Optimal brain perfusion CT coverage in patients with acute middle cerebral artery stroke

Abnormalities on Perfusion CT and Intervention for Intracranial Hypertension in Severe Traumatic Brain Injury

The role of invasive intracranial pressure (ICP) monitoring in patients with severe traumatic brain injury (STBI) remain unclear. Perfusion computed tomography (CTP) provides crucial information about the cerebral perfusion status in these patients. We hypothesised that CTP abnormalities would be associated with the severity of intracranial hypertension (ICH). To investigate this hypothesis, twenty-eight patients with STBI and ICP monitors were investigated with CTP within 48 h from admission. Treating teams were blind to these results. Patients were divided into five groups based on increasing intervention required to control ICH and were compared. Group I required no intervention above routine sedation, group II required a single first tier intervention, group III required multiple different first-tier interventions, group IV required second-tier medical therapy and group V required second-tier surgical therapy. Analysis of the results showed demographics and injury severity did not differ among groups. In group I no patients showed CTP abnormality, while patients in all other groups had abnormal CTP (p = 0.003). Severe ischaemia observed on CTP was associated with increasing intervention for ICH. This study, although limited by small sample size, suggests that CTP abnormalities are associated with the need to intervene for ICH. Larger scale assessment of our results is warranted to potentially avoid unnecessary invasive procedures in head injury patients.

CT-based Techniques for Brain Perfusion

Recent rapid advances in endovascular treatment for acute ischemic stroke highlight the crucial role of neuroimaging especially multimodal computed tomography (CT) including CT perfusion in stroke triage and management decisions. With an increasing focus on changes in cerebral physiology along with time-based matrices in clinical decisions for acute ischemic stroke, CT perfusion provides a rapid and practical modality for assessment and identification of salvageable tissue at risk and infarct core and provides a better understanding of the changes in cerebral physiology. Although there are challenges with the lack of standardization and accuracy of quantitative assessment, CT perfusion is evolving as a cornerstone for imaging-based strategies in the rapid management of acute ischemic stroke.

Perfusion computed tomography: 4 cm versus 8 cm coverage size in subjects with chronic carotid artery stenosis

OBJECTIVE

The impact of coverage size on global cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time to peak (TTP) parameters has not been investigated in patients with chronic carotid artery stenosis.

METHODS

63 patients with stenosis of >70% within a single internal carotid artery and neurological symptoms were randomly assigned to two well-matched groups. Differences in CT perfusion scan over a 4 cm or 8 cm range of the brain were compared between the two groups.

RESULTS

The CBF and CBV values were higher in the 4 cm coverage size than in the 8 cm coverage size (by 14.7 and 10.7% on the ipsilateral side and 17.2 and 7.8% on the contralateral side, respectively; all p < 0.001). The MTT value was higher in the 4 cm coverage size than in the 8 cm coverage size on the ipsilateral side (9.6%; p < 0.001). There was no difference between MTT values in the contralateral size. There were no differences between TTP values on the ipsilateral and contralateral sides. The relative indices rMTT and rTTP were higher in the 4 cm coverage size than in the 8 cm coverage size (8.2%, p < 0.001, and 1.1%, p < 0.005, respectively).

CONCLUSION

Absolute CBF and CBV values and relative rMTT and rTTP indices in patients with low CBF and low CBV are highly dependent on coverage size. We recommend using a 4 cm coverage size to assess global cerebral perfusion parameters owing to better accuracy and quicker post-processing.

ADVANCES IN KNOWLEDGE

To the best of our knowledge, this is the first article to compare the influence of 4 cm vs 8 cm coverage size on cerebral perfusion parameters such as CBF, CBV, MTT and TTP in subjects with chronic carotid artery stenosis.

