Cerebral perfusion CT: technique and clinical applications

Utilization of dynamic CT perfusion in the study of intracranial meningiomas and their surrounding tissue

OBJECTIVE

To use CT perfusion (CTP) to assess levels of ischemia in brain areas around intracranial meningiomas.

MATERIALS AND METHODS

Fifteen patients with intracranial meningiomas were analysed preoperatively with CTP study. The cerebral blood flow (CBF), cerebral blood volume (CBV) and time to peak (TTP) were measured in the edema, peritumoral edema and in the normal areas of brain.

RESULTS

The peritumoral edema measured a mean CBF of 17.36 ml/min/100 ml (median=15.8) and the mean CBF value in the whole edema was 93.86 ml/min/100 ml (median=79.9). The mean CBV measured in the peritumoral edema was 2.7 (median=2.3) and the measured mean CBV of edema was 15 (median=13.2). In the region of the peritumoral edema, the mean CBF and CBV were lower than in the edema bed. Normal brain remote from the edema measured less CBF (mean=28.36 ml/min/100 ml, median=29.7) and CBV (mean=4.1, median=3.8) than the edema. Six patients were noted to have CBF of less than 15 ml/min/100 ml in the perilesional edema. The measured mean CBF and CBV in the normal area of brain were higher than in the peritumoral edema, while the TTP was greater in the perilesional edema (mean=11, median=10.4) when compared with areas of normal brain (mean=9.9, median=9.5) with statistically significant p values.

CONCLUSION

The values obtained elucidate the fact that perilesional edematous areas are ischemic. By subset analysis, it may be possible to identify those areas with recoverable tissue from non-recoverable tissue.

Quantitative analysis of CT-perfusion parameters in the evaluation of brain gliomas and metastases

BACKGROUND

The paper reports a quantitative analysis of the perfusion maps of 22 patients, affected by gliomas or by metastasis, with the aim of characterizing the malignant tissue with respect to the normal tissue. The gold standard was obtained by histological exam or nuclear medicine techniques. The perfusion scan provided 11 parametric maps, including Cerebral Blood Volume (CBV), Cerebral Blood Flow (CBF), Average Perfusion (Pmean) and Permeability-surface area product (PS).

METHODS

The perfusion scans were performed after the injection of 40 ml of non-ionic contrast agent, at an injection rate of 8 ml/s, and a 40 s cine scan with 1 s interval was acquired. An expert radiologist outlined the region of interest (ROI) on the unenhanced CT scan, by using a home-made routine. The mean values with their standard deviations inside the outlined ROIs and the contralateral ROIs were calculated on each map. Statistical analyses were used to investigate significant differences between diseased and normal regions. Receiving Operating Characteristic (ROC) curves were also generated.

RESULTS

Tumors are characterized by higher values of all the perfusion parameters, but after the statistical analysis, only the PS, PatRsq (Patlak Rsquare) and Tpeak (Time to Peak) resulted significant. ROC curves, confirmed both PatRsq and PS as equally reliable metrics for discriminating between malignant and normal tissues, with areas under curves (AUCs) of 0.82 and 0.81, respectively.

CONCLUSION

CT perfusion is a useful and non invasive technique for evaluating brain neoplasms. Malignant and normal tissues can be accurately differentiated using perfusion map, with the aim of performing tumor diagnosis and grading, and follow-up analysis.

Hemodynamic effects of recombinant human erythropoietin on the central nervous system after subarachnoid hemorrhage: reduction of microcirculatory impairment and functional deficits in a rabbit model

OBJECT

The authors investigated the hemodynamic effects of recombinant human erythropoietin (rhEPO) after subarachnoid hemorrhage (SAH) in rabbits.

METHODS

The authors used male New Zealand White rabbits in this study divided into the following groups: SAH plus saline (16 rabbits), SAH plus low-dose rhEPO (16 rabbits; 1500 IU/kg on Day 0 and 500 IU/kg on Days 2 and 4), SAH plus high-dose rhEPO (10 rabbits; 1500 IU/kg on Days 0, 2, 4, and 6), and sham (6 rabbits). Computed tomography perfusion studies and CT angiography were performed for 1 hour after SAH on Day 0, and once each on Days 2, 4, 7, 9, and 16 after SAH. Assessments of neurological function and tissue histology were also performed.

RESULTS

The mortality rate was significantly lower after rhEPO treatment (12%) than after saline treatment (44%) (p < 0.05). Neurological outcomes in the low-dose and high-dose rhEPO groups were better than in the saline group after SAH (p < 0.05), and the cerebral blood flow in the high-dose rhEPO group was greater than that in the saline group (p < 0.05). The mean transit time was significantly lower on Days 2 and 4 in the low-dose and high-dose rhEPO groups than in the saline group, but increased significantly on Day 7 in both groups (p < 0.05). The hematocrit increased significantly from baseline values in the high-dose and low-dose rhEPO groups on Days 4 and 7, respectively (p < 0.05).

CONCLUSIONS

Treatment with rhEPO after experimental SAH is associated with improved cerebral blood flow and microcirculatory flow as reflected by lower mean transit times. Improved tissue perfusion correlated with reduced mortality and improved neurological outcomes. Further investigation of the impact of increasing hematocrit on hemodynamic changes is needed.

CT Perfusion Evaluation of Cerebral Haemodynamics before and after Cranioplasty

CT Perfusion imaging is usually applied to assess perfusion abnormalities in acute stroke. This prospective study applied the technique to monitor cerebral haemodynamics before and after cranioplasty. Cranioplasty is the surgical correction of a skull defect using autologous or heterologous material to obtain cosmetic repair, restoration of brain protection and neurological improvement (1). As far as we know the effect of cranioplasty on cerebral haemodynamics flow has been analysed by CT perfusion only in one article (2). We tested the examination as method of monitoring intracranial haemodynamics in a larger number of patients evaluating its reliability and efficacy. We prospectively examined cerebral haemodynamics with Perfusion CT before and after (two weeks, three and six months) cranioplasty in ten patients. The data evaluation of dynamic CT was done by an application software package on a workstation (Leonardo) permitting the use of visual assessment combined with quantitative analysis with ROIs. There was a comparison of CBF, CBV and TTP values between the regions of interest and mirror-image control regions, and in the three different examinations for each patient. After cranioplasty there was clearly an improvement in neurological symptoms and CT perfusion in the majority of cases showed a slight increase in CBF, CBV and decrease of TTP in the cerebral parenchyma close to the cranioplasty, not only on the symptomatic side but also on the opposite side. Even though there was neurological improvement and improved cranial perfusion from the first to the last examinations, our data were not statistically significant. The method is easily reproducible, well tolerated by all patients but has several limitations related to data processing and radiation exposure.

