Accuracy of Non-Enhanced CT in Detecting Early Ischemic Edema Using Frequency Selective Non-Linear Blending

Abstract

PurposeIschemic brain edema is subtle and hard to detect by computed tomography within the first hours of stroke onset. We hypothesize that non-enhanced CT (NECT) post-processing with frequency-selective non-linear blending (“best contrast”/BC) increases its accuracy in detecting edema and irreversible tissue damage (infarction).MethodsWe retrospectively analyzed the NECT scans of 76 consecutive patients with ischemic stroke (exclusively middle cerebral artery territory—MCA) before and after post-processing with BC both at baseline before reperfusion therapy and at follow-up (5.73±12.74 days after stroke onset) using the Alberta Stroke Program Early CT Score (ASPECTS). We assessed the differences in ASPECTS between unprocessed and post-processed images and calculated sensitivity, specificity, and predictive values of baseline NECT using follow-up CT serving as reference standard for brain infarction.ResultsNECT detected brain tissue hypoattenuation in 35 of 76 patients (46.1%). This number increased to 71 patients (93.4%) after post-processing with BC. Follow-up NECT confirmed brain infarctions in 65 patients (85.5%; p = 0.012). Post-processing increased the sensitivity of NECT for brain infarction from 35/65 (54%) to 65/65 (100%), decreased its specificity from 11/11 (100%) to 7/11 (64%), its positive predictive value (PPV) from 35/35 (100%) to 65/69 (94%) and increased its accuracy 46/76 (61%) to 72/76 (95%).ConclusionsThis post-hoc analysis suggests that post-processing of NECT with BC may increase its sensitivity for ischemic brain damage significantly.

Frequency-selective non-linear blending for the computed tomography diagnosis of acute gangrenous cholecystitis: Pilot retrospective evaluation

“…between l 1 [-20 HU] and l 2 [100 HU]) range of Hounsfield unit values generating images with up to 300% improved tissue contrast [ 18 ]. The suitable parameter settings we established for diagnosing GC and AC with this application (centre of 30 HU, delta of 5 HU at a slope of 5) significantly differed from previous clinical applications focusing on other pathologies [ [15] , [16] , [17] , 24 ]. The five adjustable parameter settings we are proposing in this report proved generally adequate in our cohort.…”

“…For the frequency-selective non-linear blending reading session, all CT images – performed in daily routine with a soft tissue kernel B30 and filtered back projection reconstruction with conventional linear weighting of frequencies – were transferred to an external offline workstation with a frequency-selective non-linear blending prototype software (Siemens Healthineers) [ [15] , [16] , [17] , [18] ]. The algorithm enabling non-linear blending of CT images first divided image information into low and high frequencies, whereas high frequencies represented the main part of image noise and low frequencies included contrast information.…”

“…Contrary to linear blending, which affects the entire dynamic contrast range, frequency-selective non-linear blending can be applied to a select range of Hounsfield units, e.g. in the low-keV range to improve the visibility of possibly undetectable small differences in tissue contrast [ [15] , [16] , [17] , [18] ]. Frequency-selective non-linear blending is independent of the acquisition technique and can be applied to single and dual energy CT data.…”

Improved CT-detection of acute bowel ischemia using frequency selective non-linear image blending

“…The F-NLB post-processing algorithm has been described in previous studies ( 8 – 10 ). F-NLB images were computed using a new algorithm enabling non-linear blending in image space.…”

Using Correlative Properties of Neighboring Pixels to Improve Gray-White Differentiation in Pediatric Head CT Images

“…1,2,[28][29][30][31] Using the same image-processing algorithm that improved GWD on head CT images with normal findings, previous investigators were able to improve the accuracies of radiologists in diagnosing acute infarction and encephalitis on head CTs. 13,30,32 Further studies are needed to test whether improved gray-white differentiation afforded by CIE on head CT images can translate into similar improved sensitivity for the detection of disease processes such as ischemic infarcts (Fig 5).…”