Giovanni Di Chiro

Glucose utilization of cerebral gliomas measured by [18F] fluorodeoxyglucose and positron emission tomography

Positron emission tomography was used to measure local cerebral glucose utilization by the 2-[18F]fluoro-2-deoxy-D-glucose technique in 23 patients with cerebral gliomas. All 10 high-grade (III and IV) astrocytomas demonstrated a region of high activity with a glucose consumption of 7.4 ± 3.5 (SD) mg/100 gm per minute. The 13 low-grade (I and II) gliomas had a glucose metabolic rate of 4.0 ± 1.8 mg/100 gm per minute, with no distinctly visible hot spot. Thus, we found a correlation between rate of glycolysis and malignancy in primary cerebral tumors. Cerebral cortical glucose utilization was often depressed in areas adjacent to or neurally connected to the tumor site, and there was focal irregular delta wave EEG activity in these areas.

Abnormal CT Scans of the Brain in Asymptomatic Children with Acute Lymphocytic Leukemia after Prophylactic Treatment of the Central Nervous System with Radiation and Intrathecal Chemotherapy

Abstract Thirty-two asymptomatic patients with acute lymphocytic leukemia, who had received prophylactic cranial radiation (2400 rads) and either intrathecal methotrexate or cytosine arabinoside were studied by computed tomography of the brain 19 to 67 months after initiation of prophylaxis. Seventeen of 32 (53 per cent) had one or more abnormal findings. Dilatation of the ventricles (eight patients) and widening of the subarachnoid spaces (nine patients) were equally distributed among patients in both intrathecal-chemotherapy groups. Areas of decreased attenuation coefficient (hypodense, abnormally radiolucent regions) (four patients) and intracerebral calcification (one patient) — lesions previously described in methotrexate leukoencephalopathy —were found only in those who had received intrathecal methotrexate. Mild Central-nervous-system dysfunction was detected in seven patients but did not correlate with the presence of tomographic abnormalities. Nevertheless, these tomographic findings may represen...

Theory of Image Reconstruction in Computed Tomography

Mathematical methods are of central importance in the new technologies of radiographic and radioisotopic image reconstruction. The most important procedures are classified as Back-projection, iterative, and analytical (Two-dimensional Fourier, Filtered Back-projection). Back-projection played an important historical role but is no longer used because of sizable artifacts. Analytical methods excel in speed and accuracy when a large number of projections are available and are extensively used in x-ray imaging. Iterative reconstruction is more attractive when the number of views is limited, if noise is significant, and if additional factors, e.g., gamma-ray attenuation, are present. For these reasons, iterative methods are widely used in radioisotope imaging.

Statistical limitations in x‐ray reconstructive tomography

Statistical fluctuations, or noise, in reconstructed tomograms are analyzed as a function of x-ray energy. The result is essentially constant for energies above 50 keV, assuming constant dose and spatial resolution, and is in close agreement with the actual performance of the EMI-Scanner (water-bag model). The noise is inversely proportional to the square of cell dimensions. For scanners without a water bag, the theoretical noise is approximately 30% less.

Magnetic resonance imaging of stationary blood: A review

The magnetic resonance imaging appearance of blood, as with other body tissues, is affected strongly by magnetic relaxation rates of the water protons. For blood containing only oxyhemoglobin, as for most tissues, the relaxation times are determined by diamagnetic effects related primarily to protein content. However blood containing either deoxyhemoglobin or methemoglobin exhibits additional paramagnetic relaxation effects, which have important consequences for magnetic resonance imaging of hematomas. First, the field inhomogeneity created by the concentration of paramagnetism in the red blood cells lowers the effective T2. This effect depends on field strength, and so is more striking at high fields, and is greater if gradient echoes are used. In fact, the observation of a difference in T2 with the two different echo methods provides an unequivocal indication of field inhomogeneity such as is produced by erythrocytes. A second paramagnetic relaxation effect is the direct interaction of protons with the electron spin of methemoglobin, which markedly lowers both T1 and T2. This effect is important in the imaging of hematomas that are at least several days old, after significant conversion of hemoglobin to the met form has taken place.

