Neuro Best Contrast Filter for Head CT XIX Symposium Neuroradiologicum Evaluation of Neuro Best Contrast Filter for Head CT Z. Rumboldt, S. Tipnis, D. Vincent, M.V. Spampinato, G. Goldsberry, W. Huda Medical University of South Carolina Charleston, SC, USA

Background CT images traditionally reconstructed using filtered back projection techniques (FBP) FBP limitations: geometry, data completeness, radiation dose Increased spatial resolution is directly correlated with increased image noise

Facts Analysis Diagnostic value of CT images is limited by the available contrast-to-noise ratio (CNR) CNR is small particularly for soft tissue (with low contrast) CNR improvement by higher dose is undesirable Analysis Image noise is dominated by high spatial frequencies Soft tissue representation (low contrast detectability) mainly depends on medium/low frequencies  Image enhancement by frequency band-selective processing

noise divided by contrast spatial frequency noise divided by contrast high freq. band low freq. band details with high contrast (vessels, bone, …) soft tissue contrast

Decomposition into Frequency Bands high pass sharp details and major part of noise complementary filters low pass smooth content, but little noise

Multiband Image Enhancement (MBE) I small details high pass complementary filters + low pass non-linear look-up original image enhanced image contrast enhancement without substantial increase of noise

original image NBC image

MBE improves CNR of specific image features Head: gray/white matter differentiation (CNR gain up to ~40%) CNR improvement can be translated into radiation dose reduction 30% less dose demonstrated in example realistic in general: 20% (further clinical studies needed)

Background

Purpose NBC Evaluation in a Clinical Setting Novel Methodology for lesion detection Comparison with normal scans with the same filter, not the same scan with different filters side by side

Materials and Methods Part 1 5 consecutive Head CT scans with FBP 7 consecutive Head CT scans with NBC HU measurements – circular ROI Part 2 Novel Methodology for lesion detection

Materials and Methods Total screened 228 Age range selected 25 through 85 Both genders 24 abnormal subjects - 30 lesions: 21 hypointense 7 hyperintense 1 mixed 1 isointense 12 normal subjects selected to match

Materials and Methods In house software (MUSC, Matthew Daniels, website accessible on campus network) Displayed pairs of single slice CT - Abnormal on Left Location and description of lesion given Rating scale 1 to 10 1 = Barely discernable 10 = Definitely see lesion PATHOLOGY COMPARED TO THE NORMAL 3 sets for each pair: FBP, NBC, IRIS

Materials and Methods Analysis Ratios of obtained values: NBC/FBP Every reader trained on practice set prior to study Individual randomization for every reader Every reader trained on practice set prior to study Individual randomization for every reader Materials and Methods Every reader trained on practice set prior to study   Individual randomization for every reader Analysis Ratios of obtained values: NBC/FBP IRIS/FBP

Materials and Methods FBP IRIS NBC

Materials and Methods FBP

Materials and Methods IRIS

Materials and Methods NBC

Results FBP Part 1 CSF FAT BONE GM WM 39.83 32.30 42.71 34.62 40.49 10.72 -91.52 1166 39.83 32.30 11.7 -2.6 1158 42.71 34.62 10.14 -73.01 1124 40.49 32.41 8.511 -62.14 938 38.55 31.97 10.85 -98 734 39.68 33.37 8.45 -101 1005 37.28 32.73 6.68 -80.71 849.9 38.15 32.45 9.5787 -72.7114 996.4143 39.5271 32.8357 1.7583 33.8746 165.8116 1.7829 0.8987

Results NBC CSF FAT BONE GM WM 5.1 -107 901 37.00 26.00 4.3 -81.9 1009 37.42 26.62 0.05 -99.33 963.4 34.13 24.61 5.2 -84.98 917 38.46 30.80 4.9 -90.66 1019 36.90 27.80 2.8 -76 1219 37.40 24.11 1.53 -64.48 869 33.54 21.61 5.9 -82 763 37.69 26.48 3.77 -105 738.2 36.71 26.21

Results GM WM 39.53 32.84 FBP 36.58 26.03 NBC CSF FAT BONE 9.5787 -72.7114 996.4143 39.53 32.84 1.7583 33.8746 165.8116 1.7829 0.8987 FBP 3.7277 -87.9278 933.1778 36.58 26.03 1.8162 13.1863 136.6727 1.5522 2.3969 NBC

Results mean difference in HU between GM and WM: 6.69 with standard FBP 10.55 using NBC Avg. increase 3.86 HU NBC FBP

NBC/FBP lesion detection ratio Part 2 NBC/FBP lesion detection ratio AVG. HYPO RATIO 1.34 1.69 1.07 SD HYPO RATIO 0.77 2.13 0.43 AVG. HYPER RATIO 1.51 1.12 1.02 SD HYPER RATIO 0.72 0.48 0.18 AVG. RATIO 1.45 1.54 1.09 SD RATIO 0.82 1.82 0.41 Rater 1 Rater 2 Rater 3

Pooled Results – all 3 raters NBC/FBP Pooled Avg. Hypo 1.37 Pooled Std.Dev. Hypo 1.34 Pooled Avg. Hyper 1.22 Pooled Std.Dev. Hyper 0.53 Pooled Average 1.36 Pooled Std. Dev 1.18

Conclusion NBC filter provides increased contrast between GM and WM on Head CT scans, which seems to improve lesion detection Alternatively, it may allow for a decrease in radiation dose