Dynamic computed tomographic imaging of regional cerebral blood flow and blood volume. A clinical pilot study

Study of cerebrovascular reactivity to hypercapnia by imaging photoplethysmography to develop a method for intraoperative assessment of the brain functional reserve

Intraoperative assessment of cerebrovascular reactivity is a relevant problem of neurosurgery. To assess the functional reserve of cerebral blood flow, we suggest using imaging photoplethysmography for measuring changes in cortical perfusion caused by CO₂ inhalation. Feasibility of the technique was demonstrated in three groups of anesthetized rats (n=21) with opened and closed cranial windows. Our study for the first time revealed that the hemodynamic response to hypercapnia strongly depends on the cranial state. However, it was shown that regardless of the direction of changes in local and systemic hemodynamics, the ratio of normalized changes in arterial blood pressure and cortical perfusion could be used as a measure of the cerebrovascular functional reserve.

Radiation doses in cerebral perfusion computed tomography: patient and phantom study

The purpose of this study was to investigate radiation doses in cerebral perfusion computed tomography (CT) examination. As a part of routine patient monitoring, data were collected on patients in terms of the skin dose and CT dose index (CTDIvol) and dose-length product (DLP) values. For the estimation of the dose to the lens a phantom study was performed. Dose values for skin and lens were below the threshold for deterministic effects. The results were also compared with already published data. For better comparison, the effective dose was also estimated. The values collected on patients were in the ranges 230-680 mGy for CTDI and 2120-2740 mGy cm for DLP, while the skin dose and estimated effective dose were 340-800 mGy and 4.9-6.3 mSv, respectively. These values measured in the phantom study were similar, while the doses estimated to the lens were 53 and 51 mGy for the right and left lens, respectively.

Correlation between cognitive impairment and cerebral hemodynamic disturbances on perfusion magnetic resonance imaging in European adults with moyamoya disease

Object

Although cognitive impairment has been reported in adults with moyamoya disease (MMD), its relationship with cerebral hemodynamic disturbances has not been investigated. The aims of the present study were to confirm the presence of dysexecutive cognitive syndrome (DCS) in adults with MMD and to explore the relationship of DCS with frontal lobe perfusion as measured by perfusion MR imaging.

Methods

Cerebral blood volume (CBV) ratio and mean transit time delay were measured in frontal and temporoparietal regions using the cerebellum as a reference region in 10 European adults with MMD. In addition, the authors calculated the cerebrovascular reserve (CVR) using the CBV ratio and the acetazolamide challenge. All patients underwent a standardized neuropsychological assessment test battery. The authors defined DCS as an impairment shown on 3 tests or more of executive function.

Results

The authors found DCS in 6 patients. The frontal CVR was lower in patients with DCS than in patients without DCS (mean ± SD: −13.5 ± 13.2% and 20.3 ± 21.3%; p = 0.019, Mann-Whitney U-test). Other parameters of frontal perfusion and temporoparietal CVR were not correlated with DCS.

Conclusions

The authors' findings suggest that DCS is common in European adults with MMD and may be related to frontal perfusion impairment.

Absolute arterial cerebral blood volume quantification using inflow vascular-space-occupancy with dynamic subtraction magnetic resonance imaging

In patients with steno-occlusive disease of the internal carotid artery (ICA), cerebral blood flow may be maintained by autoregulatory increases in arterial cerebral blood volume (aCBV). Therefore, characterizing aCBV may be useful for understanding hemodynamic compensation strategies. A new 'inflow vascular-space-occupancy with dynamic subtraction (iVASO-DS)' MRI approach is presented where aCBV (mL blood/100 mL parenchyma) is quantified without contrast agents using the difference between images with and without inflowing blood water signal. The iVASO-DS contrast mechanism is investigated (3.0 T, spatial resolution=2.4 x 2.4 x 5 mm(3)) in healthy volunteers (n=8; age=29+/-5 years), and patients with mild (n=7; age=72+/-8 years) and severe (n=10; age=73+/-8 years) ICA stenoses. aCBV was quantified in right and left hemispheres in controls, and, alongside industry standard dynamic susceptibility contrast (DSC), contralateral (cont), and ipsilateral (ips) to maximum stenosis in patients. iVASO contrast significantly correlated (R=0.67, P<0.01) with DSC-CBV after accounting for transit time discrepancies. Gray matter aCBV (mL/100 mL) was 1.60+/-0.10 (right) versus 1.61+/-0.20 (left) in controls, 1.59+/-0.38 (cont) and 1.65+/-0.37 (ips) in mild stenosis patients, and 1.72+/-0.18 (cont) and 1.58+/-0.20 (ips) in severe stenosis patients. aCBV was asymmetric (P<0.01) in 41% of patients whereas no asymmetry was found in any control. The potential of iVASO-DS for autoregulation studies is discussed in the context of existing hemodynamic literature.

