A new method to estimate rCBF using IMP and SPECT without any blood sampling.

We developed and evaluated a method to measure rCBF without any blood sampling by using iodine- 123 IMP and SPECT. An integral of arterial input function, the integral taken from the value 0 to T of the variable Ca(t)dt, can be expressed as TC(T)/CO, where TC(T) is radioactivity delivered to the body in T minutes and CO is cardiac output. If T is acceptably small, rCBF can be determined by means of a microsphere model analysis with IMP as Cb(T)/(TC(T)/CO), where Cb(T) is cerebral radioactivity at T minutes. We derived TC(T) and CO from a chest dynamic scan. The method was applied to 45 patients who underwent rCBF studies (58 studies) with arterial blood sampling (ABS). Data from the chest scan were analyzed in comparison with ABS data in the first 28 studies, and equations for correction yielding an accurate TC(T)/CO were derived. The validity of the proposed method was evaluated in the subsequent 30 studies. The method yielded rCBF (rCBF-test) which agreed well with rCBF obtained by a two-compartment model analysis of dynamic SPECT and ABS data (rCBF-ref) with the mean and SD of differences between rCBF-test and rCBF-ref being 1.0 and 2.7 ml/100 g/min, respectively. In eleven subjects who underwent more than two studies, a percentage change in rCBF-test between the studies also closely approximated that of rCBF-ref (y = 1.11 x + 2.63, r = 0.92). The method can be used with acceptable reliability to measure rCBF without any blood sampling.

Potential usefulness of 18F-2-fluoro-deoxy-D-glucose positron emission tomography in cervical compressive myelopathy.

STUDY DESIGN: This case study describes the usefulness of high-resolution 18F-2-fluoro-deoxy-D-glucose (18FDG)-positron emission tomography (PET) for metabolic neuroimaging of the cervical spinal cord in patients with compressive myelopathy. OBJECTIVE: To examine whether 18FDG-PET imaging could visualize deterioration of cervical spinal cord function associated with a variable degree of compression and to determine its potential usefulness during assessment of myelopathy. SUMMARY OF BACKGROUND DATA: A few studies have described the use of 18FDG-PET imaging in cervical cord diseases, but visualization of the cervical spinal cord before and after surgical decompression for compressive myelopathy has not been reported. The potential usefulness of 18FDG-PET imaging for assessment of the function of compressed cervical cord has not been discussed previously. METHODS: An 18FDG-PET scan was performed before and after surgery in seven patients with cervical compressive myelopathy. The correlation between the metabolic rate of glucose of the cervical spinal cord and neurologic scores was evaluated. The metabolic rate of glucose in different vertebral levels was also measured. RESULTS: Preoperative metabolic rate of glucose was high in two patients but low in the other five. At the time of the second postoperative examination, metabolic rate of glucose was higher in six of the seven patients, and the increase was associated with neurologic improvement. Use of 18FDG was not related to changes in signal intensities on T2-weighted magnetic resonance images. The metabolic rate of glucose decreased at the affected vertebral level in four patients, increased in two, and did not change in one, relative to the unaffected levels. CONCLUSIONS: High-resolution 18FDG-PET neuroimaging may provide clinically useful qualitative and quantitative estimation of impaired metabolic activity of the compromised cervical spinal cord in compressive myelopathy. 18FDG-PET images may also offer additional information related to neuronal dysfunction induced by mechanical compression.

Influence of speech-coding strategy on cortical activity in cochlear implant users: a positron emission tomographic study.

The effects of a speech-coding strategy of cochlear implant (CI) on cortical activity were evaluated using positron emission tomography. The CIs used in the present study were those of a 22-channel system using the Multipeak speech-coding strategy (MPEAK) and the spectral peak strategy (SPEAK). On comparing the 2 groups, it was found that the speech-tracking performance was significantly higher in the SPEAK group than in the MPEAK group. Regional cerebral blood flow (rCBF) was measured during the silent resting, noise stimulus and speech stimulus periods. The increase in rCBF was localized mainly in the primary auditory area during the noise stimulus period. The increase in rCBF in the auditory association area during the speech stimulus period was stronger in the SPEAK group than in the MPEAK group. This finding suggests that the SPEAK strategy activates more speech processing neuronal networks in the auditory association area than the MPEAK strategy.

Visualization of the cervical spinal cord with FDG and high-resolution PET.

PURPOSE: Our aim was to evaluate the visibility of the cervical spinal cord with [18F]2-fluoro-2-deoxyglucose (FDG) and a high-resolution PET scanner and to quantify the glucose utilization by the cervical cord. METHOD: Twenty-one normal subjects and three cervical myelopathy patients were studied. The visibility of the cervical spinal cord in sagittal and coronal sections was evaluated. The metabolic rate of glucose (MRGlu) and standardized uptake value (SUV) of FDG in the cord were calculated. RESULTS: The entire cervical spinal cord was clearly visualized in 57% of the subjects: the upper cord in 81%, the middle cord in 73%, and the lower cord in 57%. The MRGlu of the normal cord was 1.93 +/- 0.37 mg/100 g/min. SUV was constant across all the vertebral levels and negatively correlated with subject age. In the myelopathy patients, the SUV of the entire cervical cord was lower than in the age-matched normal subjects. CONCLUSION: These preliminary results indicate that the cervical spinal cord can be visualized as a normal structure in routine head and neck PET imaging and that FDG-PET may provide quantitative information about spinal cord disorders.

Cortical processing mechanism for vocalization with auditory verbal feedback.

To investigate the relationship between motor and sensory speech center, cortical activity was examined using PET while normal subjects perceived their own voice which sounded different to the articulated one. The results showed significant activation in the superior temporal gyri with absence of activity in the supplementary motor area (SMA). In a previous study we found significant activation in SMA with no activity in the superior temporal gyrus when normal subjects simply vocalized. Thus, two different cortical pathways for vocalization were delineated: programmed pathway in SMA, and pathway with auditory verbal feedback. The former is thought to be the mature system in the adult, and the latter may be related to speech acquisition.

The role of the temporal coding system in the auditory cortex on speech recognition.

To elucidate the temporal coding system for speech recognition, we synthesized stimulation sounds which do not contain formant information but do contain temporal information by transforming original sound wave to click sequences. Using this stimulation sound, we performed a recognition test and used PET to examine the cortical activities in normal subjects listening to this sound. The results of the recognition test showed a good perception of the sounds made from sequential speech. The PET study demonstrated significant activation of the superior temporal gyri while listening to the stimulation speech sounds. Our results imply that these stimulation sounds were processed semantically in the auditory cortices. The temporal processing system is thought to make an important contribution to speech recognition.

Cortical speech processing mechanisms while vocalizing visually presented languages.

To elucidate cortical processing during vocalization, we used positron emission tomography to measure regional cerebral blood flow during vocalization in six Japanese subjects. During reading Japanese sentences used daily or short syllables aloud, the visual cortices, the left Heschl's gyrus, Broca's area, the primary motor area of the articulatory organs, the supplementary motor area and the cerebellum were significantly activated, compared with resting conditions. The superior temporal gyri were rarely activated. Significant activation of the cerebellum was observed by comparing cortical activity during reading sentences used daily with that during reading meaningless short syllables. These results suggest that vocalization of familiar materials is taken over by the cerebellum, rather than cortical speech areas, and without engagement of the superior temporal gyri.