The Mark IV system for radionuclide computed tomography of the brain

Local cerebral blood volume in head-injured patients. Determination by emission computed tomography of 99mTc-labeled red cells

Local cerebral blood volume (CBV) was mapped in 10 normal subjects and in 30 patients after head injury. In normal subjects, the mean CBV was 4.34 ml/100 gm. The coefficient of variation was 12% for the group mean, and 3% for values obtained in duplicate studies of individuals. Patients with head injuries were divided into three groups according to the stage of their illness: acute illness, early recovery, and later recovery. Averages of mean CBV were within one standard deviation of normal. In contrast, consistent changes were found in serial studies of the mean CBV in the same patient. Compared to recovery values, levels of mean CBV measured soon after injury were reduced, largely at the expense of the gray-matter compartment. In five adults with predominantly unilateral lesions, there was an average early reduction in mean CBV and cerebral blood flow of 15% and 36%, respectively. In three children with diffuse brain swelling, there was an average early mean CBV reduction of 12%; a single child had early increased mean CBV at a time when intracranial pressure was high. Greater changes were seen in local CBV on individual sections. There were mixed zones of hypervolemia and hypovolemia in regions of infarction and intracerebral hematoma. Subdural hematomas had consistent medial margins of increased local CBV, representing dilated blood vessels of the underlying cortex. The presence and displacement of this hypervolemic zone were sensitive indicators of persistent subdural collection and mass effect, even when the collection was lucent to x-ray computed tomography.

Whole-body single-photon emission computed tomography using dual, large-field-of-view scintillation cameras

A whole-body single-photon emission computed tomography system (SPECT) consisting of two large-field-of-view scintillation cameras mounted on a rotatable gantry, a minicomputer and a display station has been designed, constructed and evaluated. In its usual mode of operation, eleven contiguous transverse sections, each 12.5 or 25 mm thick, are reconstructed from projection data acquired during a single, continuous 360 degree rotation lasting from 2 to 22 min. A generalised filtered and weighted backprojection algorithm is used to reconstruct data obtained with conventional parallel-hole collimators in the case of body scanning, or with specially designed fan beam collimators in the case of centrally positioned organs. A simple, yet effective, correction is used to compensate for the effects of gamma ray attenuation within the patient. In addition to providing transverse section images, the system is capable of simultaneous acquisition of opposed conventional scintigrams, the reconstruction of longitudinal section images, and the acquisition of gated cardiac transverse sections. Resolutions in the reconstructed images are typically 15 mm for body scans and 11 mm for brain scans, with only slight variations in sensitivity and resolution within the image. Phantoms and clinical data demonstrate that the SPECT system generates high quality section images while maintaining most of the flexibility of normal scintillation cameras, with the added advantage of dual heads.

Application of ART to time-coded emission tomography

Devices for single-photon emission tomography currently take projections either in a plane over a full angular range (0--360 degrees) or in a volume with a limited angular range. The planar, pseudo-random, time-coded aperture, in conjunction with an Anger camera, is a device of the limited angular range type. It employs multiple pinholes whose transmission varies as a function of time. Previously, image reconstruction was accomplished by simple back-projection of coefficients obtained by time-correlating pinhole transmission with detector-element count rate, resulting in a low-contrast image. Using the Algebraic Reconstruction Technique (ART) a method is introduced for division of the correlation coefficients into subsets allowing the three-dimensional reconstruction to be accomplished on a minicomputer. Results from simulations and experimental phantom data show that ART improves depth resolution compared to back-projection, that under-relaxation produces better images in the case of noisy data, and that the division of the correlation coefficients into subsets has no effect on quality. The images depict the expected resolution degradation in the direction normal to the detector plane due to the limited angular range of projections but yield quantitative results whose relative values are good, even though attenuation is neglected.

Local cerebral blood volume response to carbon dioxide in man

We used an emission tomographic brain scanner to investigate the relationship between local cerebral blood volume (LCBV) and arterial blood carbon dioxide tension (PaCO2) in normal awake man. Measurements were made separately in three dimensions in various regions of grey and white matter, and the resting LCBV as well as the difference in sensitivity among these regions were compared. Over the range of PaCO2 studied (20-42 torr), the response of both the grey matter and the white matter to carbon dioxide was linear. The LCBV sensitivity of the grey matter to changes in PaCO2 was 0.053 ml/100 g per torr PaCO2 and in the white matter this sensitivity was 0.046 ml/100 g per torr PaCO2. These sensitivities were found not to be significantly different, yielding a slope of 0.049 ml/100 g per torr PaCO2 for the LCBV-PaCO2 curve for the entire brain. This is in excellent agreement with the other data for the whole brain. The resting cerebral blood volume of the grey matter at a PaCO2 of 34.4 torr, which was the average resting arterial carbon dioxide tension of the subjects, was 5.0 ml/100 g and was significantly higher than for white matter, which was 3.6 ml/100 g. At the local level, the cerebral blood volume of the frontal cortex is significantly less than that of the thalamus, whereas the frontoparietal cortex in the region of the sylvian fissure has a local cerebral blood volume significantly greater than that of the thalamus.

Radionuclide brain imaging--its role and relation to CT scanning

Separate CNS disease entities are discussed with either the complementary or exclusive indications for radionuclide brain imaging and computerized cranial tomography. Either modality alone has a potential overall precision somewhat in excess of 90% in the localization of cerebral lesions with the effectiveness of each modality differing according to the histology and anatomic location of the lesion. Most investigators agree that the combined application of the two procedures is far superior to their separate use. Routine dynamic isotope studies are essential and in addition, new radiopharmaceuticals and technological advances may improve the radionuclide evaluation of CNS disease. Areas discussed include: primary and secondary CNS neoplasms; acute cerebrovascular accidents; arteriovenous malformations; traumatic cerebrovascular disease; hydrocephalus and dementia; and intracranial inflammatory processes.