Takao Mukai

SPECT with 99mTc]-d,l-Hexamethyl-Propylene Amine Oxime (HM-PAO) Compared with Regional Cerebral Blood Flow Measured by PET: Effects of Linearization

In order to validate the use of technetium-99m–d,l-hexamethylpropyleneamine oxime (HM-PAO) as a flow tracer, a total of 21 cases were studied with single photon emission computerized tomography (SPECT), and compared to regional cerebral blood flow (rCBF) measured by position emission tomography (PET) using the oxygen-15 CO2 inhalation technique. Although HM-PAO SPECT and rCBF PET images showed a similar distribution pattern the HM-PAO SPECT image showed less contrast between high and low activity flow regions than the rCBF image and a nonlinear relationship between HM-PAO activity and rCBF was shown. Based on the assumption of flow-dependent backdiffusion of HM-PAO from the brain, we applied a “linearization algorithm” to correct the HM-PAO SPECT images. The corrected HM-PAO SPECT images revealed a good linear correlation with rCBF (r = 0.901, p < 0.001). The results indicated HM-PAO can be used as a flow tracer with SPECT after proper correction.

Effects of coronary artery reperfusion on relation between creatine kinase-MB release and infarct size estimated by myocardial emission tomography with thallium-201 in man.

The quantitative relations between serum creatine kinase-MB isoenzyme (CK-MB) release and the final infarct size estimated by myocardial emission computed tomography with thallium-201 was assessed in 37 patients with a first acute transmural myocardial infarction who underwent intracoronary thrombolysis using urokinase 4.6 +/- 1.9 hours after the onset of symptoms. Serial CK-MB determinations were used to calculate the accumulated release of CK-MB (sigma CK-MB). Myocardial emission tomography with thallium-201 was performed 4 weeks after the onset, and infarct volume was measured from reconstructed tomographic images by computerized planimetry. The results are presented for two groups of patients: 11 patients with unsuccessful thrombolysis (group A) and 26 patients with successful thrombolysis (group B). An excellent linear relation was found for group A (sigma CK-MB = 6.4 X infarct volume + 47.7, r = 0.91), whereas a different linear relation was observed for group B (sigma CK-MB = 10.5 X infarct volume + 89.1, r = 0.80). Moreover, serum CK-MB activity reached a peak at 21.1 +/- 2.2 hours after the onset in group A and reached an earlier peak at 12.5 +/- 2.9 hours in group B (p less than 0.001). These data suggest that acute coronary recanalization alters the kinetics of CK-MB release, resulting in greater CK-MB release into the serum for equivalent infarct volume estimated by myocardial emission tomography with thallium-201. Thus, serum CK-MB time-activity curves after acute myocardial infarction may be influenced considerably by acute reperfusion, which is an important factor that should be incorporated in the interpretation of enzymatic estimates of infarct size in human patients.

Segmental analysis of stress thallium myocardial emission tomography for localization of coronary artery disease

The value of stress thallium 201 myocardial emission computed tomography (ECT) in the assessment of coronary artery disease (CAD) was analyzed in 75 patients admitted for coronary arteriography. The ECT provided contiguous transaxial, short-axis, and long-axis sections of the myocardium and the myocardial images were divided into nine segments. The sensitivity and specificity in the diagnosis of CAD were 95% and 93%, respectively. Using selected segments, the ECT identified 97 of 111 (83%) major vessels involved: 89% for right coronary artery (RCA), 88% for left anterior descending (LAD), and 70% for left circumflex (LCx). Among the 75 cases, 35 underwent stress conventional planar imaging within 3 months. The planar imaging provided high sensitivity (90%) and specificity (100%) for the detection of CAD patients as well, but it showed lower sensitivity (57%, P<0.001) in identifying individual vessels involved: 55% for RCA (P<0.01), 70% for LAD, and 36% for LCx (P<0.05). Stress ECT detected vessel involvement more in two-vessel disease (85%) and three-vessel disease (78%) than the planar imaging (50%: P<0.05 and 44%: P<0.01, respectively). Thus, segmental analysis of stress ECT yielded as high sensitivity and specificity in the diagnosis of CAD as the planar imaging. This can improve sensitivity in identifying individual vessels involved in deep myocardial regions, especially in those with multivessel disease.