Acetazolamide as a vasodilatory stimulus in cerebrovascular diseases and in conditions affecting the cerebral vasculature

Pathologic processes affecting the brain vessels may damage cerebral vasodilatory capacity. Early detection of cerebral dysfunction plays an important role in the prevention of cerebrovascular diseases. In recent decades acetazolamide (AZ) has frequently been used for this purpose. In the present work the mechanism of action and the previous studies are reviewed. The authors conclude that AZ tests are useful in cerebrovascular research. Further investigations are recommended to prove how impaired reserve capacity and reactivity influence the stroke risk in patients and whether these tests may indicate therapeutic interventions.

Ultrasonographic assessment of global cerebral blood volume in healthy adults

The authors describe a new ultrasonographic method for analysis of global cerebral blood volume (CBV) and its application under controlled hyperventilation. CBV was determined as the product of global cerebral blood flow volume (CBF) and global cerebral circulation time. CBF was measured by duplex sonography and calculated as the sum of flow volumes in both internal carotid arteries and vertebral arteries. Extracranial Doppler assessed cerebral circulation time by determining the time interval of echo-contrast bolus arrival between internal carotid artery and contralateral internal jugular vein. Forty-four healthy volunteers (mean age 45 +/- 19 years, range 20-79 years) were studied. Mean CBV was 77 +/- 13 mL. CBV did not correlate with age, end-tidal carbon dioxide level, heart rate, or blood pressure. Hypocapnia was induced in 10 subjects by controlled hyperventilation. Mean reduction of end-tidal carbon dioxide values by 9 +/- 1 mm Hg led to a significant increase in cerebral circulation time (6.1 +/- 0.9 to 8.4 +/- 1.1 second, P < 0.0001) and a significant CBF decrease (742 +/- 85 to 526 +/- 77 mL/min, P < 0.0001), whereas CBV remained unchanged (75 +/- 6 to 73 +/- 10 mL).

Comprehensive imaging of ischemic stroke with multisection CT

Computed tomography (CT) is an established tool for the diagnosis of ischemic or hemorrhagic stroke. Nonenhanced CT can help exclude hemorrhage and detect "early signs" of infarction but cannot reliably demonstrate irreversibly damaged brain tissue in the hyperacute stage of ischemic stroke. Further evaluation of patients with ischemic stroke should include differentiation between reversible and irreversible brain damage, which is essential for choosing an appropriate therapy. Perfusion CT provides information about brain perfusion, which permits differentiation of irreversibly damaged brain tissue from reversibly impaired "tissue at risk." CT angiography can help detect stenosis or occlusion of extra- and intracranial arteries. Multisection CT allows the combined use of all three imaging modalities-nonenhanced CT, perfusion CT, and CT angiography-to rapidly obtain comprehensive information regarding the extent of ischemic damage in acute stroke patients. Specific patterns of findings are typically seen in ischemic stroke and can be analyzed more accurately with the combined use of multisection CT and MR imaging. Nevertheless, prospective studies involving a large number of patients will be needed to ascertain the treatment of choice for patients with each of these patterns of findings.

Multimodal ultrasound assessment of cerebral hemodynamics in a patient with a diffuse cerebral angiomatosis

Recent newly developed ultrasound (US) techniques extend our ability to study the cerebral hemodynamics in patients with arteriovenous malformations (AVM) beyond the conventional cerebral blood flow velocity (CBFV) analysis. We present US data of global cerebral blood flow (CBF) and global cerebral circulation time (CCT) in a patient with a unique bihemispherial diffuse cerebral angiomatosis and compare them with 10 age-matched controls. In addition, the estimation of an US-derived global cerebral blood volume (CBV) is proposed. Duplex sonographic CBF analysis revealed 2620 mL/min in the patient and 754 +/- 93 mL/min in controls. Doppler sonographic CCT was 2.9 s and 6.3 +/- 1.5 s and CBV 126 mL and 79 +/- 19 mL, respectively. US allows a simple, minimal invasive bedside analysis of several global hemodynamic parameters that might provide valuable additional information in patients with diffusely altered cerebral hemodynamics.