Advanced gastric cancer and perfusion imaging using a multidetector row computed tomography: correlation with prognostic determinants

Objective

To investigate the relationship between the perfusion CT features and the clinicopathologically determined prognostic factors in advanced gastric cancer cases.

Materials and Methods

A perfusion CT was performed on 31 patients with gastric cancer one week before surgery using a 16-channel multi-detector CT (MDCT) instrument. The data were analyzed with commercially available software to calculate tumor blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability surface (PS). The microvessel density (MVD), was evaluated by immunohistochemical staining of the surgical specimens with anti- CD34. All of the findings were analyzed prospectively and correlated with the clinicopathological findings, which included histological grading, presence of lymph node metastasis, serosal involvement, distant metastasis, tumor, node, metastasis (TNM) staging, and MVD. The statistical analyses used included the Student's t-test and the Spearman rank correlation were performed in SPSS 11.5.

Results

The mean perfusion values and MVD for tumors were as follows: BF (48.14±16.46 ml/100 g/min), BV (6.70±2.95 ml/100 g), MTT (11.75±4.02 s), PS (14.17±5.23 ml/100 g/min) and MVD (41.7±11.53). Moreover, a significant difference in the PS values was found between patients with or without lymphatic involvement (p = 0.038), as well as with different histological grades (p = 0.04) and TNM stagings (p = 0.026). However, BF, BV, MTT, and MVD of gastric cancer revealed no significant relationship with the clinicopathological findings described above (p > 0.05).

Conclusion

The perfusion CT values of the permeable surface could serve as a useful prognostic indicator in patients with advanced gastric cancer.

[The role of computed tomography perfusion in the diagnosis of brain ischaemic stroke]

In recent years, the broad introduction of fast multidetector computed tomography (CT) systems and the availability of commercial software for perfusion analysis have made cerebral perfusion imaging with CT a practical technique for the clinical environment.

AIM AND METHODS

This article reviews the use of CT for imaging cerebral perfusion, highlighting its advantages, disadvantages and limitations, and draws comparisons between perfusion CT and magnetic resonance imaging. The authors performed 96 perfusion CT examinations in the last one and a half years. Future technical developments in multi-slice CT systems may diminish the current limitations of limited spatial coverage and radiation burden. Yet CT is often not perceived as a technique for imaging cerebral perfusion.

CONCLUSIONS

The technique is widely available at low cost, accurate and easy to perform. Perfusion CT is particularly applicable to those clinical circumstances where patients already undergo CT for other reasons, including stroke.

Evaluation of multislice computed tomographic perfusion imaging and computed tomographic angiography on traumatic cerebral infarction

OBJECTIVE

To evaluate the application value of multislice computed tomographic perfusion imaging (MSCTPI) and multislice computed tomographic angiography (MSCTA) on traumatic cerebral infarction.

METHODS

MSCTA was performed on 10 patients who were initially diagnosed as traumatic cerebral infarction by normal conventional computed tomography (NCCT), among whom, 3 patients were examined by MSCTPI simultaneously. Reconstructed images of the intracranial artery were made with techniques of maximum intensity projection (MIP) and volume rendering (VR) from MSCTA scanning data. Then the graph of function of four parameters, regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), mean transit time (MTT), and time to peak (TTP), acquired by the perfusing analysis software was obtained.

RESULTS

Among the 10 patients with traumatic cerebral infarction, 6 showed complex type on NCCT, which depicted abnormality on MSCTA, and 4 showed simple type on NCCT, which had negative results on MSCTA. Among the 4 patients with abnormal great vessels, 2 suffered from stenosis or occlusion of the middle cerebral artery, 1 from spasm of the anterior cerebral artery, and 1 from spasm of the vertebral-basal artery. The image of MSCTPI of 1 patient with massive cerebral infarction on the right cerebral hemisphere confirmed by CT was smaller than those of the other patients, which showed occlusion of the ipsilateral middle cerebral artery on MSCTA. Among the 6 patients whose MSCTA showed no abnormality, 4 showed simple infarction and 2 showed complex infarction. The infarction focus of 5 patients occurred in the basal ganglia and 1 in the splenium of corpus callosum. Among the 2 cases of small cerebral infarction volume on NCCT, one was normal, the other showed hypoperfusion on MSCTPI and was normal on MSCTA.

CONCLUSION

The combination of MSCTPI and MSCTA is very useful for evaluating the change of intracranial artery in ischemic regions and assessing the cerebral hemodynamic information of traumatic cerebral infarction.

Quantitative cerebrovascular reserve measured by acetazolamide-challenged dynamic CT perfusion in ischemic adult Moyamoya disease: initial experience with angiographic correlation

BACKGROUND AND PURPOSE

CT perfusion is a much more readily accessible imaging method to assess cerebral hemodynamic status than single-photon emission CT. We prospectively assessed quantitative cerebrovascular reserve by using acetazolamide (ACZ)-challenged CT perfusion for evaluating hemodynamic impairment in ischemic adult Moyamoya disease and compared it with angiographic findings.

MATERIALS AND METHODS

Sixteen adult patients with ischemic Moyamoya disease and 12 age-matched normal control subjects underwent both ACZ-challenged CT perfusion and digital subtraction angiography. Normalized baseline hemodynamic parameters and their percent changes (PCs) were calculated in 56 hemispheres. We classified the degrees of distal carotid artery stenosis according to modified Suzuki stage and determined the presence of basal Moyamoya vessels (BMVs). The values of normalized parameters and their PCs were compared with angiographic findings.

RESULTS

Normalized baseline mean transit time (MTT) and PC of normalized cerebral blood flow (CBF) were significantly correlated with angiographic stages in all of the vascular territories; however, the correlation coefficient of the normalized baseline MTT was lower than that of the PC of CBF. In the external borderzone and the middle cerebral arterial territory, the hemispheres with extensive BMVs exhibited significantly lower PC values of CBF and significantly higher normalized baseline MTT values than those in hemispheres with diminished BMVs and in normal control subjects.

CONCLUSION

Among the hemodynamic parameters measured by ACZ-challenged CT perfusion, the PC of CBF correlated highly significantly with angiographic stage; however, the normalized baseline CT perfusion parameters showed weak or no significant correlation.

