Dynamic computed tomography study of the brain

Use of coronary artery calcium and coronary tomography angiography in the evaluation of ischemic heart disease

Over the years, significant technological advances have been made in the field of cardiac CT imaging which has led to the widespread use of the modality in the evaluation of ischemic and structural heart disease. The advent of newer scanning techniques has led to a reduction in scanning time as well as a reduction in the radiation and contrast media dose required - making these scans both convenient and safer to perform. Research has shown that coronary CT angiography has a high negative predictive value in the evaluation of patients with coronary artery disease. There is more recent evidence that coronary CTA has a positive impact on clinical outcomes as well. In this review article, we discuss the clinical applications of coronary CTA in the evaluation of patients with stable ischemic heart disease, the most recent studies evaluating the efficacy and limitations of the modality, the role of coronary calcium in cardiovascular risk prediction in asymptomatic patients and the future applications of the modality.

Ghost infarct core following endovascular reperfusion: A risk for computed tomography perfusion misguided selection in stroke

BACKGROUND

Computed tomography perfusion (CTP) has been increasingly used for patient selection in mechanical thrombectomy for stroke. However, previous studies suggested that CTP might overestimate the infarct size. The term ghost infarct core (GIC) has been used to describe an overestimation of the final infarct volumes by pre-treatment CTP of >10 ml.

AIM

We sought to study the frequency and predictors of GIC.

METHODS

A prospectively collected mechanical thrombectomy database at a comprehensive stroke center between September 2010 and August 2020 was reviewed. Patients were included if they had a successful reperfusion (mTICI2b-3), a pre-procedure CTP, and final infarct volume measured on follow-up magnetic resonance imaging. Uni- and multivariable analyses were performed to identify predictors of GIC.

RESULTS

Among 923 eligible patients (median [IQR] age, 64 [55-75] years; NIHSS, 16 [11-21]; onset to reperfusion time, 436.5 [286-744.5] min), GIC was identified in 77 (8.3%) of the overall patients and in 14% (47/335) of those reperfused within 6 h of symptom onset. The median overestimation volume was 23.2 [16.4-38.3] mL. GIC was associated with higher NIHSS score, larger areas of infarct core and tissue at risk on CTP, unfavorable collateral scores, and shorter times from onset to image acquisition and to reperfusion as compared to non-GIC. Patients with GIC had smaller median final infarct volumes (10.7 vs. 27.1 ml, p < 0.001), higher chances of functional independence (76.2% vs. 55.5%, adjusted odds ratio (aOR) 3.829, 95% CI [1.505-9.737], p = 0.005), lower disability (one-point-mRS improvement, aOR 1.761, 95% CI [1.044-2.981], p = 0.03), and lower mortality (6.3% vs. 15%, aOR 0.119, 95% CI [0.014-0.984], p = 0.048) at 90 days. On multivariable analysis, time from onset to reperfusion ≤6 h (OR 3.184, 95% CI [1.743-5.815], p < 0.001), poor collaterals (OR 2.688, 95% CI [1.466-4.931], p = 0.001), and higher NIHSS score (OR 1.060, 95% CI [1.010-1.113], p = 0.018) were independent predictors of GIC.

CONCLUSION

GIC is a relatively common entity, particularly in patients with poor collateral status, higher baseline NIHSS score, and early presentation, and is associated with more favorable outcomes. Patients should not be excluded from reperfusion therapies on the sole basis of CTP findings, especially in the early window.

Dynamic CTA-Derived Perfusion Maps Predict Final Infarct Volume: The Simple Perfusion Reconstruction Algorithm

BACKGROUND AND PURPOSE

Infarct core volume measurement using CTP (CT perfusion) is a mainstay paradigm for stroke treatment decision-making. Yet, there are several downfalls with cine CTP technology that can be overcome by adopting the simple perfusion reconstruction algorithm (SPIRAL) derived from multiphase CTA. We compare SPIRAL with CTP parameters for the prediction of 24-hour infarction.

