and these images were analyzed by first component Fourier harmonics. In the normal subjects, the phase value distribution representing the pattern of ventricular contraction was almost homogeneous in both the right and left ventricles (RV & LV). In the CRBBB patients without LAD, the phase images showed apparent phase delay in the right ventricle. In the CRBBB patients with LAD, the phase images showed many different contraction patterns varying from normal to RV phase delay, owing to the effects of the hemi-block. Quantitative analysis of the absolute values, showed that the mean (RV-LV) value was 6.6 +/- 8.4 msec in the normal subjects. In the CRBBB patients without LAD, the duration of the QRS complex correlated with the mean (RV-LV) value, whereas no difference was observed between the duration of the QRS complex and the standard deviation of the right ventricle. Using phase analysis the degree of the RBBB can be determined from the phase images, and can be quantitatively analyzed as in electrical studies.

Adult↗
PubMed1991

Quantitative measurement of regional cerebral blood flow with I-123 IMP SPECT: a correction of the microsphere model by global extraction between artery and internal jugular vein.

Quantitative measurements of regional cerebral blood flow with N-isopropyl-(Iodine 123)p-iodoamphetamine (I-123 IMP) as a microsphere model were performed in forty cases. The regional cerebral blood flow values obtained with I-123 IMP were slightly underestimated compared with those of Xe-133 inhalation methods (y = 0.90x-2.1, r = 0.85, p less than 0.01). After correction by global extraction (87%) between the artery and internal jugular vein, which was measured in four patients by means of a catheter technique, the underestimation of the values obtained with I-123 IMP was improved (y = 1.0x-2.4, r = 0.85, p less than 0.01). Several problems in the accurate quantitative measurement of regional cerebral blood flow with I-123 IMP are discussed.

Adult↗
PubMed1991

Thermostable alanine racemase of Bacillus stearothermophilus: subunit dissociation and unfolding.

The guanidine hydrochloride-induced subunit dissociation and unfolding of thermostable alanine racemase from Bacillus stearothermophilus have been studied by circular dichroism, fluorescence and absorption spectroscopies, and gel filtration. The overall process was found to be reversible: more than 75% of the original activity was recovered upon reduction of the denaturant concentration. In the range of 0.6 to 1.5 M guanidine hydrochloride, the dimeric enzyme was dissociated into a monomeric form, which was catalytically inactive. The monomeric enzyme appeared to bind the cofactor pyridoxal phosphate by a non-covalent linkage, although the native dimeric enzyme binds the cofactor through an aldimine Schiff base linkage. The monomer was mostly unfolded, with the transition occurring in the range of 1.8 to 2.2 M guanidine hydrochloride.

Alanine Racemase↗
PubMed1991

[Effects of aging on right and left ventricular function in patients with right bundle branch block].

The effect of aging on cardiac function in patients with right bundle branch block (RBBB) was commonly unknown, so left ventricular function and right ventricular function were investigated, using first-pass radionuclide angiography. Twenty-six patients with RBBB and 28 normal subjects were studied at rest and during bicycle exercise. Patients with RBBB but normal cardiovascular systems aged 33 to 75 years were divided into those within 60 years (n = 17) and those over 65 years (n = 9). Using the same method, normal subjects aged 38 to 83 years were divided into those within 60 years (n = 18) and those over 65 years (n = 10). Mean age between normal subjects and patients with RBBB didn't differ significantly. The response of left ventricular ejection fraction in normal groups rose during exercise, but its exercise tolerance function declined with aging. Left ventricular diastolic filling in normal groups declined at rest and during exercise with aging. Left ventricular function in RBBB groups showed the same results as those of normal groups. The response of right ventricular ejection fraction and its exercise tolerance function in normal groups was not influenced by aging. However, in contrast, right ventricular function in RBBB groups decreased with aging. We suggest that the mechanism of decrease of right ventricular function in aging patients with RBBB may be caused by the change of right ventricular contraction which is affected by the aging process.

Adult↗
PubMed1991

[A study on crosstalk correction in dual energy acquisition of 123I-MIBG and 201TlCl in myocardial SPECT].

In the simultaneous dual energy acquisition, energy spectrums of two radionuclides crosstalk each other and this phenomenon is a cause of the poor quality of images. In order to obtain the image of high quality in dual energy acquisition of 123I-MIBG and 201TlCl, a crosstalk correction method was originated. The crosstalk from 201Tl to 123I window (R1) and the crosstalk from 123I to 201Tl window (R2) were determined by the cardiac phantom studies. R1 and R2 showed almost constant value throughout the myocardial wall. The crosstalk correction was performed using R1 and R2. After the crosstalk correction, the defect region placed in the cardiac phantom was detected more clearly both in visual interpretation and in quantitative analysis. The crosstalk correction method with R1 and R2 was applied to some clinical cases. By the crosstalk correction, the quality of image was improved and a false defect caused by crosstalk disappeared in a clinical case. The crosstalk correction was considered to be useful for improving the quality of image on dual energy acquisition.