Multiphase CT angiography versus single-phase CT angiography: comparison of image quality and radiation dose

BACKGROUND AND PURPOSE

Conventional CT angiography (CTA) is acquired during only a short interval in the arterial phase, which limits its ability to evaluate the cerebral circulation. Our aim was to compare the image quality and radiation dose of conventional single-phase CTA (SP-CTA) with a multiphase CTA (MP-CTA) algorithm reconstructed from a perfusion CT (PCT) dataset.

MATERIALS AND METHODS

Fifty consecutive patients undergoing head CTA and PCT in 1 examination were enrolled. The PCT dataset was obtained with 40.0-mm-detector coverage, 5.0-mm axial thickness, 80 kilovolt peak (kVp), 180 mA, and 30 mL of contrast medium. MP-CTA was reconstructed from the same PCT dataset with an axial thickness of 0.625 mm by using a new axial reconstruction algorithm. A conventional SP-CTA dataset was obtained with 0.625-mm axial thickness, 120 kVp, 350 mA, and 60 mL of contrast medium. We compared image quality, vascular enhancement, and radiation dose.

RESULTS

SP-CTA and MP-CTA of 50 patients (male/female ratio, 31/19; mean age, 59.25 years) were analyzed. MP-CTA was significantly better than SP-CTA in vascular enhancement (P = .002), in the absence of venous contamination (P = .006), and was significantly higher in image noise (P < .001). MP-CTA used less contrast medium than SP-CTA and could demonstrate hemodynamic information. The effective dose of MP-CTA was 5.73 mSv, which was equal to that in conventional PCT, and it was 3.57 mSv in SP-CTA.

CONCLUSION

It is feasible that MP-CTA may provide both CTA and PCT results. Compared with SP-CTA, MP-CTA provides comparable image quality, better vascular enhancement, hemodynamic information, and more noise with less detail visibility with a lower tube voltage. The radiation dose of MP-CTA is higher than that of SP-CTA, but the dose can be reduced by altering the sampling interval.

Computed tomography assessment of cerebral perfusion using a distributed parameter tracer kinetics model: validation with H(2)((15))O positron emission tomography measurements and initial clinical experience in patients with acute stroke

We describe a distributed parameter (DP) model for tracer kinetic analysis in brain and validate the derived perfusion values with positron emission tomography (PET) scans. The proposed model is applied on actual clinical cases of hemispheric stroke. Nine patients with experienced transient ischaemic attack or minor stroke and a stenosis of the internal carotid artery were referred for computed tomography (CT) and PET imaging. The applicability of the DP model in clinical practice was tested in seven patients with acute stroke who received a baseline perfusion CT study and a noncontrast follow-up CT study after 2.4+/-1.8 days. The mean blood flow (F) value for all patients with carotid stenosis in the pooled data (54 regions of interest (ROIs)) was 37.9+/-11.2 mL/min per 100 g in perfusion CT and 35.6+/-9.8 mL/min per 100 g in perfusion PET imaging [r=0.77 (P=0.00)]. Regression analysis of the pooled ROIs for every patient revealed significant correlation between F values in seven patients [r=0.50 to 0.79 (r(2)-values ranged from 0.45 to 0.79), (0.01 < or = P < or = 0.05)]. Parametric maps that corresponded to all physiologic parameters were generated for every perfusion CT in the patients with acute stroke using the DP model. The ischaemic area was better delineated in F, intravascular blood volume and lag time (t(lag)) maps. The correlation coefficient comparing the visually outlined regions of abnormality between the t(lag) parametric map and the follow-up CT scans was 0.81 (P=0.003). In conclusion, DP physiological model using more realistic pharmacokinetics is feasible in dynamic contrast-enhanced CT of the brain in patients with acute and chronic cerebrovascular disease.

Qualitative aspects of cranial CT perfusion scanning in a mixed neurosurgical patient collective

BACKGROUND

In patients with ischemic stroke, computer tomography (CT) perfusion imaging provides rapid information on the penumbra adjacent to the infarct core. For neurosurgical patients with acute brain injury, the value of CT perfusion is undecided up to now. We present our experience in a series of 78 examinations in 35 patients with acute intracranial pathology.

METHODS

CT perfusion was performed with a Siemens Emotion Duo CT scanner using a single slice at the level of the upper basal ganglia. Color maps of time to peak (TTP), cerebral blood flow (CBF) and cerebral blood volume (CBV) were analyzed according to qualitative criteria. Quantitative evaluation with self-defined regions of interest was not performed due to repeatability problems and inconsistent data.

FINDINGS

TTP showed an interhemispheric difference in 45% and regional prolongation in 16% of the scans. Global TTP was prolonged in 60%, while global CBF was reduced in 43%. Two patients showed hyperemia. A CBF/CBV mismatch, indicating non-infarcted penumbra at risk, was seen in 67%. Six patients with aneurysmal SAH showed reduced CBF, and consecutive angiography confirmed vasospasm in every case.

CONCLUSIONS

CT perfusion scanning gives valuable information at a low risk and with negligible additional time after a routine cranial CT. In our opinion, this modality may have considerable impact on the clinical management of severely brain injured patients in future.

Perfusion computerized tomography can predict pancreatic necrosis in early stages of severe acute pancreatitis

BACKGROUND & AIMS

The mortality rate associated with severe acute pancreatitis (SAP) with necrosis remains high because early prediction of pancreatic necrosis is difficult. We evaluated whether perfusion computerized tomography (CT), which is used to identify early stage ischemia in the brain, could detect ischemic changes in the pancreas in the early stages of SAP and predict development of necrosis.

PATIENTS AND METHODS

Thirty consecutive patients with a diagnosis of SAP according to the Atlanta criteria and whose score was greater than 6 were enrolled in this study. All patients were hospitalized within 3 days after onset of symptoms indicative of acute pancreatitis and underwent perfusion CT. Three weeks later, all patients underwent conventional contrast-enhanced CT to detect progression of their disease.

RESULTS

Perfusion CT showed that 10 of the 30 patients had pancreatic ischemia at the time of diagnosis. Contrast-enhanced CT disclosed that pancreatic necrosis developed in 9 of these 10 patients, but not in the 20 patients who did not have pancreatic ischemia. The sensitivity and specificity of perfusion CT for predicting pancreatic necrosis was calculated to be 100% and 95.3%, respectively.

CONCLUSIONS

Perfusion CT is a useful tool for early detection of ischemic changes in the pancreas that lead to pancreatic necrosis.

Increasing contrast agent concentration improves enhancement in first-pass CT perfusion

BACKGROUND AND PURPOSE

Our aim was to evaluate whether increasing iodine concentration, at a constant total iodine dose, resulted in better brain tissue opacification in patients with acute stroke symptoms during their evaluation by first-pass CT perfusion (CTP).