MATERIALS AND METHODS

Seventy-two patients had admission NCCT, multiphase CTA, CTP, and 24-hour DWI. All patients had successful/quality reperfusion. Patient-level and cohort-level receiver operator characteristic curves were generated to determine accuracy. A 10-fold cross-validation was performed on the cohort-level data. Infarct core volume was compared for SPIRAL, CTP-time-to-maximum, and final DWI by Bland-Altman analysis.

RESULTS

When we compared the accuracy in patients with early and late reperfusion for cortical GM and WM, there was no significant difference at the patient level (0.83 versus 0.84, respectively), cohort level (0.82 versus 0.81, respectively), or the cross-validation (0.77 versus 0.74, respectively). In the patient-level receiver operating characteristic analysis, the SPIRAL map had a slightly higher, though nonsignificant (P < .05), average receiver operating characteristic area under the curve (cortical GM/WM, r = 0.82; basal ganglia  = 0.79, respectively) than both the CTP-time-to-maximum (cortical GM/WM = 0.82; basal ganglia = 0.78, respectively) and CTP-CBF (cortical GM/WM = 0.74; basal ganglia = 0.78, respectively) parameter maps. The same relationship was observed at the cohort level. The Bland-Altman plot limits of agreement for SPIRAL and time-to-maximum infarct volume were similar compared with 24-hour DWI.

CONCLUSIONS

We have shown that perfusion maps generated from a temporally sampled helical CTA are an accurate surrogate for infarct core.

Intracavernous schwannoma of the abducens nerve: a review of the clinical features, radiology and pathology of an unusual case

We report a case of an intracavernous abducens nerve schwannoma presenting in a 19 year old male of Mediterranean origin. This is only the second report of an abducens nerve schwannoma located entirely within the cavernous sinus. The lesion resulted in a progressive diplopia and focal abducens palsy. The clinical, radiological and pathological features are presented. A literature search has identified only four other abducens nerve schwannomas arising completely or partly within the cavernous sinus. We review these cases and aspects of other ocular cranial nerve schwannomas.

Functional image of dynamic computed tomography in diagnostic and prognostic evaluation of ischemic stroke within the first 6 hours

BACKGROUND AND PURPOSE

It is important to make a diagnosis before a low-density area appears on computed tomography for appropriate management of acute ischemic stroke. We report the diagnostic and prognostic usefulness of functional image of dynamic computed tomography for acute ischemic stroke.

METHODS

Forty-seven patients with ischemic strokes within 6 hours of ictus underwent dynamic computed tomography in which functional images were obtained. These findings were compared with angiographic findings, follow-up computed tomography, and clinical outcome.

RESULTS

The functional images were categorized into three groups: (1) cortical type: abnormalities on time to peak image and/or corrected mean transit time image involving mainly cortical structures (29 cases); (2) noncortical type: abnormalities on either or both images limited to noncortical structures (7 cases); and (3) normal type: no abnormalities on both images (11 cases). Cortical type as a diagnostic test for arterial trunk occlusion had a good sensitivity (100%), specificity (95%), and accuracy (98%). Infarction volume on follow-up computed tomography correlated with extension of prolonged time-to-peak area (r = .80, P < .01) and that of prolonged corrected mean transit time area (r = .81, P < .01). Cortical type was associated with significantly unfavorable outcome (P < .01).

CONCLUSIONS

Functional image of dynamic computed tomography findings predicted arterial trunk occlusion, infarction volume, and clinical outcome. Therefore, this technique would be useful not only for indicating definitive angiography and subsequent therapy but for evaluating the effectiveness of surgical or medical recanalization.

Neurological improvement after cranioplasty. Analysis by dynamic CT scan

The authors studied the changes in neurological signs and cerebral circulation by using dynamic CT scans before and after cranioplasty in six externally decompressed patients. Five of the 6 patients showed some improvements in neurological signs. The results of the dynamic CT scans in 6 cases suggested that increases of bilateral cerebral blood flow may play a role in their neurological improvement.