Multimodal imaging in acute ischemic stroke

OPINION STATEMENT

Recent years have seen the development of novel neuroimaging techniques whose roles in the management of acute stroke are sometimes confusing and controversial. This may be attributable in part to a focus on establishing simplified algorithms and terminology that omit consideration of the basic pathophysiology of cerebral ischemia and, consequently, of the full potential for optimizing patients' care based upon their individual imaging findings. This review begins by discussing cerebral hemodynamic physiology and of the effects of hemodynamic disturbances upon the brain. Particular attention will be paid to the hemodynamic measurements and markers of tissue injury that are provided by common clinical imaging techniques, with the goal of enabling greater confidence and flexibility in understanding the potential uses of these techniques in various clinical roles, which will be discussed in the remainder of the review.

Radiation doses of cerebral blood volume measurements using C-arm CT: A phantom study

BACKGROUND AND PURPOSE

Parenchymal blood volume measurement by C-arm CT facilitates in-room peritherapeutic perfusion evaluation. However, the radiation dose remains a major concern. This study aimed to compare the radiation dose of parenchymal blood volume measurement using C-arm CT with that of conventional CTP using multidetector CT.

MATERIALS AND METHODS

A biplane DSA equipped with C-arm CT and a Rando-Alderson phantom were used. Slab parenchymal blood volume (8-cm scanning range in a craniocaudal direction) and whole-brain parenchymal blood volume with identical scanning parameters, except for scanning ranges, were undertaken on DSA. Eighty thermoluminescent dosimeters were embedded into 22 organ sites of the phantom. We followed the guidelines of the International Commission on Radiation Protection number 103 to calculate the effective doses. For comparison, 8-cm CTP with the same phantom and thermoluminescent dosimeter distribution was performed on a multidetector CT. Two repeat dose experiments with the same scanning parameters and phantom and thermoluminescent dosimeter settings were conducted.

RESULTS

Brain-equivalent dose in slab parenchymal blood volume, whole-brain parenchymal blood volume, and CTP were 52.29 ± 35.31, 107.51 ± 31.20, and 163.55 ± 89.45 mSv, respectively. Variations in the measurement of an equivalent dose for the lens were highest in slab parenchymal blood volume (64.5%), followed by CTP (54.6%) and whole-brain parenchymal blood volume (29.0%). The effective doses of slab parenchymal blood volume, whole-brain parenchymal blood volume, and CTP were 0.87 ± 0.55, 3.91 ± 0.78, and 2.77 ± 1.59 mSv, respectively.

CONCLUSIONS

The dose measurement conducted in the current study was reliable and reproducible. The effective dose of slab parenchymal blood volume is about one-third that of CTP. With the advantages of on-site and immediate imaging availability and saving procedural time and patient transportation, slab parenchymal blood volume measurement using C-arm CT can be recommended for clinical application.

Comparison of CT and MR imaging in ischemic stroke

BACKGROUND

Cerebrovascular disease represents a major source of global mortality and morbidity. Imaging examinations play a critical role in the management of stroke patients, from establishing the initial diagnosis to determining and guiding further treatment.

METHODS

In this article, current CT and MRI methods employed in the management of stroke patients are reviewed, with an emphasis on ischemic stroke.

RESULTS

The advantages and disadvantages of these techniques are discussed, a number of cases emphasizing key points are presented, and a comparison between modern CT and MRI techniques is outlined.

CONCLUSION

The major drawback of CT is the high radiation dose, while in MRI it is the more complicated and time-consuming aspect of the examination.

MAIN MESSAGES

• Cerebrovascular disease represents a major source of global mortality and morbidity • Imaging examinations play a critical role in the management of stroke patients • The penumbra may be seen with both CT and MRI; however, this concept may be overly simplistic • The major drawback of CT is the high radiation dose, while MRI is a more complicated examination.

