Optimal sequence timing of CT angiography and perfusion CT in patients with stroke

Contrast Bolus Interference in a Multimodal CT Stroke Protocol

BACKGROUND AND PURPOSE

Whether CTP is performed before or after CTA varies within multimodal CT stroke protocols. CTA after CTP might show venous filling, and CTP metrics might be disturbed by prior CTA. Therefore, we compared CTP metrics conducted before and after CTA in a large cohort of patients with stroke and analyzed interferences of the CTA bolus with the CTP measurement.

MATERIALS AND METHODS

We analyzed 1980 patients (368 patients with CTP performed before CTA [group A] versus 1612 patients with CTP performed after [group B]) in a retrospective study. Mean curves, histograms of CTP baseline Hounsfield units, CBF, CBV, time-to-maximum, hypoperfusion, and core volumes were calculated using the software VEOcore. CTA and CTP interferences were analyzed, and a detection and correction method was proposed.

RESULTS

Mean CTP baseline values were significantly different in both groups (41 versus 45 HU within the groups A and B, respectively). However, perfusion metrics, hypoperfusion, and core volumes yielded no significant differences. In 49 patients, the descending flank of the CTA bolus interfered with the baseline of the CTP measurement, leading to erroneously low CBV values. These errors vanished when a correction method was applied.

CONCLUSIONS

CTP can be reliably performed after CTA without a relevant net effect on perfusion metrics. However, when measuring CTP after CTA, either a short pause on the order of 30 seconds should be observed or an appropriate correction method should be applied. It may help to avoid excluding patients from mechanical thrombectomy by overestimating infarct cores.

Single rotation CTA of extracranial carotids integrated with cerebral CTP provides sufficient quality for decision making in patients with ischaemic stroke

PURPOSE

Large volume computed tomography scanners with 16 cm Z-axis single rotation coverage enable joggle-mode scanning of cerebral computed tomography perfusion and single rotation computed tomography angiography of cervical arteries. Our study aims to evaluate the feasibility of scanning cervical arteries, acquired with single rotation computed tomography angiography during computed tomography perfusion in ischaemic stroke patients.

MATERIALS AND METHODS

A total of 143 patients were scanned with a single contrast medium injection of 60 ml. Hounsfield units of the cervical arteries and veins were objectively measured and carotid bifurcations were subjectively reviewed. The incidence of artefacts and supra-aortic vessel coverage was recorded.

RESULTS

Single rotation computed tomography angiography of the neck demonstrated supra-aortic vessels to their origins in 58 (40.6%) patients. Ninety-nine per cent (1140/1152) of arterial segments were adequately opacified (≥150 Hounsfield units). Arteries were adequately contrasted compared to veins in 81.3% (915/1126) of segments. However, the opacification was reversed in 14.0% (158/1126) of segments, indicating a delayed timing of acquisition; 95.5% (273/286) of carotid bifurcations were of good image quality. Measurement of internal carotid artery stenosis in single rotation computed tomography angiography according to the North American Symptomatic Carotid Endarterectomy Trial correlated well with digital subtraction angiography (R=0.87, P<0.05). Significant artefacts resulted from metal/dental implants (10.5%), contrast in central veins (7.7%) and the shoulder region (4.9%).

CONCLUSION

Single rotation computed tomography angiography of the neck incorporated into cerebral computed tomography perfusion with single contrast medium administration revealed adequate image quality for further decision-making in our patient sample. The main drawbacks were inadequate coverage of supra-aortic arteries and possible delay in timing of the joggle.

Diagnostic accuracy of computed tomography perfusion in the prediction of haemorrhagic transformation and patient outcome in acute ischaemic stroke: A systematic review and meta-analysis

Purpose

The aim of this systematic review and meta-analysis is to determine the diagnostic accuracy of computed tomography brain perfusion in the prediction of haemorrhagic transformation and patient outcome in acute ischaemic stroke.