MATERIALS AND METHODS

One hundred two patients presenting to the emergency department within 3 hours of onset of acute stroke symptoms underwent CTP scanning. Three different concentrations of iodinated nonionic contrast material were used (300, 350, or 400 mg/mL). Total iodine dose (15 g) and injection rate (7 mL/s) were kept constant. There were 25, 53, and 19 patients in the different concentration groups, respectively; 5 patients were excluded due to uncorrectable motion artifacts. CTP scanning was performed at the level of the putamen, and data were analyzed by determining peak opacification for normal gray and white matter, arterial input, and venous output. Mean and SD values were calculated, and 3 concentration groups, stratified by region-of-interest location, were compared by using a single-tailed unpaired t test.

RESULTS

Monotonic increasing peak opacification was observed in all region-of-interest locations. Statistically significant differences were observed between the 300 and 350 mg/mL, 300 and 400 mg/mL, as well as the 350 and 400 mg/mL groups (P<.01) in white matter, gray matter, and the arterial input. Statistical significance was seen in the venous output group between the 300 and 400 mg/mL (P<.005) and 350 and 400 mg/mL (P<.007) groups, but not between the 300 and 350 mg/mL (P=.2) groups.

CONCLUSION

Increasing contrast concentration improves peak opacification of tissue, suggesting that CTP evaluation of patients with acute stroke is better performed with the highest available concentration contrast agent.

Comparison of different iodine concentration contrast media in perfusion computed tomography of the brain: is high iodine concentration useful?

OBJECTIVES

To investigate maximum enhancement and visual map quality in cerebral perfusion computed tomography (PCT) with variation of iodine concentration of contrast media (CM).

MATERIALS AND METHODS

Two groups of 45 patients each, underwent PCT with either 370 mg iodine/mL (30 mL; 6 mL/s) or 300 mg iodine/mL (40 mL; 8 mL/s) CM, respectively, and similar total iodine dose. Parenchymal and vascular enhancement as well as contrast-to-noise ratio of superior sagittal sinus was measured on PCT source images. PCT maps were rated visually with dichotomized scale for diagnostic quality.

RESULTS

Enhancement and contrast-to-noise ratio of the superior sagittal sinus was significantly higher for the 370 mg iodine/mL protocol (P < 0.0002 and P < 0.007), whereas parenchymal enhancement was not significantly different. Diagnostic quality of PCT maps did not differ between both protocols (P < 0.557).

CONCLUSIONS

PCT using 370 mg iodine/mL CM can be reliably performed with reduced injection rate and less total volume enabling smaller diameter of intravenous canula compared with 300 mg iodine/mL CM.

CT perfusion-derived mean transit time predicts early mortality and delayed vasospasm after experimental subarachnoid hemorrhage

BACKGROUND AND PURPOSE

There are limited indicators available to predict cerebral vasospasm in patients with subarachnoid hemorrhage (SAH). The purpose of this study was to determine if CT perfusion-derived hemodynamic parameters are predictors of vasospasm severity and outcome after experimental SAH.

MATERIALS AND METHODS

SAH was induced in 25 New Zealand white rabbits. Cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) were measured with CT perfusion before SAH, within 1 hour after SAH, and on days 2, 4, 7, 9, and 16 after SAH. Basilar artery diameter, measured with CT angiography and neurologic scoring, was also obtained on the same days. Differences between animals with moderate-severe delayed vasospasm (>/=24% basilar artery narrowing) and mild delayed vasospasm (<24% basilar artery narrowing) were investigated with repeated measures analysis of variance. Multiple linear regression analysis was used to investigate the relationship between CT perfusion parameters (CBF, CBV, MTT), basilar artery diameter, and neurologic score.

RESULTS

MTT increase <1 hour after SAH independently predicted mortality within 48 hours of SAH (P < .05). MTT and neurologic deficits were significantly greater with moderate-severe than with mild vasospasm (P < .05). MTT on day 2, but not CBF or CBV, was a significant predictor of subsequent moderate-severe delayed vasospasm (P < .05).

CONCLUSION

In the rabbit model of experimental SAH, the CT-derived hemodynamic parameter MTT on day 0 predicted early mortality, and MTT on day 2 predicted development of moderate-severe delayed vasospasm. MTT was also significantly correlated with arterial diameter and neurologic score.

FIRST-PASS PERFUSION COMPUTED TOMOGRAPHY

OBJECTIVE

To differentiate recurrent tumors from radiation effects and necrosis in patients with irradiated brain tumors using perfusion computed tomographic (PCT) imaging.

METHODS

Twenty-two patients with previously treated brain tumors who showed recurrent or progressive enhancing lesions on follow-up magnetic resonance imaging scans and had a histopathological diagnosis underwent first-pass PCT imaging (26 PCT imaging examinations). Another eight patients with treatment-naïve, high-grade tumors (control group) also underwent PCT assessment. Perfusion maps of cerebral blood volume, cerebral blood flow, and mean transit time were generated at an Advantage Windows workstation using the CT perfusion 3.0 software (General Electric Medical Systems, Milwaukee, WI). Normalized ratios (normalized to normal white matter) of these perfusion parameters (normalized cerebral blood volume [nCBV], normalized cerebral blood flow [nCBF], and normalized mean transit time [nMTT]) were used for final analysis.

RESULTS

Fourteen patients were diagnosed with recurrent tumor, and eight patients had radiation necrosis. There was a statistically significant difference between the two groups, with the recurrent tumor group showing higher mean nCBV (2.65 versus 1.10) and nCBF (2.73 versus 1.08) and shorter nMTT (0.71 versus 1.58) compared with the radiation necrosis group. For nCBV, a cutoff point of 1.65 was found to have a sensitivity of 83.3% and a specificity of 100% to diagnose recurrent tumor and radiation necrosis. Similar sensitivity and specificity were 94.4 and 87.5%, respectively, for nCBF with a cutoff point of 1.28 and 94.4 and 75%, respectively, for nMTT with a cutoff point of 1.44 to diagnose recurrent tumor and radiation necrosis.

CONCLUSION

PCT may aid in differentiating recurrent tumors from radiation necrosis on the basis of various perfusion parameters. Recurrent tumors show higher nCBV and nCBF and lower nMTT compared with radiation necrosis.