Radiation-induced regional cerebral blood volume (rCBV) changes in normal brain and low-grade astrocytomas: quantification and time and dose-dependent occurrence

PURPOSE

New tumor-conformal radiation-treatment modalities have been established with the intention to spare normal tissue while maintaining or improving local tumor control. To document radiation-induced changes in normal brain and low-grade astrocytoma we measured regional cerebral blood volumes (rCBV) using a dynamic susceptibility-weighted contrast-enhanced MR technique (DSC-MRI). We attempted to assess pretherapeutic rCBV values and time- and dose-dependent changes following radiotherapy.

METHODS AND MATERIALS

For prospective and longitudinal assessment of rCBV in normal brain and low-grade astrocytoma, 25 patients with histologically proven fibrillary astrocytoma (WHO Grade II) were examined before radiotherapy and during follow-up. Based on CT- and MR-data sets in a stereotactic setup, three-dimensional (3D) treatment planning was done. Radiotherapy was delivered using fractionated stereotactic radiotherapy (FSRT) to mean and median total doses of 60.9 and 60 Gy, respectively (range, 55.8-66 Gy). During MR imaging for treatment planning and follow-up examinations, 55 T2-weighted gradient echo images were acquired before, during, and after intravenous contrast bolus injection. The acquired signal-time curves were converted into concentration-time curves. The area under the tissue concentration-time curve was calculated and normalized to an integrated arterial input function. Thus, absolute rCBV values could be calculated.

RESULTS

Pretherapeutic mean rCBV for normal gray (GM) and white brain matter (WM) were 7.2 +/- 2.7 and 3.6 +/- 1.5 mL/100 g tissue, respectively. Mean rCBV for astrocytoma was 6.5 +/- 3.7 mL/100 g tissue. After radiotherapy, rCBV for GM and WM was significantly reduced (p < 0.01) in high-dose areas (40-100% of total dose). A nonsignificant reduction was measured in low-dose areas (up to 40% of total dose). Reduction of rCBV in astrocytomas to a plateau level of 4.6 +/- 0.4 mL/100 g tissue was measured at 6 months after radiotherapy and remained stable in locally controlled tumors.

CONCLUSION

Monitoring of rCBV changes in normal brain and low-grade astrocytoma was feasible using a DSC-MRI technique. The method was able to document radiation effects in low-grade astrocytoma, even if the majority of tumors showed no change in diagnostic MR-imaging. Radiation induced decrease of rCBV in GM and WM was correlated to total dose delivered to a tissue area, with high doses causing a significant decrease. Minor decline of rCBV in GM and WM outside high-dose areas after stereotactic radiotherapy confirms the efficacy to spare normal brain tissue by the use of modern conformal radiotherapy techniques. Nonetheless, a critical minimal dose initiating rCBV changes is yet unknown.

Cerebral blood volume and blood flow at varying arterial carbon dioxide tension levels in rabbits during propofol anesthesia

There are little data on the effects of propofol on cerebral blood volume (CBV). We studied the effects of changes in PaCO(2) on CBV and cerebral blood flow (CBF) during propofol anesthesia in eight New Zealand white rabbits. We also investigated the effects of propofol over time on CBV and CBF during normocapnia (control group). At normocapnia, the mean (+/- SD) CBV and CBF values were 2.41 +/- 0.68 mL/100 g and 56 +/- 28 mL/100 g/min, respectively,. When PaCO(2) was reduced from 41 to 27 mm Hg, no significant change in either CBV or CBF was observed (P > 0.10). However, increasing PaCO(2) from 41 to 58 mm Hg resulted in a 30% increase in CBV (3.08 +/- 0.86 mL/100 g, P < 0.05) and a 91% increase in CBF (97 +/- 39 mL/100 g/min, P < 0.01). In the control group, there were no significant changes in CBV and CBF (P > 0.10) during 2 h of propofol anesthesia. These results indicate that, during propofol anesthesia, cerebrovascular reactivity of blood flow and blood volume is maintained during hypercapnia but is markedly diminished during hypocapnia.

IMPLICATIONS

During propofol anesthesia in rabbits with normal brains, a reduction in the arterial carbon dioxide level may not always be accompanied by a reduction in brain blood flow and blood volume.

CT assessment of cerebral perfusion: experimental validation and initial clinical experience

PURPOSE

To validate a dynamic single-section computed tomographic (CT) method to measure cerebral blood volume (CBV) and cerebral blood flow (CBF) by using a noncarotid artery as the input and to demonstrate the feasibility of this method in a pilot series of patients.