Spinal descent of cerebrospinal fluid in man

The descent of radiopharmaceuticals injected within the right lateral ventricle toward and into the spinal subarachnoidal spaces has been followed by scintiphotographic techniques and by computerized flow analysis in a group of “normal” patients. A substantial and rapid downward progression of the albumin-tagged tracer has been observed. This progression is faster than the subarachnoidal ascent toward the convexity of the brain.

Brain parenchyma apparent diffusion coefficient alterations associated with experimental complex partial status epilepticus

The objective of this study was to evaluate whether water apparent diffusion coefficient (ADC) measurements provide more specific information than T2-weighted MRI about the evolution of brain parenchyma lesions secondary to prolonged complex partial seizures. We measured the ADC in the brain of rats exhibiting prolonged complex partial seizures induced by intraperitoneal injection of kainic acid (KA). The animals were imaged with diffusion and T2-weighted MRI at 2 T from 3 h up to 9 days after KA injection. In the piriform cortex and amygdala, the T2-weighted MRI signal intensity appeared to be uniformly increased from 24 to 72 h after KA injection, and returned to normal by 9 days. In the same regions between 24 and 72 h, the ADC first decreased and then increased. The ADC changes were consistent with the known histopathologic alterations. In this complex partial seizure model, the ADC measurement provides more specific information than T2-weighted MRI about the histopathologic evolution of the lesions. This supports the proposal that diffusion MRI may be valuable for the evaluation of the neuropathologic sequelae in patients with multiple or prolonged seizures.

Tissue Signatures with Dual-Energy Computed Tomography

By providing information on two parameters, dual-energy computed tomography can offer clinically useful tissue signatures for metallic deposits (Ca) or injected iodine, as well as for different normal and abnormal types of brain parenchymal tissues and CSF. Cerebral CT was performed on 36 patients and tissue differences analyzed using Hounsfield notation.

High Temporal Resolution Diffusion MRI of Global Cerebral Ischemia and Reperfusion

Although brain ischemia has been extensively studied using diffusion-weighted magnetic resonance imaging, most studies performed so far have not had adequate time resolution to follow the temporal changes in the water apparent diffusion coefficient (ADC) in hyperacute ischemia. Using diffusion echo planar imaging, we obtained ADC maps (calculated from measurements made with 8 b-values) with a time resolution of 43 s in a feline model of global brain ischemia and reperfusion. Different protocols were performed: 10-min hypoperfusion, 10- and 22-min ischemia followed by reperfusion, and cardiac arrest. ADC values were obtained from white matter of the internal capsule and from the thalamus. Cortical gray matter measurements were not deemed reliable due to the close proximity of CSF in the cortical sulci. Following occlusion, the ADC declined in the thalamus to <2 SD of its normal baseline value within 1.5–2.5 min. This decay was exponential with a time constant (τ ± SD) of 6.0 ± 2.6 min; no further decrease in the ADC was observed 10 min following ischemia. Following reperfusion, in animals that showed ADC recovery, the ADC began increasing immediately, returning to its preischemic value in ∼15 min. No significant ADC changes were observed during hypoperfusion. Following cardiac arrest, the decay of ADC was more rapid in the thalamus (τ = 2.6 ± 0.6 min) than in white matter (τ = 6.6 ± 1.8 min). We observed that the ADC at 40 min after cardiac arrest was similar to the ADC at 10 min after ischemia. Given that all animals subjected to 10-min ischemic episodes showed ADC recovery with reperfusion, doubt is cast on whether it is possible to define a threshold value of the ADC below which brain tissue is irreversibly damaged. Finally, despite variability in the time constants of the ADC decay induced by ischemia, the ADC values at 10 min were very similar in all the animals. This suggests that when blood flow is diminished sufficiently to induce an ADC reduction, differences in perfusion affect the rapidity of the decrease but not the final asymptotic value reached.

Computed tomography of spinal cord after lumbar intrathecal introduction of metrizamide (computer-assisted myelography).

Computed tomography (CT) of the thoracic and cervical spine was carried out after lumbar intrathecal introduction of a water-soluble radiographic contrast medium (metrizamide). By choice, no head-down position of the patient was used to facilitate craniad movement of the contrast medium; rather, advantage was taken of the normal CSF flow. This technique, referred to as computer-assisted myelography (CAM), permits the demonstration of the metrizamide-containing subarachnoidal spaces surrounding the thoracic and cervical cord. Some examples of the diagnostic possibilities of the method are discussed.