Perfusion CT to evaluate the effect of transluminal angioplasty on cerebral perfusion in the treatment of vasospasm after subarachnoid hemorrhage

INTRODUCTION

Delayed ischemic neurologic deficits secondary to vasospasm are a major cause of morbidity and mortality after subarachnoid hemorrhage (SAH). Treatment of vasospasm after SAH is associated with complications, and reliable techniques for evaluating effects of treatment of vasospasm in such patients are warranted. We present the use of perfusion computed tomography (PTC) to evaluate the effect of transluminal percutaneous angioplasty in a with SAH and vasospasm-induced ischemia.

METHODS

Dynamic PCT with deconvolution produced maps of time-to-peak, mean transit time, regional cerebral blood flow, and regional cerebral blood volume, with a computerized automated map of the infarct and penumbra. CT scanners with quadruple detector array were used before and after angioplasty.

RESULTS

Before angioplasty and intraarterial papaverine, PCT showed normal to decreased cerebral blood flow and increased cerebral blood volume and mean transit time in the middle cerebral artery territory of the left hemisphere. After angioplasty and intraarterial papaverine, PCT showed normalization of perfusion parameters.

CONCLUSION

PCT can be a useful technique in monitoring angioplasty treatment effects in patients with vasospasm after SAH.

Structural and functional neuroimaging in mild-to-moderate head injury

Head injury is a major cause of disability and death in adults. Significant developments in imaging techniques have contributed to the knowledge of the pathophysiology of head injury. Although extensive research is available on severe head injury, less is known about mild-to-moderate head injury despite the fact that most patients sustain this type of injury. In this review, we focus on structural and functional imaging techniques in patients with mild-to-moderate head injury. We discuss CT and MRI, including different MRI sequences, single photon emission computed tomography, perfusion-weighted MRI, perfusion CT, PET, magnetic resonance spectroscopy, functional MRI and magnetic encephalography. We outline the advantages and limitations of these various techniques in the contexts of the initial assessment and identification of brain abnormalities and the prediction of outcome.

CT Quantification of Effects of Thalidomide in Patients with Metastatic Renal Cell Carcinoma

OBJECTIVE

Our objective was to use functional CT to evaluate the effects of thalidomide in patients with metastatic renal cell carcinoma.

SUBJECTS AND METHODS

Patients with proven metastatic renal cell carcinoma were examined prospectively with functional CT. Functional CT studies (cine mode, 4 x 5 mm) were performed through the tumor after i.v. administration of a bolus of contrast material before and every 12 weeks after treatment with thalidomide. Quantitative values for blood flow, blood volume, mean transit time, and permeability-surface area product were calculated with commercial software. The average difference in percentage change in functional CT parameters from pretreatment to 12 and 24 weeks after treatment and the median difference in percentage change in functional CT parameters between response groups were assessed. We also tested whether percentage changes in functional CT parameters 12 weeks after treatment correlated with time to progression of disease and size of the perfused lesion.

RESULTS

Sixteen patients with a total of 23 tumors underwent at least one follow-up functional CT examination. Blood flow, blood volume, and permeability-surface area product decreased significantly 12 weeks (-18%, p = 0.0039; -15%, p = 0.0350; -24%, p = 0.0010) and 24 weeks (-28%, p = 0.017; -19%, p = 0.0300; -25%, p = 0.0031) after treatment with thalidomide. Time to progression correlated significantly with percentage change in blood flow (r = -0.34; p = 0.040) and permeability-surface area product (r = -0.36, p = 0.023) at 12 weeks. Responders had a significantly larger decrease in blood flow 12 weeks after treatment than did nonresponders (-29% vs -6%; p = 0.032). We also found a significant correlation between decrease in size of the perfused lesion and percentage decrease in blood flow 12 weeks after treatment (r = 0.50; p = 0.019).

CONCLUSION

Changes in functional CT parameters 12 weeks after treatment may be useful for monitoring the effects of thalidomide and predicting treatment outcome among patients with metastatic renal cell carcinoma. Further study with a larger clinical trial is needed.

Variability of clinical CT perfusion measurements in patients with carotid stenosis

INTRODUCTION

CT perfusion imaging (pCT) may be used to detect and monitor hemodynamic abnormalities due to cerebrovascular disease. The magnitude of variability in clinical measurements has been insufficiently evaluated. The purpose of this study was to measure the long-term variability of clinical pCT measurements in patients with cerebrovascular disease.

METHODS

pCT parameters were calculated for the cerebral hemisphere contralateral to a carotid stenosis before and after stent treatment of stenosis in 33 consecutive patients. Mean transit time (MTT), cerebral blood flow (CBF), and cerebral blood volume (CBV) calculated from pCT data from both a small and large region of interest (ROI) using both manual and automated methods were compared before and after stent treatment. Differences between the first and second measurement were tested for statistical significance with at-test. Variability was calculated as the standard deviation of the differences divided by the mean of the pre- and post-stent treatment values. To adjust for proportional bias, the Bland-Altman analysis was applied.

RESULTS

The differences between the two measurements of MTT, CBF, and CBV averaged 2.5 to 7.7% when a manual method was used and was higher with automatic methods (p > 0.07). The variability of the values was 18% for MTT, 19% for CBV, and 25% for CBF with the large ROI and the manual method of calculation. The magnitude was larger when the small ROI and automatic methods were employed.

CONCLUSION

Longitudinal measurements of MTT, CBV, or CBF by pCT may vary by 20-25%. To detect changes in treatment-related changes in perfusion, pCT studies must be designed to achieve statistical significance based on this variability.

Does perfusion CT enable differentiating Alzheimer's disease from vascular dementia and mixed dementia? A preliminary report

The purpose of the study was to evaluate the usefulness of perfusion CT (pCT) in differentiating Alzheimer's disease (AD) from vascular dementia (VaD) and mixed dementia (MixD). pCT was performed in 41 patients (mean age, 68.3 years): 24 with AD, 8 with VaD, and 9 with MixD. Regional perfusion parameters (rCBF, rCBV, and rMTT) were calculated from 31 ROIs in the grey and white matter of the frontal and temporal lobes, basal ganglia, and internal capsules bilaterally. The obtained data for the subgroups of AD, VaD, and MixD patients were compared statistically.

CONCLUSIONS

On the basis of rCBF and rCBV values, pCT may be a valuable method of distinguishing between AD and VaD but it seems to be of little significance in differentiating MixD from VaD and of no usefulness in distinguishing between AD and MixD.

Dynamic perfusion CT: optimizing the temporal resolution for the calculation of perfusion CT parameters in stroke patients

PURPOSE

To assess the influence of different temporal sampling rates on the accuracy of the results from cerebral perfusion CTs in patients with an acute ischemic stroke.

