Strategy for the measurement of regional cerebral blood flow using short-lived tracers and emission tomography.

This report describes a strategy for measurement of regional CBF that rigorously accounts for differing tracer partition coefficients and recirculation, and is convenient for use with positron emission tomography. Based on the Kety model, the measured tissue concentration can be expressed in terms of the arterial concentration, the rate constant K, and the blood flow f. The local partition coefficient may be computed as p = f/K. In our approach, maps of K and f are computed from two transverse section reconstructions. The reconstructions are based on weighted sums of projection data measured frequently during the observation period. Theoretical studies of noise propagation in the estimates of K and f were carried out as a function of tomographic count rate, total measurement time, and tracer half-life for varying input functions. These calculations predict that statistical errors in f of between 5 and 10% at a resolution of 1 cm full width at half maximum can be obtained with existing tomographs following i.v. injection. To compare theory and experiment, a series of flow studies were carried out in phantoms using a positron tomograph. These measurements demonstrate close agreement between computed flow and noise estimates and those measured in a controlled situation. This close agreement between theory and experiment as well as the low statistical errors observed suggest that this approach may be a useful tool in clinical investigation.

Positron imaging in ischemic stroke disease using compounds labeled with oxygen 15. Initial results of clinicophysiologic correlations.

Initial results in over 50 patients with stroke suggest that positron images made during continuous inhalation of carbon dioxide labeled with oxygen 15 and molecular oxygen labeled with oxygen 15 provide data on tissue function that may be relevant to acute stroke management. Five cases illustrate the following findings: 15O-activity patterns observed in areas of ischemic injury or infarction are what one would expect if the 15O distributions represented physiologic functions, such as cerebral blood flow and metabolism. Areas of abnormal 15O activity correlate with the clinical or computed tomographic (CT) localization of the deficit. In studies performed acutely, changes in 15O distributions anticipate alterations in CT scans and may be predictive of outcome. Data related to oxygen metabolism correlate better with tissue viability than do those reflecting cerebral blood flow.

Cerebral blood flow and cerebrovascular CO2 reactivity in stroke-age normal controls.

We used the noninvasive 133-xenon inhalation technique to determine cerebral hemodynamics in 55 normal volunteers aged 18 to 88. Values for cerebral blood flow and cerebrovascular CO2 reactivity in fast-clearing tissue (flow gray) and slow-clearing tissue (flow white) were examined as functions of age and in relation to hematocrit, blood pressure, and evidence of extracranial vascular disease. Flow gray declined linearly with age, but no corresponding change was found in flow white or in CO2 reactivity. The data suggest that the progressive fall in flow gray is due to a physiologic aging process.

A model for regional cerebral oxygen distribution during continuous inhalation of 15O2, C15O, and C15O2.

Equilibrium positron brain scans were obtained during continuous inhalation of C15O, C15O2, and 15O2. Inhalation of C15O labels hemoglobin, whereas C15O2 instantaneously labels stable water to H215O. During the continuous inhalation of 15O2, body tissues extract it from the blood in proportion to local metabolism and ultimately convert it to water of metabolism. After 6-8 min of inhalation, a steady-state equilibrium is established in which the inflow of tracer is balanced by its disappearance due to radioactive decay (T1/2 = 2 min) and biologic removal. Mathematical models of the steady-state distributions of C15O, C15O2/H215O, and 15O/H215O are derived. The major results are: a) The steady-state distribution of C15O is insensitive to variations in blood flow and essentially measures blood volume. b) The distribution of H215O during inhalation of C15O2 is dependent, though nonlinearly, on blood flow. c) The distribution of H215O during inhalation of 15O2 depends linearly on the oxygen extraction fraction and nonlinearly on blood flow. d) The dependence on blood flow in the 15O2 steady-state image can be removed by the division, point by point, of the 15O2 image by the C15O2 image.

Techniques for positron scintigraphy of the brain.

Positron scintigrams were obtained in normal subjects and in patients with intracranial tumors and cerebral vascular disease, using a multicrystal positron camera. The radiopharmaceuticals were 68Ga complexed with adenosine triphosphate (68Ga-ATP), 13N-ammonia (13NH3), and 15O2. Six clinical cases are described to illustrate the different cerebral distributions of intravenously administered 68Ga-ATP, 13NH3, and inhaled 15O2. The possible value of these agents in the study of cerebral metabolism and in differential diagnosis of intracranial disease is discussed.

