Assessment of the CO2 response by means of non diffusible contrast media and angio-CT in patients with cluster headache.

We analyzed the possibility of assessing functional vasomotor changes by means of Arm-Brain Circulation Time (rABCT) and Vascular volume images (Vv) obtained with Angio-CT, in basal condition and following CO2 inhalation, in a sample of 48 patients with cluster headache. CO2 inhalation resulted in the appearance of local changes, which were detected in 28 regions. Analysis by indicator images of Vv-dependent rABCT distribution showed two main patterns: abnormal rABCT mostly evident at the smallest Vv pixels and abnormal rABCT dependent on abnormal Vv distribution. The former pattern was linked to abnormality at the circle of Willis; the latter to abnormal local vasomotor responses. Patients with cluster headache showed both patterns, which prompted us to conclude for the presence of low-degree stenosis in carotid arteries and vasomotor instability in peripheral brain vessels.

Assessment of regional cerebral blood flow images with non-diffusible contrast media and angio-CT. Comparison with Xe-CT.

We derived rCBF (ND-rCBF) images using non-diffusible contrast agent time-density curves obtained by monitoring the first pass with an angio-CT sequence. An appropriate elaboration of the sequence of the images led to the generation of vascular volume (Vv) and regional Arm-Brain circulation time images (rABCT). ND-rCBF was obtained by dividing the Vv image by the rABCT image after having rendered them suitable for such an operation. Regional cerebral vascular volume (rCBF) was assessed by standardizing Vv values with blood contrast concentration and intracranial circulation time (rICT) by subtracting from the rABCT image the inflow mean time, assessed as the lowest rABCT value of the slice. The ND-rCBF images were qualitatively fairly well comparable with synchronous rCBF (D-rCBF) images obtained with the Xe-CT technique. However quantitation of the values by ROI use gave different results, the ND-rCBF image showing considerably higher values. Using indicator images to analyse the rCBF values at different levels of rCBV and rICT, it was shown that there was a significant relation between the two ND-rCBF and D-rCBF values in the 70-80% pixels with higher rABCT and lower rCBF values.

Functional circulation images by angio-CT in the assessment of small deep cerebral infarctions.

We analyzed circulation time (rABCT) and vascular volume density images obtained by angio-computerized tomography (angio-CT) in 63 patients with small deep cerebral infarctions. Abnormalities in the rABCT image were found in 88% of the patients and in the vascular volume image in 48%. Two groups with different clinical pictures were picked out by rABCT changes: one with major-vessel involvement, the other with small-vessel involvement. The perfusional changes found were mainly due to altered vascular canalization rather than to altered vasomotility. The hemodynamic theory could explain the spatial relations between perfusion changes and CT hypodense areas without needing assumptions linking blood flow and metabolism.

Functional circulation and blood-brain permeability images by Angio CT in the assessment of cerebral ischemia.

We performed rapid sequential computerized tomography (CT) scanning following i.v. injection of a bolus of contrast medium, and generated three functional images related, respectively, to intravascular circulation time (rABCT), vascular volume density (Vv) and blood-brain barrier (BBB) unidirectional constant uptake rate (Ki). This was accomplished by calculating the first mathematical moment of the monitored time-density curves about the injection time, and by the multiple time graph analysis described by Patlack and coworkers. A satisfactory resolution was achieved, allowing separate appreciation of changes in rABCT both at large vessels and at tissue small vessels. Combined evaluation of rABCT and Vv images allowed us to draw qualitative conclusions about blood flow and perfusion reserve.

Hemodynamic assessment of vascular malformations by angio CT with generation of functional transit time images.

We performed a CT dynamic study during the first pass of an intravenously injected bolus of a iodinated contrast medium, followed by generation of the regional arm-brain circulation time (rABCT) image, in 11 patients with vascular malformations. All lesions could be detected as changes of rABCT, and the comparison with values of normal arteries and veins allowed the deduction of the hemodynamic conditions of the lesions. Seven cases showed evidence of altered distribution of rABCT in the corresponding brain hemisphere, suggesting a perfusion reserve impairment.

Assessment of 99mTc-HM-PAO parameters with SPECT for improved evaluation of blood flow in cerebral lesions.

A method for investigating the linearity between blood flow and distribution of 99mTc-HM-PAO uptake in patients undergoing single photon emission computed tomography (SPECT) is presented. This method, based on particular elaboration techniques of sequential multiple acquisitions, provides a local index: cumulative transit time (CTT) related to all factors, other than blood flow, affecting 99mTc-HM-PAO uptake. Because a correct qualitative blood flow estimation is based on the uniformity of the above factors, the occurrence of a change of this index indicates a nonlinear relation between blood flow and 99mTc-HM-PAO uptake distributions. It was shown that although linearity between blood flow and 99mTc-HM-PAO uptake may be questionable, a qualitative assessment of blood flow was correct in 100% of ischemic patients. In nonischemic patients this percentage fell to 60%.

Intravenous 99mTc HM-PAO radionuclide angiography as an adjunct to SPECT assessment of cerebral disease.

An application of intravenous radionuclide angiography as an adjunct to SPECT with 99mTc HM-PAO is presented. From the angiographic sequence a two-dimensional parametric image is generated computing, pixel by pixel, the center of gravity (COG) of the local time curves. This index is independent of blood flow and reflects the relation between transmitted and extravasated activity. COG value, compared in two symmetrical regions analyzed for differences in flow by SPECT, may help to state whether a detected SPECT changed uptake is linearly related or not to the corresponding change of blood flow. All 23 ischemic patients taken into consideration had a similar backflux in symmetrical regions with conspicuous changed uptake. In 3 meningiomas and 2 arteriovenous angiomas it was possible to detect the occurrence of a changed backflux in the lesion suggesting a nonlinearity between blood flow and 99mTc HM-PAO uptake.

Single photon emission computed tomography with technetium-99m hexamethyl propylenamino oxime in the clinical assessment of cerebral ischemia. A preliminary evaluation.

94 subjects, 64 with cerebral ischemia of varying severity and outcome, and 30 controls were studied with technetium-99m hexamethyl propylenamino oxime single photon emission computed tomography in order to evaluate the suitability of this technique in the assessment of cerebral ischemia. Decreased uptake corresponding to the side of clinical symptomatology and/or to CT lesion was found in 93% of the patients with complete stroke and in 28% of the patients with transient ischemic attack. This procedure can be a useful tool in the routine examination of ischemic patients, although the mechanism underlying brain uptake is far from being completely understood and the possible quantitative evaluation of regional cerebral blood flow is worthy of further assessment.