MATERIAL AND METHODS

Thirty consecutive patients with acute stroke symptoms received a dynamic perfusion CT (LightSpeed 16, GE). Forty millilitres of iomeprol (Imeron 400) were administered at an injection rate of 4 ml/s. After a scan delay of 7s, two adjacent 10mm slices at 80 kV and 190 mA were acquired in a cine mode technique with a cine duration of 49 s. Parametric maps for the blood flow (BF), blood volume (BV) and mean transit time (MTT) were calculated for temporal sampling intervals of 0.5, 1, 2, 3 and 4s using GE's Perfusion 3 software package. In addition to the quantitative ROI data analysis, a visual perfusion map analysis was performed.

RESULTS

The perfusion analysis proved to be technically feasible with all patients. The calculated perfusion values revealed significant differences with regard to the BF, BV and MTT, depending on the employed temporal resolution. The perfusion contrast between ischemic lesions and healthy brain tissue decreased continuously at the lower temporal resolutions. The visual analysis revealed that ischemic lesions were best depicted with sampling intervals of 0.5 and 1s.

CONCLUSION

We recommend a temporal scan resolution of two images per second for the best detection and depiction of ischemic areas.

Convenience of the computed tomography perfusion method for cerebral vasospasm detection after subarachnoid hemorrhage

BACKGROUND

Vasospasm is a frequent complication in the early clinical course after SAH. Although various methods have been used to measure cerebral perfusion including PET, SPECT, xenon CT, and TCD, these require the patients to remain still for a long period. In addition, TCD is operator dependent. The current study aimed to clarify the convenience of CTP for the assessment of cerebral vasospasm caused by SAH.

METHODS

Nineteen patients with SAH aged 44 to 85 years (mean, 64 years) were recruited with informed consent. All patients were treated with the prevailing therapy and underwent CTP on days 6 to 9, followed by DSA and 3D-CTA to detect cerebral vasospasm. In each patient, we measured the MTT, CBF, and CBV. The reliability of CTP data was verified by comparing the data from CTP and xenon CT between the controls, and the average was calculated. Six ROIs were located symmetrically in the frontal, temporal, and occipital lobes.

RESULTS

An MTT value more than 20% greater than the average indicated the progression of cerebral vasospasm, and patients with vasospasm-related infarcts exhibited an MTT more than 47% greater than the mean value (odds ratio, 50). Patients with delayed cerebral infarcts had a significantly lower mean CBF and CBV and higher MTT than patients who did not develop CI.

CONCLUSION

Significant correlations between MTT and CBF values and neurovascular findings were obtained. Computed tomography perfusion can be performed in a short time and on a regular basis, and it therefore has the potential to identify cerebral vasospasm because of SAH.

Current Techniques Used for the Radiologic Assessment of Intracranial Neoplasms

Context.—Radiologic studies are obtained for diagnostic and treatment planning purposes in the evaluation of patients with intracranial neoplasms. These studies are discussed at radiology/pathology working conferences and are often beneficial in the analysis of pathologic specimens for tissue diagnosis. Therefore, clinical pathologists should be aware of the current and evolving imaging techniques that are used in the radiologic assessment of intracranial neoplasms.

Objective.—To describe the imaging techniques used in the assessment of intracranial neoplasms and provide current references.

Data Sources.—We searched PubMed for articles published between 1995 and 2006 and also reviewed several textbooks on intracranial neoplasms, to prepare a discussion of basic modalities such as computed tomography (CT) and magnetic resonance (MR) imaging as well as advanced imaging techniques such as CT and MR angiography and venography, CT and MR perfusion, MR spectroscopy, functional MR imaging, and positron emission tomography.

Conclusions.—Knowledge of currently used imaging techniques for the assessment of intracranial neoplasms will assist the clinical pathologist in communications with neuroradiologists, surgeons, and referring clinicians. This review will also aid the pathologist in understanding the new and rapidly evolving imaging techniques that will likely become the standard of care in the future.

Pixel-by-pixel deconvolution of bolus-tracking data: optimization and implementation

Quantification of haemodynamic parameters with a deconvolution analysis of bolus-tracking data is an ill-posed problem which requires regularization. In a previous study, simulated data without structural errors were used to validate two methods for a pixel-by-pixel analysis: standard-form Tikhonov regularization with either the L-curve criterion (LCC) or generalized cross validation (GCV) for selecting the regularization parameter. However, problems of image artefacts were reported when the methods were applied to patient data. The aim of this study was to investigate the nature of these problems in more detail and evaluate strategies of optimization for routine application in the clinic. In addition we investigated to which extent the calculation time of the algorithm can be minimized. In order to ensure that the conclusions are relevant for a larger range of clinical applications, we relied on patient data for evaluation of the algorithms. Simulated data were used to validate the conclusions in a more quantitative manner. We conclude that the reported problems with image quality can be removed by appropriate optimization of either LCC or GCV. In all examples this could be achieved with LCC without significant perturbation of the values in pixels where the regularization parameter was originally selected accurately. GCV could not be optimized for the renal data, and in the CT data only at the cost of image resolution. Using the implementations given, calculation times were sufficiently short for routine application in the clinic.

Current Concepts in the Management of Intracranial Atherosclerotic Disease

MEDICALLY REFRACTORY, SYMPTOMATIC intracranial atherosclerotic disease has a poor prognosis. Based on the results of the Warfarin-Aspirin Symptomatic Intracranial Disease study, the risk of ipsilateral stroke at 1.8 years is between 13 and 14% in patients with symptomatic intracranial atherosclerosis. Synergistic advances in intracranial angioplasty and stenting, modern neuroimaging techniques, and periprocedural and postprocedural antithrombotic regimens are creating new models for the diagnosis and successful endovascular treatment of intracranial stenosis. In this article, the most recent clinical developments and concepts for the diagnosis and endovascular treatment of intracranial atherosclerotic disease are discussed.

State-of-the-Art Imaging of Acute Stroke

Stroke is a leading cause of mortality and morbidity in the developed world. The goals of an imaging evaluation for acute stroke are to establish a diagnosis as early as possible and to obtain accurate information about the intracranial vasculature and brain perfusion for guidance in selecting the appropriate therapy. A comprehensive evaluation may be performed with a combination of computed tomography (CT) or magnetic resonance (MR) imaging techniques. Unenhanced CT can be performed quickly, can help identify early signs of stroke, and can help rule out hemorrhage. CT angiography and CT perfusion imaging, respectively, can depict intravascular thrombi and salvageable tissue indicated by a penumbra. These examinations are easy to perform on most helical CT scanners and are increasingly used in stroke imaging protocols to decide whether intervention is necessary. While acute infarcts may be seen early on conventional MR images, diffusion-weighted MR imaging is more sensitive for detection of hyperacute ischemia. Gradient-echo MR sequences can be helpful for detecting a hemorrhage. The status of neck and intracranial vessels can be evaluated with MR angiography, and a mismatch between findings on diffusion and perfusion MR images may be used to predict the presence of a penumbra. The information obtained by combining various imaging techniques may help differentiate patients who do not need intravenous or intraarterial therapy from those who do, and may alter clinical outcomes.

