Stable xenon versus radiolabeled microsphere cerebral blood flow measurements in baboons.

Regional cerebral blood flow was simultaneously determined using the stable xenon computed tomographic and the radioactive microsphere techniques over a wide range of blood flow rates (less than 10-greater than 300 ml/100 g/min) in 12 baboons under conditions of normocapnia, hypocapnia, and hypercapnia. A total of 31 pairs of determinations were made. After anesthetic and surgical preparation of the baboons, cerebral blood flow was repeatedly determined using the stable xenon technique during saturation with 50% xenon in oxygen. Concurrently, cerebral blood flow was determined before and during xenon administration using 15-microns microspheres. In Group 1 (n = 7), xenon and microsphere determinations were made repeatedly during normocapnia. In Group 2 (n = 5), cerebral blood flow was determined using both techniques in each baboon during hypocapnia (PaCO2 = 20 mm Hg), normocapnia (PaCO2 = 40 mm Hg), and hypercapnia (PaCO2 = 60 mm Hg). Xenon and microsphere values in Group 1 were significantly correlated (r = 0.69, p less than 0.01). In Group 2, values from both techniques also correlated closely across all levels of PaCO2 (r = 0.92, p less than 0.001). No significant differences existed between the slopes or y intercepts of the regression lines for either group and the line of identity. Our data indicate that the stable xenon technique yields cerebral blood flow values that correlate well with values determined using radioactive microspheres across a wide range of cerebral blood flow rates.

MR imaging of model fluid velocity profiles.

A projection MR technique for imaging the velocity profiles of moving fluids has been applied to various steady flow models designed to simulate a variety of flow conditions. From such profiles can be readily deduced peak velocities, volume flow rates, information concerning the degree of flow development, features such as flow separation, and estimates shear stresses at the vessel wall.

Velocity profiles in stenosed tube models using magnetic resonance imaging.

A time-of-flight MRI velocity measurement technique is evaluated against corresponding LDV measurements in a constriction tube model over a range of physiologic flow conditions. Results from this study show that MR displacement images can: 1) be obtained within both laminar and turbulent jets (maximum stenotic Re approximately equal to 4,200), 2) measure mean jet velocities up to 172 cm/s, and, 3) detect low forward and reverse stenosis (0 less than or equal to L/D less than or equal to 2). Regions between the jet termination point and re-establishment of laminar flow (Re greater than or equal to 1500, greater than or equal to 1000, and greater than or equal to 110 downstream of 40, 60, and 80 percent stenosis, respectively) cannot presently be detected by this technique.

An MRI phantom material for quantitative relaxometry.

Most phantom media in current use exhibit T1 relaxation times that are significantly dependent on both temperature and operating frequency. This can introduce undesirable variability into relaxation measurements due to temperature fluctuations, and complicates direct comparison of imagers operating at different magnetic field strengths. Our investigations of a nickel-doped agarose gel system have demonstrated near independence of the proton relaxation rates to a wide range of temperatures and frequencies. We therefore propose the adoption of Ni2+ as a relaxation modifier for phantom materials used as relaxometry standards.

Xenon/computed tomography cerebral blood flow measurements. Methods and accuracy.

We performed a series of five baboon experiments to compare cerebral blood flow measured with an improved stable xenon/CT method and the radiolabelled microsphere technique at a PaCO2 of 40 mm Hg. The xenon/CT method was implemented by fitting the arterial xenon uptake with a double exponential function, by measuring the oxygen and carbon dioxide concentrations continuously during each breath and by taking into account the lung-to-brain transit time of xenon. The time of xenon inhalation was extended to 30 minutes to obtain more reliable estimates of CBF in white matter regions. The results indicate an overall correlation coefficient of 0.92 between the two methods and good numeric agreement.

Computed tomography in the prediction of outcome in head injury.