Dynamic computed tomography and functional imaging in cerebral arterial occlusive disease: analysis in the chronic phase

Dynamic CT was conducted on 10 patients with internal carotid artery (ICA) or middle cerebral artery (MCA) occlusion or stenosis and 14 controls. All the patients were chronic phase and they only presented small infarctions on CT. Those with ICA or MCA occlusions and insufficient collateral circulations showed delayed mean transit time and peak time of the affected side on functional image and in parameter analysis (P less than 0.01) compared with those of controls. A statistically significant positive coefficient of correlation was noted between the degree of the anterior horn dilatation of lateral ventricle and delay in mean transit time of the affected MCA area (r = 0.62, P less than 0.01).

The characteristics of cerebral meningiomas and surrounding tissues on dynamic CT

Dynamic CT was utilized to evaluate 11 patients with histologically benign meningiomas. While it was found that all demonstrated macroscopic neovascularity, subtle differences in the dynamic perfusion curves were identified both between different meningiomas and from region to region within the same tumor. Other than basic anatomic differences, these changes may reflect intratumoral ischemia and hypothetically herald cystic/necrotic alteration within the neoplasm. The dynamic calculations over the surrounding brain showed areas of gross hyper- and hypoperfused cerebral cortex, and hypoperfused white matter in regions of peritumoral edema. These latter findings are of uncertain clinical importance. The dynamic examination also confirmed cases of dural venous sinus invasion and calvarial permeation by tumor. In addition, the dynamic series showed macroscopic neovascularity in one case with a completely negative selective cerebral arteriogram. It is felt that certain cases which have previously been evaluated by static CT may benefit from further study utilizing the dynamic method.

Functional image of dynamic computed tomography for the evaluation of cerebral hemodynamics

We report the usefulness of functional image of dynamic computed tomography as a technique for evaluating cerebral hemodynamics. Although the technique itself has been reported, the advance of computer technology has made it possible to obtain high-resolution functional images within only a few minutes. We conducted 70 examinations on 57 patients with cerebral ischemia and correlated the findings with clinical outcome. Those patients whose abnormalities were detected on all corrected mean transit time, time to peak, and peak value images developed massive cortical infarcts. On the other hand, patients with abnormalities detected only on the corrected mean transit time image had only partial low-density lesions on follow-up computed tomograms. Patients with abnormalities detected only on the time to peak image suffered repeated transient ischemic attacks, but follow-up computed tomograms showed no low-density lesion in most cases. Single-photon emission computed tomography with N-isopropyl-p-(123I)iodoamphetamine performed at the time of functional image of dynamic computed tomography showed a high concordance of the findings in many cases, especially those with hyperacute-stage cerebral ischemia, in which the concordance rate was 90.5% (19 of 21). Comparing images constructed from different parameters, functional image of dynamic computed tomography can delineate other than hemodynamic factors, such as extent of the vascular bed or the degree of collateral circulation. Thus, functional image of dynamic computed tomography is a potentially important and useful technique for the further analysis of cerebral hemodynamics.

Dynamic computed tomography of cerebral parenchymal tuberculomata

The technique of intravenous dynamic cranial computed tomography has been applied to our patient population in Saudi Arabia in which parenchymal tuberculomata make up approximately 10-15% of all cerebral mass lesions. A spectrum of perfusion patterns was observed in tuberculosis progressing from presentation, through treatment, to resolution. These patterns reflect the microscopic vascular evolution of tuberculomata and parallel at least in part the effects of treatment. The method of dynamic scanning further demonstrates its value in improving the specificity of computed tomography in the evaluation of cerebral masses, thereby enhancing patient-beneficial triage.

Dynamic CT of tuberculous meningeal reactions

The technique of intravenous dynamic cranial computed tomography has been applied to the patient population at this location in Saudi Arabia with meningeal tuberculosis. The various manifestations and sequelae including meningitis, arteritis, infarct, and true meningeal tuberculomata all have characteristic if not specific appearances. The dynamic study enhances an otherwise static examination and reveals a great deal about the pathophysiology of tuberculosis involving the cerebral meningeal surfaces.