Utility of computed tomography perfusion in detection of cerebral vasospasm in patients with subarachnoid hemorrhage

OBJECT

Digital subtraction (DS) angiography is the gold standard for detecting cerebral vasospasm after subarachnoid hemorrhage (SAH). Computed tomography (CT) perfusion is a recently developed modality for the evaluation of cerebral hemodynamics. This study was conducted to evaluate the potential of using CT perfusion to detect vasospasm in patients with SAH.

METHODS

Fourteen patients between the ages of 41 and 66 years with aneurysmal SAH underwent 23 CT perfusion scans for suspected vasospasm. All patients underwent DS angiography within 12 hours of the CT perfusion scans. The presence of vasospasm on CT perfusion images was determined based on qualitative reading using color maps of mean transit time, cerebral blood flow, and cerebral blood volume as criteria. The presence or absence of vasospasm as retrospectively determined using CT perfusion was compared with DS angiography findings. Of the 23 CT perfusion scans performed, 21 (91%) were concordant with angiography findings in predicting the presence or absence of vasospasm. In 15 of 23 scans, the presence of vasospasm was detected on CT perfusion scans and confirmed on DS angiography studies. In two cases, vasospasm was revealed on DS angiography but was not confirmed on CT perfusion. The degree of agreement between CT perfusion and DS angiography for detection of vasospasm was high (K = 0.8, p , 0.0001).

CONCLUSIONS

Computed tomography perfusion is an accurate, reliable, and noninvasive method to detect the presence or absence of vasospasm. It can be used as a tool to help guide the decision to pursue DS angiography with the intent to treat vasospasm.

Cerebral perfusion imaging in vasospasm

Vasospasm following cerebral aneurysm rupture is one of the most devastating sequelae and the most common cause of delayed ischemic neurological deficit (DIND). Because vasospasm also is the most common cause of morbidity and mortality in patients who survive the initial bleeding episode, it is imperative not only to diagnose the condition but also to predict which patients are likely to become symptomatic. The exact pathophysiology of vasospasm is complex and incompletely elucidated. Early recognition of vasospasm is essential because the timely use of several therapeutic interventions can counteract this disease and prevent the occurrence of DIND. However, the prompt implementation of these therapies depends on the ability to predict impending vasospasm or to diagnose it at its early stages. A number of techniques have been developed during the past several decades to evaluate cerebral perfusion, including positron emission tomography, xenon-enhanced computed tomography, single-photon emission computed tomography, perfusion- and diffusion-weighted magnetic resonance imaging, and perfusion computed tomography. In this article, the authors provide a general overview of the currently available perfusion imaging techniques and their applications in treating vasospasm after a patient has suffered a subarachnoid hemorrhage. The use of cerebral perfusion imaging techniques for the early detection of vasospasm is becoming more common and may provide opportunities for early therapeutic intervention to counteract vasospasm in its earliest stages and prevent the occurrence of DINDs.

[Brain perfusion and metabolism imaging techniques]

Due to recent efforts in improving spatial and temporal resolution in imaging techniques, it is now possible to get relevant information about brain perfusion and metabolism in humans. This information can significantly impact on brain pathophysiology, diagnosis assessment and therapy options, particularly in patients having brain ischemia. Among these imaging and metabolism techniques are dynamic perfusion computed tomography, perfusion MRI, positron emission tomography and NMR spectroscopic imaging. The goal of this article is an overview of these four techniques, with their own technical description, advantages and drawbacks. Details are provided about brain parameters given by each technique and their clinical relevance, the accessibility of the technique in the emergency setting and the optimal window to use it during the patient's evolution.

Aneurysmal subarachnoid haemorrhage in a patient with thyrotoxicosis

A case of subarachnoid haemorrhage secondary to rupture of an intracranial aneurysm occurring in a patient with new-onset, frank thyrotoxicosis is described. This unusual case highlights the dilemma of whether to continue beta-blockers such as propanolol for frank thyrotoxicosis, or whether to assign higher priority to maintaining adequate cerebral perfusion pressure in established ischaemic deficit due to vasospasm. In a complicated case such as this, the Maudsley Mentation Test score and perfusion CT scanning are two useful adjuncts for the early detection and evaluation of the course of ischaemic deficit.

Diffusion-weighted and perfusion MR imaging for brain tumor characterization and assessment of treatment response

Diffusion-weighted magnetic resonance (MR) imaging and perfusion MR imaging are advanced techniques that provide information not available from conventional MR imaging. In particular, these techniques have a number of applications with regard to characterization of tumors and assessment of tumor response to therapy. In this review, the authors describe the fundamental principles of diffusion-weighted and perfusion MR imaging and provide an overview of the ways in which these techniques are being used to characterize tumors by helping distinguish tumor types, assess tumor grade, and attempt to determine tumor margins. In addition, the role of these techniques for evaluating response to tumor therapy is outlined.

Cerebral perfusion computerized tomography: influence of reference vessels, regions of interest and interobserver variability

INTRODUCTION

There are still no standardized guidelines for perfusion computerized tomography (PCT) analysis.

METHODS

A total of 61 PCT studies were analyzed using either the anterior cerebral artery (ACA) or the middle cerebral artery (MCA) as the arterial reference, and the superior sagittal sinus (SSS) or the vein of Galen (VG) as the venous reference. The sizes of regions of interest (ROI) were investigated comparing PCT results obtained using a hemispheric ROI combined with vascular pixel elimination with those obtained using five smaller ROIs located over the cortex and basal ganglia. In addition, interobserver variations were explored using a standardized protocol.

RESULTS

MCA-based measurements of cerebral blood flow (CBF) and blood volume (CBV) were in accordance with those obtained with the ACA except in 16 patients with ischemic stroke, in whom CBF was overestimated by the ipsilateral MCA. Venous maximal intensity was significantly lower with the VG when compared with the SSS, resulting in overestimation of CBF and CBV. However, in 13.3% of patients the VG ROI yielded higher maximal intensities than the SSS ROI. There was no difference in PCT results between hemispheric ROI and averaged separate ROI when vascular pixel elimination was used. Finally, interobserver variations were as high as 11% for CBF and 12% for CBV.

