S. Yoshioka

Functional anatomy of GO/NO-GO discrimination and response selection — a PET study in man

The purpose of this study was to identify the functional fields activated in relation to the NO-GO decision. Nine healthy subjects participated in the study which consisted of two test positron emission tomography (PET) scans (GO/NO-GO task and response selection task) and one control scan. In the response selection task, subjects were asked to flex their thumb of the right hand when a light emitting diode (LED) placed 60 cm from their eyes turned on red and to flex their index finger of the right hand when LED turned on green. In the GO/NO-GO task, subjects were asked to flex their thumb when the LED turned on red, however, they were asked not to move their fingers when LED turned on green. In the control state, they were asked simply to look at the LED without any movement of finger during the course of the scan. The mean regional cerebral blood flow (rCBF) change images for each task minus control and task minus task were calculated and fields of significant rCBF changes were identified. Several fields in the prefrontal cortex of the right hemisphere were specifically activated in relation to the GO/NO-GO task. The results indicate that the prefrontal cortex of the right hemisphere may be a key structure to make a decision not to move.

Regional cerebral blood flow changes of cortical motor areas and prefrontal areas in humans related to ipsilateral and contralateral hand movement.

The regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) in ten normal right-handed volunteers with the purpose of comparing rCBF changes related to movements of the dominant (right) and non-dominant (left) hand. The hand movement task consisted of sequential opposition of the thumb to each finger. The rCBF measured was compared with a rest state. Movements of the dominant hand and the non-dominant hand, increased CBF significantly in the contralateral motor area (MA) and the premotor area (PMA) with small increases in rCBF in the supplementary motor area (SMA). However, movements of the non-dominant hand also elicited significant ipsilateral increases in rCBF in the MA and PMA (6.3% and 5.0%, respectively). Superior part of the prefrontal area (PFA) of the left hemisphere showed significant CBF increases to both left and right hand movement. Our findings indicate that rCBF changes in the motor areas and the PFA of one hemisphere are not related simply to movement of the contralateral hand. Non-dominant hand movement may in addition require activation of ipsilateral motor areas. That is, there appears to be functional asymmetry in the MA and PFA in humans even in this relatively simple and symmetric motor task.

Functional anatomy of taste perception in the human brain studied with positron emission tomography

Regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) in 10 normal volunteers with the purpose of measuring rCBF changes related to taste physiology. Discrimination of 0.18% saline from pure water was associated with significantly increased rCBF values in the thalamus, the insular cortex, the anterior cingulate gyrus, the parahippocampal gyrus, the lingual gyrus, the caudate nucleus, and the temporal gyri. The results indicate that rCBF changes in these structures may reflect oral exposure to salt.

Topographic representation in human intraparietal sulcus of reaching and saccade.

REGIONAL cerebral blood flow was measured by positron emission tomography in seven subjects during reaching with saccade, reaching without saccade, saccade and control tasks. The reaching with saccade task activated two spatially distinct areas in the contralateral intraparietal sulcus (IPS) compared with the control condition. The area located in the anterior part of the IPS was also activated during the reaching without saccade but not during the saccade task. The other area, located in the posterior part of the IPS was, in contrast, active during the saccade but not the reaching without saccade task. The results indicate that the human IPS is functionally heterogeneous, and that functional roles of its anterior and posterior parts include control of reaching movements and eye movements, respectively.

Changes in regional cerebral blood flow during self-paced arm and finger movements. A PET study

The purpose of this study was to identify the functional fields activated in relation to the self-paced proximal and distal arm movements. The regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) and 15O-labelled H2O (H2(15)O) in eight healthy subjects. All subjects performed the following three tasks: (1) repetitive opposition of thumb and index finger of the right hand, (2) repetitive co-contraction of biceps and tricepts brachii muscles of the right arm, and (3) rest. The mean rCBF change images for each task minus control was calculated and fields of significant rCBF changes were identified. Each movement activated different fields in the primary motor area (MI), the dorsal aspect of the premotor area (PMA) and the superior part of the prefrontal area (PFA) of the contralateral hemisphere. In these areas, arm fields were located relatively dorsally to the finger fields. In addition, specific fields in the ventral part of the PMA, the supplementary motor area (SMA), the superior parietal lobule (SPL) of the contralateral hemisphere, and the ipsilateral PFA were consistently activated during both movements. Due to a limited a field of view of the PET scanner in the axial direction, the PET scan could not cover the cerebellum. The results indicate that there may be somatotopical organization not only in the MI but also in the dorsal part of the PMA and the PFA, and that the specific fields in the ventral part of the PMA, the SMA, the SPL, and the PFA may be involved in self-paced movement.