Tension fecal pneumothorax in a postpartum patient.

A 20-year-old woman developed severe shortness of breath 4 h after a cesarean section. Chest roentgenogram showed a pleural effusion and tension pneumothorax; insertion of a chest tube drained liquid stool. At surgery she was found to have a left diaphragmatic defect with herniation, strangulation, and perforation of the transverse colon into the pleural cavity.

Selective arteriography of glomus tympanicum and jugulare tumors: techniques, normal and pathologic arterial anatomy.

Glomus tympanicum and jugulare tumors arise within the middle ear and jugular fossa, respectively, but often extend into the adjacent areas of the skull base and posterior fossa. Multiple branches of the external carotid, internal carotid, and vertebral arteries may contribute to the vascular supply of these lesions. The arteriograms of 15 patients with glomus tumors were correlated with the surgical findings to determine if selective arteriography could define precisely the involvement within the middle ear, jugular fossa, and mastoid. The arteriographic mapping correlated well with the surgical findings in nine of 13 cases that had surgery, but a few important limitations were found. Therefore, a new arteriographic projection, called a transcanalicular view, is proposed that separates the middle ear from the jugular fossa, allowing for better visualization and assessment of the tumor blush.

Experimental in vivo imaging of the cranial perineural lymphatic pathway.

After intraventricular injection of 99mTc antimony sulfide in rabbits (n = 12) and cats (n = 14), radiolabeled colloid was imaged passing into the nasal mucosa and subsequently into the cervical lymph nodes. The cervical lymph nodes accounted for about 12% of the injected dose in rabbits sacrificed at 22-24 hr after injection and about 5% of the injected dose in cats sacrificed at 5-6 hr after injection. In both animals this represented at least one-third of the cerebrospinal fluid colloid clearance. This technique is applicable to in vivo imaging studies of the perineural lymphatic pathway for cerebrospinal fluid absorption in primates and, with modifications, in human subjects.

CT of neonatal herpes encephalitis.

Seven neonates with proven herpes (HSV type 2) encephalitis exhibited a characteristic sequence of findings on cranial computed tomography (CT). The initial CT abnormalities in all infants were fingerlike areas of cortical increased attenuation noted on unenhanced scans obtained 2-30 days after presentation. These usually were accentuated by increased white-matter lucency. Subsequently (more than 30 days after presentation), extensive cerebral destruction, multicystic encephalomalacia, and calcification were seen on follow-up CT scans obtained in five infants.

Reduction of aneurysm clip artifacts on CT angiograms: a technical note.

We describe a head tilt technique for use with CT angiography that reduces beam-hardening artifacts in patients with aneurysm clips. This simple maneuver directs the artifacts away from pertinent anatomy, thus increasing the chances for diagnostic accuracy. No significant changes in the CT angiographic protocol are required, and the maneuver can easily be combined with other artifact-minimizing strategies.

Cholinergic actions of metrizamide.

In a study of the possible mechanisms of the clinical side effects of metrizamide, it was applied to several in vitro model preparations. It was shown that, although high metrizamide concentrations are without noticeable effect on many basic neuronal functions, metrizamide does interfere with cholinergic mechanisms. At concentrations equivalent to, or significantly lower than, those probably achieved during clinical procedures, metrizamide is both an inhibitor of the enzyme acetylcholinesterase and an antagonist of cholinergic transmission. These data suggest the possibility that some of the side effects resulting from clinical procedures employing metrizamide may be explained by its actions on cholinergic synapses.

MR imaging of pituitary adenomas using a prototype resistive magnet: preliminary assessment.

Magnetic resonance (MR) images were obtained with a prototype resistive magnet system in 10 patients, all of whom had been shown to have pituitary tumors by enhanced high-resolution computed tomography (CT). Histologic verification was obtained in eight cases. Inversion-recovery (IR) T1-weighted images revealed the tumor in six of nine cases; saturation-recovery (SR) images with less T1 weighting identified seven of nine tumors; Carr-Purcell-Meiboom-Gill (CPMG) spin-echo T2-weighted images revealed two of four tumors. MR images failed to demonstrate three microadenomas: 5 X 5 X 8 mm, 6 X 6 X 6 mm, and one less than 5 mm in estimated size. In the last pretreatment study, CT had demonstrated a 13 mm maximum diameter adenoma. Repeat CT at the time of MR imaging also showed a partially empty sella and did not resolve the residual adenoma. The larger adenomas were identified readily by MR imaging, which, unlike CT, suggested old tumor hemorrhage in two cases, which was confirmed at surgery and histologic examination. MR and CT images were also compared for relative effectiveness in identifying important perisellar structures.