CONCLUSION

The present results suggest that pathological rather than anatomical considerations should dictate the choice of the arterial ROI. For venous ROI, although SSS seems to be adequate in most instances, deep cerebral veins may occasionally generate higher maximal intensities and should therefore be selected. Importantly, significant user-dependency should be taken into account.

Arterial Spin Labeling: Benefits and Pitfalls of High Magnetic Field

Arterial spin labeling (ASL) techniques are MR imaging methods designed to measure the endogenous perfusion signal coming from arterial blood by manipulation of its magnetization. These methods are based on the subtraction of two consecutively acquired images: one acquired after preparation of the arterial blood magnetization upstream to the area of interest, and the second without any manipulation of its arterial magnetization. The subtraction of both images provides information on the perfusion of the tissue present in the slice of interest. Because ASL is a very low SNR technique, the shift from 1.5 T to 3.0 T should be regarded as a great way to increase signal-to-noise ratio (SNR). Furthermore, the concomitant increase in blood T(1) should improve the SNR of ASL further. Other effects related to poorer magnetic filed homogeneities and reduced T(2) relaxation times, however, will counterbalance both effects partially. In this article, the pros and cons of the use of ASL at high field are summarized, after a brief description of the major techniques used and their theoretical limitations. Finally, a summary of the few existing dedicated ASL perfusion techniques available are presented.

A distributed parameter model of cerebral blood-tissue exchange with account of capillary transit time distribution

Quantitative estimates of physiological parameters associated with cerebral blood flow can be derived from the analysis of dynamic contrast-enhanced (DCE) images, using an appropriate model of the underlying tissue impulse residue function. The theoretical formulation of a distributed parameter model of tissue microcirculation, which accounts for the effects of capillary permeability and transit time distribution, is presented here. This model considers a statistical distribution of capillary-tissue units, each described by a distributed parameter model that accounts for convective transport within the capillary and transcapillary axial diffusion. Monte Carlo simulations were performed to study the confidence of the parameter estimates, and the model was used to analyze DCE CT images of patient study cases with metastatic cerebral tumors. The tumors were found to yield significantly higher estimates than normal tissues for the parameters associated with the extravasation of tracer and for the standard deviation of capillary transit times. The proposed model can be used with DCE imaging to study the microcirculatory characteristics of cerebral tumors.

CT perfusion as a useful tool in the evaluation of leuko-araiosis

Background

Leuko-araiosis (LA) and dementia are common geriatric conditions but their pathogenesis and clinical significance are not completely understood. An evaluation of CT perfusion (CTP) in both these conditions can further enhance the understanding of these diseases.

Methods

Twenty-one patients with LA and 21 age-matched controls were studied with CTP and assessed for their cognitive function. The subjects were classified into four groups: Group 1, with LA (n = 21); Group 2, without LA (n = 21); Group 3, with dementia (n = 7); Group 4, without dementia (n = 11). The mean cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) values were compared between groups 1 and 2, while mean CBF values were compared between groups 3 and 4.

Results

Mean white matter CBF was considerably reduced in patients with LA in the frontal region by 42% (p = 0.000), basal ganglia by 37% (p = 0.000) and occipital region by 18% (p = 0.019). The mean white matter CBV was reduced in patients with LA in the frontal region by 36% (p = 0.000) and basal ganglia by 28% (p = 0.017). The mean white matter CBF was dramatically reduced in patients with dementia in the frontal region by 44% (p = 0.000), basal ganglia by 32% (p = 0.038) and occipital regions by 24% (p = 0.001).

Conclusion

The CTP showed reduced white matter CBF and CBV in patients with LA. This is consistent with chronic ischemia as the pathogenesis of LA. The CTP is also a potentially important technique in the diagnosis and management of dementia, because of its ability to reveal cerebral hypoperfusion.

Evaluation of Cerebral Hemodynamics With Computed Tomography Perfusion Using Gadolinium as an Alternative to Iodinated Contrast

Computed tomography (CT) perfusion is traditionally performed using iodinated contrast, but this can be problematic in patients with impaired renal function or contrast allergy. We report a case of a 63-year-old man whose medical history was complicated by chronic renal failure, which was exacerbated after placement of a left cervical internal carotid artery stent by 70% stenosis and left hemisphere perfusion deficit. On a follow-up clinic visit, because of the patient s chronic renal failure, CT perfusion was performed successfully using gadolinium without further renal complications.

Cerebral blood flow monitoring in clinical practice

The brain depends on a continuous flow of blood to provide it with oxygen and glucose needed to maintain normal function and structural integrity, thus cerebral blood flow is normally tightly regulated. A decrease in cerebral blood flow to ischemic levels may be tolerated for only minutes to hours, depending on the severity of the ischemia. If cerebral blood flow ceases completely, brain cell death occurs within minutes. A variety of conditions are encountered clinically, such as stroke or traumatic brain injury, where an actual or potential alteration in cerebral blood flow puts the brain at risk for ischemia and infarction. In this article, the physiology of cerebral blood flow will be presented as a basis for understanding cerebral blood flow regulation and the rationale for clinical interventions to optimize cerebral blood flow. Techniques currently available to assess cerebral blood flow and clinical situations in which cerebral blood flow is measured will be discussed. Clinical interventions will be presented briefly.

Novel approach to the measurement of absolute cerebral blood volume using vascular-space-occupancy magnetic resonance imaging

Quantitative determination of cerebral blood volume (CBV) is important for understanding brain physiology and pathophysiology. In this work, a novel approach is presented for accurate measurement of absolute CBV (aCBV) using vascular-space-occupancy (VASO) MRI, a blood-nulling pulse sequence, in combination with the T(1) shortening property of Gd-DTPA. Two VASO images with identical imaging parameters are acquired before and after contrast agent injection, resulting in a subtracted image that reflects the amount of blood present in the brain, i.e., CBV. With an additional normalizing factor, aCBV in units of milliliters of blood per 100 mL of brain can be estimated. Experimental results at 1.5 and 3 T systems showed that aCBV maps with high spatial resolution can be obtained with high reproducibility. The averaged aCBV values in gray and white matter were 5.5 +/- 0.2 and 1.4 +/- 0.1 mL of blood/100 mL of brain, respectively. Compared to dynamic susceptibility contrast techniques, VASO MRI is based upon a relatively straightforward theory and the calculation of CBV does not require measurement of an arterial input function. In comparison with previous pre/postcontrast difference approaches, VASO MRI provides maximal signal difference between pre- and postcontrast situation and does not require the use of whole blood for signal normalization.