Studies on 18F-labeled pyrimidines. Tumor uptakes of 18F-5-fluorouracil, 18F-5-fluorouridine, and 18F-5-fluorodeoxyuridine in animals

Three 18F-labeled pyrimidines, 18F-5-fluorouridine (18F-5-FUR), 18F-5-fluorouracil (18F-5-FU), and 18F-5-fluorodeoxyuridine (18F-5-FdUR), were examined regarding tissue distribution and tumor uptake in ascitic hepatoma AH109A-bearing rats. The differential absorption ratios of tumors of 18F-5-FUR, 18F-5-FU, and 18F-5-FdUR were 0.75±0.21, 0.92±0.15, and 0.96±0.24 at 30 min, and 0.37±0.09, 0.64±0.34, and 0.60±0.17 at 120 min, respectively. The tumor-to-organ ratios obtained with three radiopharmaceuticals, especially with blood, heart, lung, muscle, and brain were high and these ratios increased with time. The tumor-to-organ ratios obtained with 18F-5-FdUR were always 1.3–4 times higher than 18F-5-FU and 18F-5-FUR. We concluded that 18F-5-FdUR was a suitable radiopharmaceutical for tumor imaging. Positron emission tomography of a rabbit tumor located on the chest with 18F-5-FdUR clearly showed the tumor within 1 h.

Activity in the human primary motor cortex related to arm and finger movements.

With the purpose of mapping representations of the finger and proximal arm in the human primary motor cortex (MI), we measured regional cerebral blood flow (rCBF) in eight right-handed normal volunteers during self-paced finger and proximal arm movements. Each movement activated two different fields in MI, one located deep in the anterior lip of the central sulcus and the other relatively close to the surface of the precentral gyrus. Arm fields were located higher than finger fields. A superficial arm field and a deep finger field partially, overlapped. The results indicate that there are two spatially separate motor representations of the finger and proximal arm in the human MI.

Experimental studies on myocardial glucose metabolism of rats with 18F-2-fluoro-2-deoxy-d-glucose

The myocardial uptake of 18F-FDG was investigated under various conditions, and compared with brain and tumor uptake as a function of blood glucose level. The uptake by the heart of normal feeding rats was rapid and remained essentially unchanged up to 2 h after 18F-FDG injection, approximately 3%–4% dose/g tissue. On the other hand, the myocardial uptake of fasted rats was significantly lower than that of control rats throughout the course of the study, and it was about 0.3%–0.4% dose/g tissue. Myocardial uptake of 18F-FDG was relatively constant at glucose levels under about 120 mg/100 ml and increased steeply at higher blood glucose levels. In contrast, brain uptake decreased linearly with increasing levels of blood glucose, revealing a strong negative correlation between brain uptake of 18F-FDG and blood glucose levels. The tumor uptake pattern remained relatively unchanged, irrespective of blood glucose levels. It was revealed that the glucose demands of brain, heart, and tumor were entirely different. After a glucose load, the myocardial uptake of fasted rats increased only slightly from 0.4% to 0.6% dose/g tissue, in spite of transitional hyperglycemia. In contrast, insulin caused myocardial uptake to increase extraordinarily, although it caused a decrease in blood glucose levels.

Differential Diagnosis of Idiopathic Fibrosis from Malignant Lymphadenopathy with PET and F-18 Fluorodeoxyglucose

Idiopathic fibrosis and malignant lymphoma were studied with positron emission tomgraphy (PET) using 2-deoxy-2-[F-18]fluoro-D-glucose (F-18DG). Cases of retroperitoneal fibrosis and sclerosing peritonitis showed low F-18DG uptake with the mass/muscle radioactivity (M/M) ratio 2.0 and 1.9, respectively. A case of para-aortic adenopathy from malignant lymphoma showed high F-18DG uptake with the M/M ratio 9.4. F-18DG PET study may be useful for the differential diagnosis of idiopathic fibrosis and malignant lymphadenopathy.

2-deoxy-2-[18F]fluoro-d-galactose: A new tracer for the measurement of galactose metabolism in the liver by position emission tomography

We prepared 2-deoxy-2-[18F]fluoro-d-galactose as a potential radiopharmaceutical for liver imaging and for the assessement by position emission tomography of regional metabolic function of the liver. In biodistribution studies of rats, the liver uptake of the compound was very high, almost reaching a plateau (6.33% dose/g) at 30 min and remaining constant until 120 min. This high uptake was reduced by simultaneous administration of d-galactose, but d-glucose had no effect. The compound was much less concentrated in the liver that had been damaged by CCl4 treatment. Positron imaging of a rabbit liver showed a remarkable uptake of the compound with a high liver-to-blood ratio. The high concentration in the liver was also reduced by the administration of d-galactose. These data suggest that the compound was trapped in the liver by a metabolic process and could be used for the measurement by position emission tomography of galactose metabolism in the liver.