Neuroimaging in acute stroke: choosing the right patient for neurointervention

Although the non-contrast computed tomography head continues as the sole mandatory imaging technique before intravenous thrombolysis, the increased availability of advanced infarct/penumbral imaging techniques and confidence in their use have led many to adopt them into routine practice--most particularly before intra-arterial interventions. Computed tomography versus magnetic resonance-based routes to imaging the cerebral vasculature, cell death, and parenchymal perfusion have differing advantages in terms of speed, availability, exposures to contrast and radiation, sensitivity, and resolution. Continued refinement and future developments, such as the ability to quantitate perfusion, promise to lead to tailored treatment protocols that respect the individual variations in anatomy, physiology, and pathology. This should lead both to an extension of treatment to patients currently excluded by rigid time windows and the avoidance of futile therapies and their associated morbidities.

Standardization of Stroke Perfusion CT for Reperfusion Therapy

With the advances in terms of perfusion imaging, the "time is brain" approach used for acute reperfusion therapy in ischemic stroke patients is slowly being replaced by a "penumbra is brain" or "imaging is brain" approach. But the concept of penumbra-guided reperfusion therapy has not been validated. The lack of standardization in penumbral imaging is one of the main contributing factors for this absence of validation. This article reviews the issues underlying the lack of standardization of perfusion-CT for penumbra imaging, and offers avenues to remedy this situation.

Dynamic CT perfusion imaging for the detection of crossed cerebellar diaschisis in acute ischemic stroke

OBJECTIVE

Although the detection of crossed cerebellar diaschisis (CCD) by means of different imaging modalities is well described, little is known about its diagnosis by computed tomography perfusion (CTP) imaging. We investigated the detection rate of CCD by CTP imaging and the factors related to CCD on CTP images in patients with acute ischemic stroke.

MATERIALS AND METHODS

CT perfusion maps of cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), and time-to-peak (TTP) obtained from 81 consecutive patients affected by an acute ischemic stroke were retrospectively reviewed. Whole-brain perfusion maps were obtained with a multichannel CT scanner using the toggling-table technique. The criteria for CCD was a unilateral supratentorial ischemic lesion and an accompanying decrease in perfusion of the contralateral cerebellar hemisphere on the basis of CTP maps by visual inspection without a set threshold. Maps were quantitatively analyzed in CCD positive cases.

RESULTS

The criteria for CCD were fulfilled in 25 of the 81 cases (31%). Detection rates per CTP map were as follows: MTT (31%) > TTP (21%) > CBF (9%) > CBV (6%). Supratentorial ischemic volume, degree of perfusion reduction, and infratentorial asymmetry index correlated strongly (R, 0.555-0.870) and significantly (p < 0.05) with each other in CCD-positive cases.

CONCLUSION

It is possible to detect CCD on all four of the CTP-based maps. Of these maps, MTT is most sensitive in detecting CCD. Our data indicate that CTP imaging is a valid tool for the diagnosis of CCD in patients affected by an acute hemispheric stroke.

Porcine ex vivo liver phantom for dynamic contrast-enhanced computed tomography: development and initial results

OBJECTIVES

: To demonstrate the feasibility of developing a fixed, dual-input, biologic liver phantom for dynamic contrast-enhanced computed tomography (CT) imaging and to report initial results of use of the phantom for quantitative CT perfusion imaging.

MATERIALS AND METHODS

: Porcine livers were obtained from completed surgical studies and perfused with saline and fixative. The phantom was placed in a body-shaped, CT-compatible acrylic container and connected to a perfusion circuit fitted with a contrast injection port. Flow-controlled contrast-enhanced imaging experiments were performed using 128-slice and 64-slice dual-source multidetector CT scanners. CT angiography protocols were used to obtain portal venous and hepatic arterial vascular enhancement, reproduced over a period of 4 to 6 months. CT perfusion protocols were used at different input flow rates to correlate input flow with calculated tissue perfusion, to test reproducibility, and to determine the feasibility of simultaneous dual-input liver perfusion. Histologic analysis of the liver phantom was also performed.