To determine the prognostic significance of computed tomographic (CT) findings in head injury, retrospective analysis was performed in 128 randomly selected severe head-injury patients managed with a standardized protocol. The minimal criterion for entry into this study was that the patients were unable to obey simple commands or utter formed words. Serial CT was performed on admission and 3-5 days, 2 weeks, 3 months, and 1 year after injury. A scale of severity of abnormalities was devised taking into account the size of the traumatic lesions on CT. The CT findings using the proposed scale were correlated with the clinical outcome and analyzed using linear logistic regression. Other characteristics such as midline shift, multiplicity, and corpus callosum and brainstem lesions were not included in the analysis either because they did not affect the prognosis or because too few of these lesions were present for statistical analysis. The correct prediction rate of outcome using the proposed scale for CT findings alone was found to be 69.7%. When CT findings were combined with the Glasgow Coma Scale score this rate was increased to 75.8%.

Regional cerebral blood flow measurements using stable xenon enhanced computed tomography: a theoretical and experimental evaluation.

Several theoretical and practical aspects of regional cerebral blood flow measurements using stable xenon gas and CT are discussed. It is shown that by comparing the enhancement at any time T1 with that at saturation or any other time T2, the need to use arbitrary means to bring the arterial concentration data and the CT enhancement data to the same system of measurement units can be eliminated. If CT is performed continuously during the washin phase, say at intervals of 1 min, least squares analysis of the enhancement data can be used to obtain the best possible estimates for the flow rate constant kappa and the saturation enhancement. However, if only a limited number of scans can be performed, as may be the case in human studies, it is also possible to get a good estimate of kappa from a knowledge of the ratio of the enhancement at any time T1 with that at any other time T2. Combinations of T1 = 2.0 min and T2 = 4.0 min, T1 = 1.0 min and T2 = 6.0 min, or T1 = 2.0 min and T2 = 5.0 min were found to be the most convenient. It is also shown that the end-tidal xenon concentration in the exhaled air can be accurately assessed indirectly by measuring the oxygen, CO2, and water vapor concentrations, thereby eliminating the need for more expensive methods involving the use of a mass spectrometer or a thermal conductivity gas analyzer.

Ventricular enlargement in teenage patients with schizophrenia spectrum disorder.

Recent research has demonstrated statistically significant differences between the ventricular-brain ratios (VBRs) of schizophrenic patients and control subjects. In this study the VBRs of teenage schizophrenic/schizophreniform patients (N = 15) and borderline patients (N = 8) were measured and compared with those of controls of similar ages (N = 18). The schizophrenic group had significantly larger ventricles than the other two groups (p less than .0001). These findings support the hypothesis of previous investigators that ventricular enlargement is present early in the course of schizophrenia.

Computed tomography in the evaluation of incidence and significance of post-traumatic hydrocephalus.

Two hundred consecutive patients with severe head injury underwent sequential computed tomography (CT) on admission, after 4, 14, and 90 days, and after one year. Ventricular enlargement was evaluated in the surviving patients, based upon serial CT examinations. Significant ventricular enlargement was further evaluated with radionuclide cisternography. A significant correlation was shown between clinical outcome and presence or absence of ventricular enlargement. Radionuclide cisternography provided an additional means of determining those patients whose recovery was impaired by persistent obstruction of cerebrospinal fluid circulation and who would therefore benefit from cerebrospinal fluid shunting.

Significance of CT in head injury: correlation with intracranial pressure.

The authors correlated the computed tomographic (CT) findings and intracranial pressure (ICP) in 150 consecutive comatose head injury patients to determine if noninvasive CT can help identify the patients not requiring ICP monitoring. The study reveals that a majority of patients (55%) with hemorrhagic lesions shown by CT suffer from intracranial hypertension and require ICP monitoring for proper management. Of the patients with normal initial CT, 98% had normal ICP during the first 24 hr. Of the patients with normal CT, 15% developed intracranial hypertension later, irrespective of the initial Glasgow coma scale score or age. More than half of the patients who developed intracranial hypertension subsequently had normal ICP through the first 48 hr. The study indicates that ICP monitoring need not routinely be performed on admission on severe head injury patients with a normal CT. However, repeat CT at 24--48 hr before ICP monitoring in patients with initially normal CT may be valuable, particularly if their clinical status deteriorates.

