Accuracy of CT cerebral perfusion in predicting infarct in the emergency department: lesion characterization on CT perfusion based on commercially available software

Abstract

This study aims to assess the diagnostic accuracy of a single vendor commercially available CT perfusion (CTP) software in predicting stroke. A retrospective analysis on patients presenting with stroke-like symptoms within 6 h with CTP and diffusion-weighted imaging (DWI) was performed. Lesion maps, which overlays areas of computer-detected abnormally elevated mean transit time (MTT) and decreased cerebral blood volume (CBV), were assessed from a commercially available software package and compared to qualitative interpretation of color maps. Using DWI as the gold standard, parameters of diagnostic accuracy were calculated. Point biserial correlation was performed to assess for relationship of lesion size to a true positive result. Sixty-five patients (41 females and 24 males, age range 22–92 years, mean 57) were included in the study. Twenty-two (34 %) had infarcts on DWI. Sensitivity (83 vs. 70 %), specificity (21 vs. 69 %), negative predictive value (77 vs. 84 %), and positive predictive value (29 vs. 50 %) for lesion maps were contrasted to qualitative interpretation of perfusion color maps, respectively. By using the lesion maps to exclude lesions detected qualitatively on color maps, specificity improved (80 %). Point biserial correlation for computer-generated lesions (Rpb = 0.46, p < 0.0001) and lesions detected qualitatively (Rpb = 0.32, p = 0.0016) demonstrated positive correlation between size and infarction. Seventy-three percent (p = 0.018) of lesions which demonstrated an increasing size from CBV, cerebral blood flow, to MTT/time to peak were true positive. Used in isolation, computer-generated lesion maps in CTP provide limited diagnostic utility in predicting infarct, due to their inherently low specificity. However, when used in conjunction with qualitative perfusion color map assessment, the lesion maps can help improve specificity.

Perfusion CT in acute stroke: effectiveness of automatically-generated colour maps

“…who had undergone CT follow-up, the majority was already manifesting a significant clinical onset, which was highly predictive of CT positivity. 2 When analyzing the concordance between the qualitative analysis of the colour maps and the software-generated maps in reference to ischaemic penumbra areas, in one patient no concordance was highlighted; this was probably owing to the fact that the examination was slightly invalidated by motion artefacts and the software was therefore less reliable in the elaboration of the software-generated maps. It is worth remembering that among the most frequent causes of FN in the software-generated maps, there are small lacunar strokes, the coverage of the cerebral parenchyma and the motion artefacts.…”

“…pCT has been enforced in association with CT arteriography and unenhanced CT in order to identify patients eligible for revascularization in the context of an acute stroke. 2 On this basis, the concept of "time is brain" has been challenged by the ideas of "pathophysiology is brain" and "imaging is brain". 3,4 Dedicated software provide pCT maps that can be used in the evaluation of the vitality of ischaemic tissues: while the infarcted core typically shows a uniform decrease in cerebral blood flow (CBF) and cerebral blood volume (CBV), the penumbra shows a reduction of the CBF value with a preserved or even increased CBV due to the vasodilation of the precapillary arteries and venous obstruction.…”

Exposing Hidden Truncation-Related Errors in Acute Stroke Perfusion Imaging

“…This minimum duration was chosen for 2 reasons: First, 39.5 seconds was the shortest scan duration for which perfusion measurements incorporated at least 9 data points for all patients, thereby avoiding noisier measurements obtained from only a few data points. Second, perfusion studies have used scan durations as short as 40 seconds postinjection, 6,11 and, with our TR of 1.5 seconds, the available scan duration closest to 40 seconds was 39.5 seconds. Linear regression analyses were performed between each of these 11 hemodynamic measurements and scan duration, and against the base-10 logarithm of scan duration.…”

“…Bolus injections typically take at least 5 seconds, and injecting the larger volumes of contrast used for CTP may take 10 seconds or longer. 6,7 After injection, the bolus travels to ischemic brain tissue via stenotic arteries and/or circuitous collateral pathways, potentially lengthening the average arm-to-brain transit time to 35 seconds or more. 8 Dispersion may cause some components of the bolus to arrive far later.…”

“…In comparison, CTP and MRP scans may be as short as 40 seconds. 6,11 Therefore, the parametric perfusion maps that are used for clinical interpretation may be derived from severely truncated concentration data.…”