MATERIALS AND METHODS

Twelve dynamic contrast material-enhanced CT studies were performed in beagles. CBV, CBF, and mean transit time (MTT) values were calculated by using an internal carotid artery (ICA) and a noncarotid artery as the input artery to the brain. Patient studies with use of the radial artery as the input were performed (a) repetitively in two patients after subarachnoid hemorrhage, (b) in a patient with a symptomatic ICA occlusion before and after the intravenous injection of 1 g of acetazolamide, and (c) in a patient with a malignant brain tumor.

RESULTS

Linear regression analyses revealed highly significant correlations (P < .001) between CBV (r, 0.98; slope, 0.96), CBF (r, 0.89; slope, 0.87), and MTT (r, 0.80; slope, 0.76) values calculated with the ICA and the noncarotid inputs. The CT-derived patient data correlated well with ancillary clinical and neuroradiologic findings.

CONCLUSION

Dynamic single-section CT scanning to measure CBV and CBF on the basis of a noncarotid input is a highly accessible and cost-effective blood flow measurement technique.

Quantitative assessment of cerebral hemodynamics using CT: stability, accuracy, and precision studies in dogs

PURPOSE

The limited clinical availability of currently used methods to measure regional cerebral blood volume (CBV) and cerebral blood flow (CBF) represents an important restriction. We undertook this study to evaluate a new dynamic CT method to measure CBV and CBF in normal and ischemic tissue.

METHOD

A total of 21 dynamic CT studies were performed in seven male beagles. The contrast enhancement curves of the carotid arteries and of various brain regions were deconvolved to obtain CBV and CBF. The stability of the deconvolution method employed was assessed by comparing three data sets obtained by analyses of one, two, and four regions of interest (ROIs), all covering the entire brain area. The accuracy of CT-derived CBF was analyzed for normal (n = 5 studies) and ischemic (n = 7 studies) brain tissue using fluorescent microspheres. Repetitive CT studies were performed to evaluate the precision of the CT measurements.

RESULTS

The stability of the deconvolution method was high with variabilities of 2.3% (CBV), 5.9% (CBF), and 8.9% (mean transit time), respectively. The correlation between the CT and the microsphere measurements was good for both normal and ischemia studies (r > 0.78, slope > 0.9). The variability of the CT CBF (30.6%) was higher than that of the CT CBV (12.3%) measurements.

CONCLUSION

Our novel dynamic CT method is stable with respect to the sizes of ROIs used, allowing for accurate measurements of CBV and CBF in both normal and ischemic tissue. Further studies are necessary to evaluate the variability of this method under controlled physiologic conditions.

Cerebral blood volume maps with dynamic contrast-enhanced T1-weighted FLASH imaging: normal values and preliminary clinical results

PURPOSE

In this article we investigate the application of a method that uses the relaxation effect of bolus-like injected Gd-DTPA to quantify regional cerebral blood volume (rCBV). The aim of the study was to determine if the method provides correct rCBV values in healthy subjects as well as to obtain additional diagnostic information for patients with a glioma or stroke.

METHOD

Twenty healthy subjects, 12 patients with brain infarctions, and 18 patients with gliomas were examined. A series of 64 sequential images of one slice was recorded during bolus transit with a FLASH sequence. The measured signal intensity-time curves were converted pixel-wise to concentration-time curves from which the rCBV images were calculated applying the indicator dilution method.

RESULTS

An average value for gray and white matter of 4.4 +/- 1.6 vol% was obtained for the group of healthy subjects. The grading of the tumors could be classified according to the differences of their corresponding rCBV values. Fifty percent of the infarct patients had to be excluded from the analysis in the acute phase due to mispositioning of the slice and data degradation by gross motion artifact. Different rCBV values were found for areas that develop later into gliotic scars or cystic necrosis.

CONCLUSION

The proposed method is easy to apply in clinical routine MR investigations and provides valuable information for noninvasive, preoperative assessment of tumor grading. It can also provide additional criteria for estimating the histological outcome and with it the degree of ischemia in stroke patients.

