Z. Rumboldt, S. Tipnis, D. Vicent,M.V. Spampinato, G. Goldsberry, W. Huda

Medical University of South CarolinaCharleston, SC, USA

XIX Symposium Neuroradiologicum

Iterative Reconstruction Algorithm for Head CT

BackgroundCT 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

BackgroundITERATIVE IMAGE RECONSTRUCTION approaches recently proposed and introducedmay allow for improved image quality and lower noise(2 Alternative Forced Choice methodology)

iterative reconstruction may allow decoupling

of spatial resolution and image noise

need for a substantial increase in computation power

compared to conventional FBP reconstruction

After an image is reconstructed, “reprojection” simulates the CT measurement process, with the image as the object, followed by corrections

Each time the image is updated, processing algorithmenhances spatial resolution at higher object contrasts & reduces image noise in low contrast areas

Purpose

Novel Methodology

Comparison with normal scans for lesion detection, not side by

side

Clinical evaluation of potential noise reduction andimproved lesion detection

Material and MethodsPart 1

10 adult head CTs – both FBP and IRIS

2 neuroradiologists evaluated simultaneously both sets for each patient at 3 levels - MCP, BG, and centrum semiovale (30 levels in all) for noise and artifacts

raters blinded for the algorithm had 3 choices: preference for A, for B, no preference

Materials and Methods

Total screened 228 Age range selected 25 through 8524 abnormal subjects - 30 lesions: 21 hypo 7 hyper 1 mixed 1 iso

12 normal subjects selected to match

Part 2

Materials and MethodsIn house software (MUSC, Matthew Daniels, website accessible on campus network)

Displayed pairs of single slice CT - Abnormal on LeftLocation and description of lesion givenRating 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

FBP NBCIRIS

FBP

IRIS

NBC

Every reader trained on practice set prior to study Individual randomization for every reader

AnalysisRatios of the obtained values: IRIS/FBP

NBC/FBP

Materials and MethodsEvery reader trained on practice set prior to studyIndividual randomization for every readerEvery reader trained on practice set prior to studyIndividual randomization for every reader

FBP IRIS

Results

Results

In all evaluated images (30 levels) noise was considered lower with IRIS compared to FBP

Artifacts were less prominent in 11 of the 30 evaluated levels using IRIS and in 3 using FBP (no preference was found for 16 levels)

Part 1

IRIS NBC

Results

Results

IRIS NBC

FBP (d) NBC (d') IRIS (d") d'/d d"/d1 3 1 3.00 1.001 3 3 3.00 3.008 7 7 0.88 0.886 3 2 0.50 0.336 2 5 0.33 0.834 7 6 1.75 1.509 6 7 0.67 0.786 7 3 1.17 0.503 3 5 1.00 1.673 3 5 1.00 1.671 2 4 2.00 4.006 7 3 1.17 0.503 4 5 1.33 1.677 1 5 0.14 0.714 7 7 1.75 1.757 5 9 0.71 1.293 5 7 1.67 2.338 8 8 1.00 1.002 4 6 2.00 3.004 4 7 1.00 1.752 4 2 2.00 1.002 7 8 3.50 4.004 6 7 1.50 1.753 8 6 2.67 2.003 7 8 2.33 2.677 6 10 0.86 1.435 5 3 1.00 0.603 4 7 1.33 2.338 7 10 0.88 1.254 6 4 1.50 1.00

Rater 1

Part 2

Rater 1 NBC/FBP IRIS/FBP

Avg. Hypo 1.34 1.48Std.Dev. Hypo 0.77 0.94

Avg. Hyper 1.51 1.61Std.Dev. Hyper 0.72 0.75

Average 1.45 1.61Std. Dev 0.82 0.97

Results

AVG. HYPO RATIO 1.34 1.48 1.69 1.49 1.07 1.22

SD HYPO RATIO 0.77 0.94 2.13 1.21 0.43 0.41

AVG. HYPER RATIO 1.51 1.61 1.12 1.18 1.02 1.05

SD HYPER RATIO 0.72 0.75 0.48 0.47 0.18 0.26

AVG. RATIO 1.45 1.61 1.54 1.42 1.09 1.24SD RATIO 0.82 0.97 1.82 1.04 0.41 0.45

NBC IRIS NBC IRIS NBC IRIS

Rater 1 Rater 2 Rater 3

Results Pooled Results NBC IRIS

Pooled Avg. Hypo 1.37 1.40Pooled Std.Dev. Hypo 1.34 0.91

Pooled Avg. Hyper 1.22 1.28Pooled Std.Dev. Hyper 0.53 0.56

Pooled Average 1.36 1.42Pooled Std. Dev 1.18 0.87

ConclusionIterative reconstruction algorithm decreases noise in Head CT images

It seems to improve lesion detection

It may allow decreased radiation dose

No clear difference between IRIS and NBC