Recognition of regional hypertrophy in hypertrophic cardiomyopathy using thallium-201 emission-computed tomography: Comparison with two-dimensional echocardiography☆

The configuration of the hypertrophied myocardium was evaluated by thallium-201 emission-computed tomography and 2-dimensional (2-D) sector scan in 10 patients with obstructive hypertrophic cardiomyopathy (HC), 10 with nonobstructive HC with giant negative T waves and 10 with concentric left ventricular (LV) hypertrophy. Thallium-201 myocardial imaging was reconstructed into multiple 12-mm-thick slices in 3 planes. The thickness ratio of the ventricular septum and the LV posterior wall in the short-axis plane and the ratio of the ventricular septum and the apical wall in the long-axis plane were analyzed. In the patients with obstructive HC the ventricular septal wall thickness index was increased, and the ratio of septal to posterior wall thickness index (1.45 +/- 0.23) was greater than that in the patients with nonobstructive HC with giant negative T waves or in those with concentric LV hypertrophy (1.03 +/- 0.20 and 0.98 +/- 0.11, respectively; p less than 0.01 for each). In the patients with nonobstructive HC with giant negative T waves, increased apical wall thickness with apical cavity obliteration was characteristic, and the ratio of ventricular septal to apical wall thickness index (0.66 +/- 0.14) was less than that in the patients with obstructive HC or in those with concentric LV hypertrophy (1.46 +/- 0.38 and 1.04 +/- 0.09, respectively; p less than 0.001 for each). In contrast, technically satisfactory 2-D sector scanning (83%) demonstrated various configurations of the hypertrophied ventricularseptum, but could not detect apical hypertrophy in 4 of the 10 patients with nonobstructive HC with giant negative T waves whose LV cineangiograms demonstrated apical hypertrophy. Thus, thallium-201 emission-computed tomography is useful in evaluating the characteristics of LV hypertrophy and assists 2-D sector scan, especially in patients with apical hypertrophy in HC.

Glucose metabolism and rate constants in Alzheimer's disease examined with dynamic positron emission tomography scan

ABSTRACT— Glucose metabolic rate constants in patients with Alzheimers disease were analyzed using dynamic positron emission tomography with [18‐F] fluoro‐2‐deoxyglucose (FDG). The cerebral metabolic rate of glucose (CMRG) was calculated using obtained rate constants, as well as the autoradiographic method. The half‐life and distribution volume of FDG between the blood and the brain tissue were also calculated from obtained metabolic rate constants. The most severely affected metabolic step was the phosphorylation of glucose in the parietotemporal regions. The distribution volume of FDG showed no remarkable deviation from normal controls, while the half‐life of FDG was found to be longer in the parietal and temporal regions. The CMRG from rate constants and that from the autoradiographic method showed no remarkable differences.

Measurement of arterial time-activity curve by monitoring continuously drawn arterial blood with an external detector: Errors and corrections

Accurate description of the arterial time-activity curve (ATAC) is of paramount importance in quantitative determination of the regional cerebral blood flow (rCBF) using positron tomography following bolus i.v. injection of O-15 labeled water. Frequent manual sampling from an arterial catheter does not permit sampling in less than 5-sec intervals and runs the risk of missing the arrival time or the peak count. A continuous ATAC monitoring system has been developed. This system consists of a single bismuth germanate detector in a lead shield and a constant-flow aspirator. The arterial blood was drawn continuously from a catheter within the brachial artery into an extended tube and its activity was monitored by the detector as the detector time-activity curve (DTAC). Comparison with the manual sampling from the contralateral brachial artery in the same run revealed that the DTAC differed from the manual sampling not only in delayed arrival but also in the shape of the curve, which was dispersed because of viscosity and the width of the detector field of view. However, deconvolution of DTAC using the experimentally obtained system step response provided an accurate arterial time course, which successfully filled in the gaps of the manual sampling. Moreover, water and blood showed different dispersion in the step response, suggesting that the system function should be determined using blood or a fluid of similar hydrodynamic nature.