RESULTS

: CT angiogram 3-dimensional reconstructions demonstrated homogenous tertiary and quaternary branching of the portal venous system to the periphery of all lobes of the liver as well as enhancement of the hepatic arterial system to all lobes of the liver and gallbladder throughout the study period. For perfusion CT, the correlation between the calculated mean tissue perfusion in a volume of interest and input pump flow rate was excellent (R = 0.996) and color blood flow maps demonstrated variations in regional perfusion in a narrow range. Repeat perfusion CT experiments demonstrated reproducible time-attenuation curves, and dual-input perfusion CT experiments demonstrated that simultaneous dual input liver perfusion is feasible. Histologic analysis demonstrated that the hepatic microvasculature and architecture appeared intact and well preserved at the completion of 4 to 6 months of laboratory experiments and contrast-enhanced imaging.

CONCLUSIONS

: We have demonstrated successful development of a porcine liver phantom using a flow-controlled extracorporeal perfusion circuit. This phantom exhibited reproducible dynamic contrast-enhanced CT of the hepatic arterial and portal venous system over a 4- to 6-month period.

Brain perfusion CT for acute stroke using a 256-slice CT: improvement of diagnostic information by large volume coverage

OBJECTIVES

To compare a 256-slice CT with a simulated standard CT for brain CT perfusion (CTP).

METHODS

CTP was obtained in 51 patients using a 256-slice CT (128 detector rows, flying z-focus, 8-cm detector width, 80 kV, 120mAs, 20 measurements, 1 CT image/2.5 s). Signal-to-noise ratios (SNR) were compared in grey and white matter. Perfusion maps were evaluated for cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) in hypoperfused areas and corresponding contralateral regions. Two reconstructed 10-mm slices for simulation of a standard CT (SDCT) were compared with the complete data sets (large-volume CT, LVCT).

RESULTS

Adequate image quality was achieved in 50/51 cases. SNR were significantly different in grey and white matter. A perfusion deficit was present in 27 data sets. Differences between the hypoperfusions and the control regions were significant for MTT and CBF, but not for CBV. Three lesions were missed by SDCT but detected by LVCT; 24 lesions were covered incompletely by SDCT, and 6 by LVCT. 21 lesions were detected completely by LVCT, but none by SDCT.

CONCLUSIONS

CTP imaging of the brain using an increased detector width can detect additional ischaemic lesions and cover most ischaemic lesions completely.

Advantages of extended brain perfusion computed tomography: 9.6 cm coverage with time resolved computed tomography-angiography in comparison to standard stroke-computed tomography

OBJECTIVE

Recent technical developments have led to an extension of perfusion computed tomography (PCT) scan range to cover nearly the entire brain and to reconstruct time resolved (4d) CT-angiography (CTA) datasets from the PCT data. The purpose of this study was to compare the results of simulated standard PCT and extended PCT with 4d-CTA.

MATERIALS AND METHODS

Extended multimodal stroke CT (unenhanced cranial CT, CTA, and PCT) was acquired in 72 patients. PCT images with a scan coverage of 9.6 cm in the z-axis, simulated 2 cm PCT images at the level of the basal ganglia comparable to standard PCT, standard supra-aortic CTA, and 4d-CTA images were reconstructed. Two readers assessed the PCT image quality as well as pathologic findings in extended and simulated PCT, CTA, and 4d-CTA. The brain was divided into 4 axial segments. The independent samples t test was applied to test differences between data for significance.

RESULTS

In 75.0% of all patient exams, pathologic findings were observed in the PCT; these were located in 138 brain segments. In 24.1% of all 54 exams with pathologic PCT findings, the pathology would have been missed on standard PCT. The longer scan coverage resulted in a different final diagnosis in 34.7% of all exams. Quality of the PCT parameter maps was on average very good both for the supratentoric and the infratentoric brain areas (4.28 and 4.18, respectively, on a 5-point scale). In 90% of all exams with pathologic changes in the CTA, these abnormalities were also noted on 4d-CTA. In only 2.8% of all cases, the additional time resolution of the 4d-CTA provided additional information.

CONCLUSION

Extending the scan coverage of PCT from 2 cm to 9.6 cm led to an augmentation of clinically important information in the imaging of acute stroke.