QIBA CT Volumetrics - Cross-Platform Study (Group 1C) March 18, 2009 Interclinic Comparison of CT Volumetry Quantitative Imaging Biomarker Alliance

Charge 1. To agree on the scanner settings and other protocol elements under which imagery is to be collected. 2. To agree on requirements of phantoms to be imaged/measured. 3. To agree on the platforms and centers to be selected under which imagery is to be collected. 4. To identify the measurements and the algorithms for use in image processing. 5. To specify the analysis of the measurements.

Goals 1. Measure the volume of nodules on CT imagery collected from several CT scanners and sites (includes single scanners with varying settings). 1. Measure image noise and determine its impact on the measurement of volume. 2. Compare the accuracy and precision of volume measurements for these phantom datasets. 3. Determine the minimum detectable level of change that can be achieved when measuring nodules in phantom datasets.

Goal 1 1.Measure nodule volume on CT imagery collected from several CT scanners/sites (including single scanners with varying settings). Determine the systems to be used and the system settings to be varied. (a) kVp constant. (b) mAs constant. (c) collimation fixed (+) (d) field of view ([rib-to-rib]skin-to-skin = closest possible view)- (e) reconstruction filters – follow-up Wendy & radiologists -Find “equivalent” filters. Site selection – poll the team. Scanners follow sites.

Goal 2 2. Measure “image noise” and determine its impact on the measurement of volume. Facilitates inter-comparison of scanner results. (a) Characterizing / specifying image quality (a) Expert visual assessment of image quality. (Deni)

QIBA – What to do? Experiments Investigate parameter space to determine which parameters make a difference in the task (CT tumor volume and volume measurement over time) QIBA CT 1-A and 1-B already contribute to this investigation? NOTE: Different biomarkers (e.g. lesion density or mass) may be affected by different parameters.

QIBA CT 1-C Profiles - 1 As with NLST and ACRIN 6678, we could specify kVp, slice thickness, mAs, rotation time, pitch, reconstruction kernel (affects MTF) (NOTE: These operating parameters serve as a proxy for physical performance with respect to spatial resolution, noise and dose.)

QIBA CT 1-C Profiles - 2 ALTERNATIVE (not necessarily exclusive OR): Specify PERFORMANCE metrics such as simple spatial resolution and noise metrics.  kVp (affects contrast difference between materials)  Slice thickness, recon interval (affects z-axis resolution & noise)  Rotation time and pitch (coverage, breath hold, etc.)  Recon kernel OR recon kernel performance –e.g. Choose kernel such that you can see 6 or 7 (but no more than 7) lp/cm on ACR phantom….or –10% MTF should be between 6 and 7 lp/cm  mA/effective mAs level OR mA level performance –e.g. Choose 40 effective mAs OR –Choose effective mAs level so that std dev is between 20 and 30 HU in 20 cm water phantom

QIBA – What to do?  Near Future: –Specify  MTF  NPS  Z-axis resolution  Dose  Some SNR metric appropriate for measurement task  Further: –Specify  3D MTF  3D NPS  Organ dose  Some SNR/Dose metric appropriate for measurement task/risk

Example Protocol Chart for NLST (from Cagnon et al) ParameterSiemens Vol Zoom/ Sensation 4 4-slice/0.5 sec 4 x 2.5 Siemens Vol Zoom/ Sensation 4 4-slice/0.5 sec 4 x 1 Siemens Sensation x.75 Siemens Sensation 64 64x.0.6 (beam collimation 32x0.6) kV120 Gantry Rotation Time0.5 sec 0.50 sec mA (Regular patient-Large patient values) mAs (Reg-Lg) Scanner effective mAs 2 (Reg-Lg) Detector Collimation (mm) - T2.5 mm1 mm0.75 mm0.6 mm Number of active channels - N Detector Configuration - N x T4 x 2.5 mm4 x 1 mm16 x.75 mm32 x 0.6 mm Collimation (on operator console)N/A 64x0.6mm Table incrementation (mm/rotation) - I15 mm8 mm18 mm19.2 mm Pitch ([mm/rotation] /beam collimation) - I/NT Table Speed (mm/second)30 mm/sec16 mm/sec36 mm/sec38.4 mm/sec Scan Time (40 cm thorax) 13 sec25 sec11 sec Nominal Reconstructed Slice Width3 mm2 mm Reconstruction Interval mm1.8 mm Reconstruction Algorithm 3 B30 # Images/Data set (40 cm thorax) CTDI vol (Dose in mGy) – 4.1 mGy mGy mGy

Goal 3 Compare the accuracy and precision of measurements for these phantom datasets. Which measurements: image mask? Volume? RECIST? (a) RECIST vs. volume (b) Investigate variance & bias. (c) Inter-system variation. (d) Intra-system variation.

Goal 4 4. DEFER: Determine the minimum detectable level of change that can be achieved when measuring nodules in phantom datasets.

Existing Resources  RadPharm –What mark-up is recommended? What format?  RECIST  Segmentation mask. Formats?

Next Steps  Continue to Refine Questions and Experimental Design (similar to 1A and 1B)  Recruit participating clinics. Share and discuss plan with associated medical physicists.