Dynamic positron emission tomography with 13N-ammonia in liver tumors

Dynamic positron emission tomography (PET) of the liver tumor was performed with a whole body multi slice PET device and 13N-ammonia. Sixteen patients with hepatocellular carcinoma (HCC) and seven patients with metastatic liver tumor were studied. In 12 of 16 patients with HCC, in which cases rich tumor vessels and dense tumor stain were proven by hepatic angiography, the tumors showed remarkable uptake of 13N-ammonia from the first scan, whereas the radionuclide accumulation was more gradual in the other part of the liver, and high tumor to liver ratio (T/L ratio) (2.62±1.09) was observed in the 1st scan, so that the tumor was clearly visualized by high contrast. However, HCC with poor blood supply from the hepatic artery or central necrosis of the tumor were demonstrated as low T/L ratio. In seven cases with metastatic liver tumor, the accumulation of 13N-ammonia was also lower than the normal liver throughout the scan. The results suggested that hepatic arterial blood flow of the liver tumors can be assessed with dynamic PET, which may provide valuable information for the characterization of tumors as well as for the evaluation of the treatment.

STEREOSPECIFIC TRANSFORMATIONS OF CHIRAL COMPOUNDS USING ANCHIMERIC ASSISTANCE OF ARYLTHIO AND ARYLSELENO GROUP

A new chiral pool method is developed starting from readily available chiral oxiranes, the key step being the substitution reaction through the anchimeric assistance of the arylthio and arylseleno group. The overall transformation is the introduction of nucleopiles into the chiral carbon of the oxiranes with retention of the configuration.

A new subtraction method for obtaining myocardial perfusion images with oxygen-15 water and positron emission tomography

The myocardial positron emission tomograms which are obtained during the perfusion phase following bolus injection of O-15 water (H215O) intravenously require subtraction of the blood pool activity overlaid upon the myocardium. Subtraction has been carried out using the blood pool images obtained in the same position following single inhalation of O-15 labeled carbon monoxide gas (C15O). However, because a difference in activity exists between the left ventricular (LV) cavity and the right ventricular (RV) cavity, simple subtraction of the LV cavity activity using C15O blood pool images induced significant over-subtraction in the right-side heart including the interventricular septum and RV wall. We developed a new method, “two-component subtraction,” in which the C15O blood pool images were decomposed into the right-side and left-side components using the early phase images of the H215O dynamics under the assumption that the whole activity of that phase was distributed in the right-side heart homogeneously. Thus we subtracted the blood pool spillover from RV and LV separately. This method provided myocardial perfusion images of high quality which were well correlated with N-13 ammonia images.

Clinical evaluation of 99mTc-pyrophosphate myocardial emission computed tomography: Comparison with planar imaging

To depict the three-dimensional distribution of 99mTc-pyrophosphate in the heart, emission computed tomography (ECT) was performed, following the conventional planar imaging, in 32 cases with suspected acute myocardial infarction (AMI). There were 23 cases with evidence of AMI, 7 with unstable angina (UA), and 2 with dilated cardiomyopathy (DCM). While the planar images showed discrete cardiac activity in only 11 of the 23 cases (48%) with AMI, the ECT images delineated focal myocardial uptake clearly in 20 of them (87%). On the other hand, the ECT images revealed cardiac blood-pool activity without significant myocardial uptake in all cases with UA and DCM in which the planar images showed diffuse activity. Thus, the ECT imaging of 99mTc-pyrophosphate seems to be a valuable technique for assessing the presence and localization of myocardial necrosis, especially in cases showing diffuse cardiac activity in the planar imaging.