Craniopharyngioma: Unusual computed tomographic presentation.

Craniopharyngioma usually presents on a computed tomographic (CT) scan as a hypodense or isodense lesion, with calcification, in the suprasellar region. A case with atypical CT findings of a huge, homogeneous, high density, apparently solid, lobulated suprasellar mass is presented. An explanation for the appearance of the tumor is discussed based upon clinical analysis of the tumor contents.

Cervical spinal subdural hematoma.

We report a case of intraspinal subdural hematoma following trauma - a rare entity - with a review of the literature. The location of the hematoma in the cervical spine as described in this report is even more uncommon and was reported only once before. The pathophysiology of this entity is discussed, and the myelographic features are emphasized to facilitate the preoperative diagnosis.

Improved confidence of outcome prediction in severe head injury. A comparative analysis of the clinical examination, multimodality evoked potentials, CT scanning, and intracranial pressure.

An analysis of clinical signs, singly or in combination, multimodality evoked potentials (MEP's), computerized tomography scans, and intracranial pressure (ICP) data was undertaken prospectively in 133 severely head-injured patients to ascertain the accuracy, reliability, and relative value of these indicants individually, or in various combinations, in predicting one of two categories of outcome. Erroneous predictions, either falsely optimistic (FO) or falsely pessimistic (FP), were analyzed to gain pathophysiological insights into the disease process. Falsely optimistic predictions occurred because of unpredictable complications, whereas FP predictions were due to intrinsic weakness of the indicants as prognosticators. A combination of clinical data, including age, Glasgow Coma Scale (GCS) score, pupillary response, presence of surgical mass lesions, extraocular motility, and motor posturing predicted outcome with 82% accuracy, 43% with over 90% confidence. Nine percent of predictions were FO and 9% FP. The GCS score alone was accurate in 80% of predictions, but at a lower level of confidence (25% at the over-90% level), with 7% FO and 13% FP. Computerized tomography and ICP data in isolation proved to be poor prognostic indicants. When combined individually with clinical data, however, they increased the number of predictions made with over 90% confidence to 52% and 55%, respectively. Data from MEP's represented the most accurate single prognostic indicant, with 91% correct predictions, 25% at the over-90% confidence level. There were no FP errors associated with this indicant. Supplementation of the clinical examination with MEP data yielded optimal prognostic power, an 89% accuracy rate, with 64% over the 90% confidence level and only 4% FP errors. The clinical examination remains the strongest basis for prognosticating outcome in severe head injury, but additional studies enhance the reliability of such predictions.

Contrast enhancement in the postoperative brain.

Contrast enhancement simulating an abscess or residual tumor has been described in postoperative cranial computed tomography (CT) scans. This study was undertaken to determine the cause of this contrast enhancement by using canine brain as an experimental model. Sequential CT scanning was performed with and without contrast enhancement following partial resection of the right hemisphere, and the CT findings were correlated with the histological changes. Findings indicate that enhancement of the surgical margin is related both temporally and spatially to the neovascularity following surgery. The ring-like enhancement around the surgical margin is seen best at two to four weeks after surgery, and may simulate an abscess. However, edema seen around an abscess in adjacent brain is absent or minimal in the case of postoperative enhancement during this period, and this feature should help differentiate these entities.

Pituitary microadenoma: a radiological-surgical correlative study.

In this study, the authors evaluated the correlation between the radiological changes in the sella (using thin-section, complex motion tomography) and the location of pituitary microadenomas at surgery. A significant discrepancy was noted between the tomographic and surgical location of the tumor in 14 of 55 patients. The authors caution about absolute reliance upon tomography for making the diagnosis of pituitary microadenoma in a given patient.