CAD Performance Analysis for Pulmonary Nodule Detection: Comparison of Thick- and Thin-

Slice Helical CT Scans

Randy D Ernst1, Russell C Hardie2, Metin N Gurcan3, Aytekin Oto1,

Steve K Rogers3, Jeffrey W Hoffmeister3

1. Department of Radiology, The University of Texas Medical Branch, Galveston TX

2. iCAD Inc. and University of Dayton, Dayton OH 3. iCAD Inc., Beavercreek OH

Introduction

This study compares the performance of a CAD (QuickCue™, iCAD, Inc.) system in detecting lung nodules from thick- and thin-slice multi-detector row CT scans, and to evaluate the potential benefit of CAD on radiologist sensitivity.

Methods and Materials

57 reports reviewed retrospectively Case selection:Obtained during a 5-month periodReferred from multiple departmentsContain at least 1 pulmonary nodule but

fewer than 10 nodules to localizeHave no significant breathing miss -

registration, post surgical changes, pleural effusions & atelectasis

Methods and Materials

4-detector LightSpeed QX/I Scanner, GE systems

HQ setting with 5.0 collimation, helical pitch of 0.75/1.0

Standard-dose (160 - 270 mA, 120 kVp)

Images were reconstructed at 5 mm (thick) and 2.5 mm (thin) slice thicknesses.

Methods and Materials140 nodules (3 mm - 25 mm) were identified pre-CAD by radiologists From thick-slice cases only.

Cases with multiple nodules were excluded.Truth marks were mapped to the thin-slice dataMean nodule size 7.3 ± 4.2 mm (3 – 25 mm)Gold standard for nodule truth comes for post-CAD Radiologist review One gold standard for thick-slice and one for thin-

slice

CAD System (QuickCue™, iCAD Inc.)

3D LungSegmentation

3D CandidateSegmentation

CalculateFeatures

DICOMImages

Classifier

DetectionMask

CAD detected 72.1% (101/140) of the pre-CAD truth nodules

CAD detected 35 additional radiologist-confirmed nodules, an increase of 25% (35/140) in sensitivity

5.6 (317/57) false-positives per case55 due to atelectasis18 due to scarring

Review of Thick-Slice CAD Results

Venn Diagram for Thick

3

39 35

317

CADPre-CAD Review

Post-CAD ReviewGold Standard

101

0 0

CAD detected 80.7% (113/140) of the pre-CAD truth nodules.

CAD detected 94 additional radiologist-confirmed nodules, an increase of 67.1% (94/140).

4.6 (262/57) false-positives per case.70 due to atelectasis39 due to scarring

Review of Thin-Slice CAD Results

Venn Diagram for Thin

0

26 94

262

CAD using thin-slice

Pre-CAD Review using thick-slice with detections mapped to thin-slice

Post-CAD Review of thin-sliceGold Standard

113

0 0

ComparisonThick-slice cases

Thin-slice cases

CAD sensitivity

72.1% 80.7%

Radiologist sensitivity increase after CAD

+25% +67.1%

FPs 5.6 4.6

FROC Curve for CAD

0 2 4 6 8 10 12 140

0.2

0.4

0.6

0.8

1

Average False Positives Per Case

Pro

bab

ility

of

Det

ecti

on

Thin SliceThick Slice

CAD detections in Thick-Slice

0 5 10 15 20 250

5

10

15

20

25

30

35

Size (mm)

Nu

mb

er

of

No

du

les

Radiologist DetectedRadiologist MissedAdditional Detections

CAD detections in Thin-Slice

0 5 10 15 20 250

10

20

30

40

50

Size (mm)

Nu

mb

er

of

No

du

les Radiologist Detected

Radiologist MissedAdditional Detections

5 primary lung cancers

24 cases of metastatic cancer including 7 lymphomas, 4 breast, 4 head and neck, 2

colon, 2 pancreas, 1 carcinoid, 1 seminoma,  1 ovarian, 1 melanoma and 1 tracheal papillomatosis

23 cases of infection, including19 granulomatous disease either calcified,

stable on follow-up or biopsy proven. 4 were presumed infection that resolved with follow-up

1 case proved to be a thrombosed AVM

4 cases lost to follow up

Case Follow-up

Example TPs

Examples of nodules that are detected by both radiologist and CAD

Example TPs

Examples of nodules that are initially missed by radiologists then detected after reviewing CAD

Review of CAD ResultsSources of false positivesVessel intersections Inaccurate lung segmentationPartial volume effectsOther lung abnormalities (scarring,

atelectasis)

Example FPs

Review of CAD ResultsSources of false negatives (missed nodules)Low density, irregularStrong connectivity with vessels Imperfect candidate segmentation Inaccurate lung segmentation

Example FNs

Conclusions

Preliminary results indicate that both sensitivity and specificity of the CAD system increases when used with thin-slice scans versus thick-slice scans.The CAD system operating on both thick- and thin-slice scans improved radiologist sensitivity Improvement was greater for CAD

operating on thin-slice scans