Cerebral peak time mapping uniformity of the value of peak time

By studying patients with clinically suspected cerebrovascular occlusive disease using dynamic CT technique, we have shown that contrast peak attenuation of the whole normal cerebral tissue was uniformly reached at the same time within a given individual. On the other hand, the delay of peak time was shown to correlate with some vascular occlusive mechanism. The main implications of delayed contrast peak time can be summarized as follows: Reduced regional blood flow due to stenosis or occlusion of main vessel without tissue damage. Delayed contrast arrival time due to occlusion of main vessel, but with sufficient circulation. Tissue organically injured by cerebrovascular occlusion.

The extracranial-intracranial bypass study: how will the outcome affect us?

Extracranial-intracranial bypass is now a commonly performed procedure in centres with a high level of neurosurgical and vascular expertise. Bypass of surgically inaccessible stenoses or occlusions appears to be a logical technique to prevent future stroke but there is much uncertainty about the clinical indications for surgery and even the natural history of the lesions being bypassed. To answer these questions, the International EC/IC Bypass Study was set up in 1977 with relatively broad entry criteria. The data will be analysed in June 1985 and if the results support the use of bypass as a means of preventing subsequent stroke, the procedure should become firmly established. However, if the results are negative, or inconclusive, rather than discard the procedure, subsets of higher risk patients should be sought, in particular using newer methods of assessing cerebral perfusion and metabolism.

Dynamic computed tomography of the brain

Dynamic computed tomography (CT) scanning was performed on five normal subjects, 38 patients with cerebrovascular disorder, and 20 patients with brain tumours. It consisted of performing six rapid sequential scans after intravenous bolus injection of iodinated contrast medium. By gamma variate fit technique, five features (corrected first moment, area, peak, time to peak, and per cent terminal height) were obtained from a time-density curve in a region of interest. We compared these features in one side of the brain with those in the corresponding contralateral side and tried to get information about cerebral perfusion. These results showed that by this technique we are able to detect arterial occlusions or Moya moya diseases non-invasively and know earlier and more clearly the re-establishment of circulation in the occluded arteries and of extravasation of contrast medium in ischaemic regions than by conventional CT scanning. In arteriovenous malformations, serial images of dynamic CT scanning demonstrated the anatomical details of the nidus, and the afferent and efferent vessels. We can also identify an exact extent of tumoral invasion of the brain in patients with malignant brain tumor.

Dynamic studies of brain tumors by the use of digital fluoroscopy

By the use of an expanded X-ray video chain and contrast medium injection, brain tumors can be set off against cerebral tissue. Based on a theoretical model, such weak contrasts behind a strongly absorbing bony structure can be visualized with a nontomographic procedure by massive noise reduction and specialized subtraction technique using an X-ray system optimized to iodine contrasts. During a period of examination, four image series are taken and stored. Dynamic studies concerning redistribution of contrast medium in the intravasal and extravasal spaces of brain tissue and tumor tissue are obtained by the subtraction of stored images. Visualization of the blood flow dynamics has helped to improve internal tumor differentiation and to demarcate the lesion better, especially from a brain edema. As in fluoroscopy, the X-ray tube is operated at a low current so that the skin dose at the radiation entry port amounts to less than 0.4 R for an image series. How practicable this method is in complementing computed tomography is demonstrated by studies of two patients (from a total of 20 patients examined) with a glioblastoma and a third-degree astrocytoma.

Applications of dynamic-CT, or angio-CT in neuroradiology. A disappointing experience

The authors expose their experience in neuroradiological applications of dynamic-CT (D-CT) or angio-CT. The examinations are performed by means of a G.E. 8.800 CT/T. A special software offers automatic analysis of the region of interest. Vascular and tumoral patients are examined trying to evaluate: (a) the blood flow in patients suffering from transient ischaemic attacks and (b) to estimate the possibilities of D-CT in the evaluation of tumoral vascularity and in the identification of characteristic curves for different kinds of tumors.