High-flow angiopathy: cerebral blood vessel changes in experimental chronic arteriovenous fistula.

Profound vascular damage secondary to high-flow extracranial states has been well characterized. However, changes in cerebral vasculature secondary to high-flow states have not been studied. To determine changes related to high-flow states in cerebral vessels, a rabbit model was developed in which torrential flow was created in the vertebrals, carotids, basilar, and vessels of the circle of Willis by means of a carotid-jugular shunt after ligation of the proximal carotid. The clinical, angiographic, and histologic changes noted in the animal model include: abrupt clinical deterioration after a variable interval with some animals developing ptosis, afferent vessel dilatation and the development of prominent anastomotic channels, variable cerebral vessel histopathology--related to duration and relative proximity to the shunt--affecting all three vessel layers, plump, irregular, and clumped endothelium, denuded with adherent platelets, irregular, duplicated, and thinned internal elastic membrane, frayed with invasion of the intima by mesenchymal cells, vacuolization and necrosis of the media muscle, and invasion of adventitia by foreign cells and small blood vessels. The high-flow angiopathy seen in this model may help explain vascular changes associated with high-flow cerebral vascular lesions, as well as other types of vascular damage.

Complementary roles of a noninvasive test battery and DSA in evaluating carotid artery disease.

Initial comparisons of the results of digital subtraction angiography (DSA) and a battery of tests for noninvasive diagnosis of carotid artery disease indicate the two techniques are complementary, rather than competitive. DSA provides important morphologic information at the carotid bifurcation and siphon, but the images are sometimes difficult to interpret with precision. Noninvasive testing gives discrete physiologic information related to hemodynamics, but the findings are less specific for the level of the lesion in the carotid/ophthalmic system. Noninvasive tests may be more useful than DSA for determining if a lesion is hemodynamically significant and whether advanced disease shows evidence of progression on sequential studies. The noninvasive tests are not definitive procedures, but are useful in selecting patients for a contrast study. They are the initial procedure of choice for the patient with asymptomatic bruit. Depending on the clinical situation and quality of the study, DSA can sometimes be a definitive procedure, but in some situations correlative noninvasive test results are necessary to assess whether the patient is a candidate for arteriography and/or surgery.

Estimation of the local statistical noise in emission computed tomography.

A simple modification of the filtered backprojection algorithm is presented for the computation of the local statistical noise in emission computed tomography. The technique is general in that any distribution of radioactivity may be accommodated. When applied to positron emission tomography, it is shown that the effects of photon absorption, random coincidences, radioactive decay, and detector nonuniformity may be included. Calculations have shown the effects of resolution, object size, and photon absorption on the statistical noise of disk-shaped emitters. Comparison of calculation and experiment show close agreement both in magnitude and spatial variation. Measurements of the noise level in tomograms of the brain obtained during continuous inhalation of 150-CO2 demonstrate that estimates of radioactivity concentration with a precision of a few percent are readily attainable.

Computed tomography in extra-dural epidermoid and xanthoma.

Two cases of extradural epidermoid cyst and one case of xanthoma are reported in order to describe the computed tomographic and other radiographic findings. Contrast enhancement of the margin was seen in all of the cases. Absorption values almost as low as those found with cerebrospinal fluid were present in the central region of the lesions.

CSF enhancement for computerized tomography.

Metrizamide cisternography, combined with hypocycloidal tomography, has been performed in 12 patients with possible posterior fossa or parasellar mass lesions with finely detailed images of the basal cisterns resulting. Computed tomography was performed in nine of these patients and produced exceptional images of the cisternal anatomy. The technique of cerebrospinal fluid enhancement may be efficacious in identifying small basal masses not shown with conventional computed tomography, and thus may form an important complement to enhancement by intravenous injection of contrast medium.