Method

Electronic databases and grey literature published over the last 10 years related to healthcare and radiology were searched using the key terms: 'computed tomography perfusion', 'haemorrhagic transformation', 'acute ischaemic stroke', 'functional outcome' and their synonyms using both UK and American spellings. Inclusion criteria were: sample size at least 30 patients, original research, evaluate ability of computed tomography perfusion to predict haemorrhagic transformation, reports diagnostic accuracy or provide relevant data for a 2 × 2 contingency table, use follow-up non-contrast computed tomography (NCCT) or magnetic resonance imaging as reference standard.

Findings

Twelve studies were included in the review; studies cover a total of 808 patients. Haemorrhagic transformation occurred in 30.2% of patients. Pooled sensitivity and specificity were 85.9% (95% CI; 65-97%), 73.9% (95% CI; 45-92%) and accuracy of 79.1% (95% CI; 57-98%). Pooled NPV was 92.9% with a high false positive rate (19.8%), which could be explained in terms of outcome classification, acquisition artefact and computed tomography perfusion processing algorithms.

Discussion

This review evaluated the importance of using pre-defined threshold measurement for optimal prediction of HT, the relevance of patient pre-treatment clinical parameters to HT occurrence, the CTP parameters and the measurements that are independent predictors of HT, the significance of rtPA rather as an exacerbator of HT and the impact of both minor and major HT/PH on patient 2⁰ functional outcome.

Conclusion

Computed tomography perfusion has a high sensitivity and moderately high specificity for prediction of haemorrhagic transformation in acute ischaemic stroke. Pre-treatment clinical decision making requires consideration of clinical factors in addition to imaging findings. This systematic review and meta-analysis highlights that pre-treatment computed tomography perfusion adds to clinical confidence by predicting potential for haemorrhage, both in thrombolysed and un-thrombolysed patients, and also influences decisions about alternative treatments for acute ischaemic stroke patients.

Imaging in neurointerventional stroke treatment: review of the recent trials and what your neurointerventionalist wants to know from emergency radiologists

Stroke is one of the leading causes of death and disability worldwide. Standard treatment for stroke is intravenous (IV) injection of tissue plasminogen activator (t-PA) rapidly after symptom onset. However, there are limitations of IV t-PA treatment, such as a short time window for administration and risk for hemorrhage. Recent trials have demonstrated the benefit of endovascular treatment when added to standard treatment to improve outcomes for patients. Advanced imaging was utilized in some trials to identify patients with proximal intracranial occlusion to target for endovascular reperfusion therapy, and to exclude patients with large infarct cores or poor collateral circulation who would not be expected to benefit from intervention. This article summarizes the use of imaging in recent stroke trials in details, provides a stroke imaging protocol, and provides tips which radiologists should know to help their neurointerventionalists.

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.

Optimal Computed Tomographic Perfusion Scan Duration for Assessment of Acute Stroke Lesion Volumes

BACKGROUND AND PURPOSE

The minimal scan duration needed to obtain reliable lesion volumes with computed tomographic perfusion (CTP) has not been well established in the literature.

METHODS

We retrospectively assessed the impact of gradual truncation of the scan duration on acute ischemic lesion volume measurements. For each scan, we identified its optimal scan time, defined as the shortest scan duration that yields measurements of the ischemic lesion volumes similar to those obtained with longer scanning, and the relative height of the fitted venous output function at its optimal scan time.

RESULTS

We analyzed 70 computed tomographic perfusion scans of acute stroke patients. An optimal scan time could not be determined in 11 scans (16%). For the other 59 scans, the median optimal scan time was 32.7 seconds (90th percentile 52.6 seconds; 100th percentile 68.9 seconds), and the median relative height of the fitted venous output function at the optimal scan times was 0.39 (90th percentile 0.02; 100th percentile 0.00). On the basis of a linear model, the optimal scan time was T₀ plus 1.6 times the width of the venous output function (P<0.001; R²=0.49).

CONCLUSIONS

This study shows how the optimal duration of a computed tomographic perfusion scan relates to the arrival time and width of the contrast bolus. This knowledge can be used to optimize computed tomographic perfusion scan protocols and to determine whether a scan is of sufficient duration. Provided a baseline (T₀) of 10 seconds, a total scan duration of 60 to 70 seconds, which includes the entire downslope of the venous output function in most patients, is recommended.