Vestibular and auditory function in Usher's syndrome

Usher's syndrome is a recessive hereditary disorder in which a congenital hearing loss is combined with nyctalopia, retinal degeneration, and restriction of visual fields. The results of a comprehensive ophthalmic and neurotologic study on 70 patients are reported. Two distinct clinical and presumed genetic types were discernible on the basis of hearing impairment and vestibular sensitivity and, to a lesser extent, deterioration of retinal photoreceptor function. Such a classification has proved valuable in diagnosis, prognosis, and genetic counselling.

Dynamic computed tomographic scans in experimental brain abscess

Dynamic computed tomographic scans were performed in an experimental brain abscess model to establish criteria that could be utilized in abscess staging. The vascular phase of the time-density curves did not differentiate cerebritis and capsule stages. The amount of residual enhancement after the first pass of an intra-arterial contrast bolus differed between major abscess stages, the greater residual enhancement being noted in the capsule stage.

CT response of brain parenchyma to intravenous contrast injections

Pre- and postcontrast scans of the same normal brain tissue layer were compared in 20 patients in order to evaluate postcontrast density response. The original purpose of this investigation was to explain a paradoxical phenomenon of density decrease, which has been regularly observed in our patients. Control phantom measurements revealed that the decrease of density values is a function of the time interval between the analysed and the previous scan. Prolonged interscan interval--due to contrast injection--enables a change in the sensitivity of CT detectors to be registered. It is probable that any study of cerebral blood volume could be unfavourably influenced by this phenomenon. Comparison between the postcontrast brain scan density decrease and density decrease of a phantom showed substantially no difference, so that we estimate the contrast response of the brain parenchyma in toto as insignificant. Further, a comparative analysis between contrast response of the white and gray matter has been made. The gray-white matter difference increased from precontrast 4.56 H to postcontrast 7.82 H. The relatively high difference of 3.26 H between the white and gray matter enhancement compared with negligible enhancement of the brain slice as a whole leads us to the hypothesis, that an absolute decrease of white matter density, as a biological reaction to the injected contrast solution, has to be presumed.

Progress in cerebrovascular disease: local cerebral blood flow by xenon enhanced CT

A noninvasive technique for measuring local cerebral blood flow (LCBF) by xenon enhanced x-ray transmission computed tomography (CT) has been developed an reported quite extensively in recent years. In this method, nonradioactive xenon gas in inhaled and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential computed tomography. Time dependent xenon concentrations within various tissue segments in the brain are used to derive both local partition coefficient (lambda) and LCBF. An assessment of this method reveals that although it provides functional mapping of blood flow with excellent anatomic specificity, there are distinct limitations. The assumptions underlying this methodology are examined and problems associated with various potential applications of this technique are discussed.

In vivo mapping of local cerebral blood flow by xenon-enhanced computed tomography

A noninvasive technique has been developed to measure and display local cerebral blood flow (LCBF) in vivo. In this procedure, nonradioactive xenon gas is inhaled and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential computerized tomography. The time-dependent xenon concentrations in various anatomical units in the brain are used to derive both the local partition coefficient and the LCBF. Functional mapping of blood flow with excellent anatomical specificity has been obtained in the baboon brain. The response of LCBF to stimuli such as changes in carbon dioxide concentrations as well as the variability in LCBF in normal and diseased tissue can be easily demonstrated. This method is applicable to the study of human physiology and pathologic blood flow alterations.

Rapid serial cranial computed tomography for tumor diagnosis

Rapid serial computed tomography (RSCT) provides more information about the cerebral cortical capillary bed and leptomeningeal vessels than conventional enhanced computed tomography (CT). This increased neuroanatomical definition has potential value for separating intra- from extracerebral tumors in selected cases. RSCT offers better visualization of the angioarchitecture of highly vascular tumors than conventional enhanced CT. However, CT scans delayed several minutes after contrast administration are more useful for evaluating the extent of hypovascular tumors. Time-density curves were of limited value for tumor evaluation. However, the peak increase of Hounsfield units did correlate well with the degree of tumor vascularity assessed angiographically.