3-Iodobenzylguanidine↗
PubMed1991

[The influence of the time activity variation on dynamic SPECT images in camera based SPECT].

Image quality of dynamic single photon emission computed tomography (SPECT) using a rotating gamma camera is dependent on the time activity variation of the tracer such as accumulation and excretion in the object's organ. Especially at the early time after injection of radionuclide, artifacts may occur strongly in the SPECT images. Simulated and experimental projection data of line sources and Jaszczak phantom were altered by sequentially weighting the projections with a function that varied linearly with time. With a variation of object activity given by linearly decaying functions, the main effect observed on the SPECT images obtained from simulated line sources was an elliptical deformation on the object. If the changing rate (R (t + 1)-R(t))/R(t) x 100 remained within 20% during acquisition, this deformation of SPECT images of line sources was not noticeable visually and resolution (FWHM) of line sources scarcely was degraded. In renal dynamic SPECT study using 99mTc-DTPA, the image quality of the first scan (30 sec) was considerably degraded. However, the changing rates after the third scan were less than 20% on the mean of 10 kidneys and the image quality was not noticeable visually.

Gamma Cameras↗
PubMed1990

[Variable threshold levels for estimation of renal uptake of 99mTc-dimercaptosuccinic acid based on single photon emission computed tomography].

To calculate renal uptake of 99mTc-dimercaptosuccinic acid (DMSA) more accurately using single photon emission computed tomography (SPECT), it is necessary to estimate values of threshold level, which corresponds to the ratio of kidney to background (BG ratio). Thus the phantom and clinical studies were conducted. Six kinds of renal phantoms of 80 to 339 ml, contained different radioactivity of 37 to 485 MBq were prepared. These phantoms were placed in a larger body phantom filled with 1 to 50% of radioactivity representing background. Clinical application of this method was also performed. Results were as follows. 1) A significant correlation between phantom volumes and estimated volumes obtained using threshold level based on BG ratio calculated on tomographic images was found (r = 0.99). 2) A significant correlation between total counts in estimated volumes and radioactivities in phantoms was recognized (r = 0.94). 3) Known radioactivity in phantoms and radioactivity in estimated volumes were highly related (r = 0.98). 4) Clinical application showed valuable results in patients with renal dysfunction. Thus, this method can calculate more accurate renal uptake of 99mTc-DMSA.

Adult↗
PubMed1990

Cerebral hemodynamics in patients with chronic obstructive carotid disease by rCBF, rCBV, and rCBV/rCBF ratio using SPECT.

To evaluate cerebral hemodynamics, 21 patients with chronic occlusion or severe stenosis of the internal carotid or middle cerebral artery with normal or only lacunar infarction on x-ray CT were studied using single photon emission computed tomography (SPECT). We measured rCBV with 99mTc erythrocytes after rCBF with 133Xe, and calculated rCBV/rCBF. rCBF and rCBV of the 25 affected hemispheres were classified as (a) patients with normal rCBF [type I (n = 7) and type II (n = 3)]; (b) patients with decreased rCBF [type III (n = 6) and type IV (n = 9)]. These two groups then could be subdivided according to findings of rCBV, normal, and increased blood volumes. rCBV/rCBF increased as the cerebral perfusion pressure dropped from type I to type III. In type IV, other situations but cerebral autoregulation could be assumed. rCBV/rCBF signifies vascular mean transit time. Type III (high rCBV/rCBF) assumed as the increased OEF, misery perfusion as reported in PET. We propose rCBF, rCBV and rCBV/rCBF using SPECT can be an index for cerebral circulatory reserve.

Arterial Occlusive Diseases↗
PubMed1990

[Two cases of superior mesenteric vein thrombosis; the utility of CT scan].

Two cases of superior mesenteric vein thrombosis were examined with computed tomography. Prior to the operation the CT appearances of the disease were, as follows: focal thickening of the bowel wall, gas and fluid collection in the dilated bowel, mesenteric leaf, a little ascites and dilated superior mesenteric vein with central filling defect. We conclude that CT scan is very useful for an early diagnosis of the superior mesenteric vein thrombosis.

Aged↗