Clinical cerebrovascular applications of arterial ultrasound volume flow rate estimates

A variety of disorders affect cerebral hemodynamics. Volume flow rate (VFR) estimates now allow accurate quantification of the effect of cerebrovascular lesions on the conduit vessels, with excellent in vivo and in vitro correlation. Four selected cases with VFR data and angiographic correlation are presented to illustrate potential clinical uses of this method. The VFR estimates were obtained with a color M-mode-based velocity imaging technique, which uses time-domain processing (P-700 Color Velocity Imaging System, Philips Ultrasound International, Irvine, CA). In a patient awaiting coronary artery surgery, with unilateral internal carotid artery occlusion and contralateral angiographic stenosis (50-80%, reader variation), the baseline and acetazolamide-challenged common carotid artery VFRs showed excellent conduit function ipsilateral to this stenosis. Thus, the angiographic stenosis did not have significant hemodynamic effects and endarterectomy was avoided. In a patient with an arteriovenous malformation fed by the left vertebral and left external carotid arteries, high in the left cervical region, VFR estimates of two to three times normal predicted the feeding vessels, influenced management, and proved helpful in follow-up. In a patient with subclavian steal syndrome, VFR estimates quantified the steal after brachial hyperemia. Finally, in a patient with delayed vasoconstriction after subarachnoid hemorrhage, very low VFR estimates preceded clinical deterioration. Quantification of hemodynamic changes with VFR estimates was useful for the diagnosis, management, and follow-up of these patients with four types of cerebrovascular disease, and should be applicable in many others.

Age dependency of the regional cerebral blood volume (rCBV) measured with dynamic susceptibility contrast MR imaging (DSC)

The changes of the regional cerebral blood volume (rCBV) with age were studied using dynamic susceptibility contrast MRI (DSC). We examined an unselected, random sample of 71 consecutive patients referred for work-up of suspected intracranial tumors (35 normal examinations, 36 tumors) with a standard 1.5 T clinical MR system. Determination of the rCBV was performed with a T2*-weighted simultaneous dual (SD) FLASH sequence (TR/TE1/TE2/alpha = 32/25/16/10 degrees, 55 images) after bolus injection of Gd-DTPA. Absolute quantification of the rCBV was achieved by normalizing the measured tissue concentration-time curves with the integrated arterial input function (AIF), which was simultaneously measured in the brain feeding arteries. The rCBV (mean +/- SD) was 8.4 +/- 2.9 ml/100 g and 4.2 +/- 1.7 ml/100 g in gray and white matter, respectively, with a decline of about 3% and 6% per decade for white and gray matter, respectively. We conclude that DSC using a SD FLASH sequence allows the simultaneous measurement of the AIF and the tissue concentration-time curve and thus an absolute quantification of the rCBV, which is the basis for interperson comparisons and follow-up studies.

Peak time difference of time-density curve in contrast media transit as an indicator of asymmetric cerebral perfusion

Time-density curve study in contrast media transit has a theoretical possibility to evaluate asymmetric cerebral perfusion. We studied the right-to-left hemispheric difference of peak time in regional time-density curve. Twenty-seven chronic stroke patients underwent either dynamic CT or intravenous digital subtraction angiography (IVDSA), and single photon emission CT (SPECT). We placed symmetric regions of interest as appropriate in each study, and obtained a peak time of each regional time-density curve in IVDSA or dynamic CT, and a laterality index of reconstructed counts in SPECT. Right-to-left difference of peak time significantly correlated to the laterality index both in IVDSA and dynamic CT (r = -0.88, p < 0.001, and r = -0.82, p < 0.001, respectively). Thus, time-density curve study well reflected unilateral reduction of cerebral perfusion. Recent progress in acute thrombolytic intervention for ischemic stroke recommends a quick and efficient evaluation of ischemic status, and time-density curve study may satisfy this requirement.

The effect of acetazolamide on regional cerebral blood oxygenation at rest and under stimulation as assessed by MRI

The sensitivity of gradient echo magnetic resonance imaging (MRI) to changes in cerebral blood oxygenation (CBO) has been introduced for mapping functional brain activation. Here, we report that this approach allows monitoring autoregulation in the human brain under vasodilatory stress. Following the administration of acetazolamide, signal intensities of deoxyhemoglobin-sensitive images increased in cortical and subcortical gray matter and to a lesser extent in white matter. This result reflects a venous hyperoxygenation stemming from an increase in cerebral perfusion with oxygen consumption remaining constant. In addition, pharmacologic induction of vasodilation attenuated activity-related MRI signal changes in the visual cortex under photic stimulation. Although intersubject variability was high, this finding indicates individually persisting autoregulatory responsiveness to functional challenge despite an "exhausted" reserve capacity. It is suggested that recording CBO by MRI will foster our understanding of modulation of vasomotor tone and cerebral perfusion. Furthermore, this technique may prove valuable for assessing the cerebrovascular reserve capacity in patients with carotid artery occlusive disease.