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Goal

Physics Testing for Performance Based Protocol version 3.0 (Now based on ACRIN 6678) QIBA Group 1C. Goal. From a specification of image quality performance, determine scanner settings which achieve that performance. Statement of Image Quality Performance.

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Goal

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  1. Physics Testing for Performance Based Protocolversion 3.0(Now based on ACRIN 6678) QIBA Group 1C

  2. Goal From a specification of image quality performance, determine scanner settings which achieve that performance

  3. Statement of Image Quality Performance • QIBA 1C Image Quality Performance Specification: • 120 kVp • Reconstructed slice thickness between 0.75 to 1.25 mm • Beam Collimation (Detector configuration), Pitch and rotation time set to that scan through an entire thorax could be completed in under 15 seconds* • Spatial Resolution of 6 lp/cm on ACR phantom spatial resolution section in ACR Phantom Module 4 • Standard Deviation (proxy for noise) of 17±1 HU in ACR Phantom water equivalent Uniformity Module- Module 3 * Example of a breathold constraint; technically not an image quality performance specification, but related.

  4. General Outline of Testing Protocol • Record required data on accompanying spreadsheet, • Note that spreadsheet has two tabs to allow two Scan Field of View (or Patient Size) settings to be used if necessary. • If Scanner has multiple Patient size (Toshiba) or SFOV (GE) settings, then perform measurements twice, once each for: • SFOV or Patient Size that is appropriate for size of phantom (20 cm diameter) AND • SFOV or Patient Size that would be appropriate for adult thorax (approx. 35 cm diameter) • Set Scan Field of View or Patient Size (or equivalent). • Set 120 kVp • Set Slice thickness between 0.75 to 1.25 mm (depending on scanner’s available reconstructed slice thickness) • Set nominal beam collimation (NxT such as 16 x 0.5mm, or 128x0.6mm, 320 x 0.5 mm) rotation time and pitch such that scan can cover a 35 cm thorax in 15 seconds or less • Values near pitch 1 are preferred. • ITERATE (hopefully only a few times) on reconstruction kernels to meet spatial resolution spec. • ITERATE (again, hopefully just a few times) on mAs or effective mAs setting, given beam collimation, pitch and rotation time.

  5. Specific Instructions for Testing Protocol • On accompanying spreadsheet, record: • Scanner Manufacturer (e.g GE) • Model (e.g. VCT) • Site id (e.g Scanner 95) • Software version • Testing date (12-26-09) • Set kVp to 120 or just lower if there is no 120 kVp setting • Record selected setting on accompanying spreadsheet • If Scanner has multiple Patient size (Toshiba) or SFOV (GE) settings, then perform measurements twice, once each for: • SFOV or Patient Size appropriate for phantom size (20 cm diameter) AND • SFOV or Patient Size appropriate for adult thorax (approx. 35 cm diam) • Record selected setting on accompanying spreadsheet • Use different tabs for each set of measurements • Set reconstructed slice thickness between 0.75 to 1.25 mm (depending on scanner’s available reconstructed slice thickness) • Record selected setting on accompanying spreadsheet

  6. Specific Instructions for Testing Protocol • Set the following parameters such that the scan could cover a 35 cm thorax in ≤ 15s AND that reconstructed slice thickness selected in step 4 is possible. The accompanying spreadsheet calculates scan time for 35 cm long thorax given selected parameters Select: • Nominal beam collimation (NxT such as 16 x 0.5mm, or 64x0.625mm, 320 x 0.5 mm, etc.) • Rotation time (in seconds) • Pitch (Values near pitch 1 are preferred)

  7. Specific Instructions for Testing Protocol • ITERATE on recon kernels to get 6 lp/cm in ACR phantom 6.1 Scan phantom once through section 4 of ACR CT accreditation phantom, using: • kVp selected in step 2 • Patient size or SFOV selected in step 3 • Reconstructed slice thickness selected in step 4 (use contiguous reconstructions) • Other acquisition parameters (nominal beam collimation, rotation time, pitch) as selected in step 5. • Select mA, mAs/rotation or effective mAs – for this step, use high enough mA to get 200 effective mAs; spreadsheet has calculator to confirm 200 effective mAs (even if you specify mA). • Record mA or mAs or eff. mAs setting on spreadsheet. • Instructions continued on next page

  8. Specific Instructions for Testing Protocol 6.2Reconstruct images using several recon kernels, display with Level =1100, Window=100 • For each recon filter used: • Record the name of recon filter • Record the size of the line pair object (e.g. 6 lp/cm etc.) observed for that filter • Select smoothest kernel that allows user to see 6 lp/cm: • Record the name of recon filter selected • Provideimage (DICOM AND jpeg) reconstructed with this filter Zoomed in Zoomed in B30 B45 6 lp/cm 6 lp/cm 7 lp/cm 7 lp/cm ACR Spatial Resolution Section (Module 4)

  9. Specific Instructions for Testing Protocol 7 ITERATE on mA or eff. mAs settings to meet Standard Deviation Specification (17±1 HU) 7.1 Scan and reconstruct images of section 3 (homogeneity) of ACR CT accreditation phantom, using: • kVp selected in step 2 • Patient size or SFOV selected in step 3 • Reconstructed slice thickness selected in step 4 (use contiguous reconstructions) • Other acquisition parameters (nominal beam collimation, rotation time, pitch) as selected in step 5. • Reconstruction filter as selected in Step 6 • Select an initial mA (or mAs or effective mAs) setting • Record initial mA or eff. mAs setting on spreadsheet • From Reconstructed image, measure standard deviation by placing an ROI of approximately 400 mm2 at the center of the image • Record standard deviation for this setting on spreadsheet

  10. Specific Instructions for Testing Protocol 7.2 If standard deviation is within specification (17±1 HU), then: • Record mA (or eff. mAs setting) • Record scanner reported CTDIvol • Provideimage (DICOM AND jpeg) using this setting. 7.3 If standard deviation is NOT within specification (17±1 HU), then: • Adjust mA (or eff. mAs) setting and repeat steps 7.1.f and 7.1.g until standard deviation is within specification. • When specification is met, then perform step 7.2

  11. Example of Testing Protocol to Determine Parameters That Meet Specification • Step 7 – Example on Siemens Sensation 64. • 100 eff. mAs • Tech. Params: • 120 kVp • 1mm • Pitch 1 • 0.5 sec • B30 Spec: std dev= 17±1 HU MEETS SPEC! 100 eff. mAs; std dev = 17

  12. Testing Protocol to Determine Parameters That Meet Specification • Conclusion: For Siemens Sensation 64, these settings meet QIBA 1C specifications: • 120 kVp • Reconstructed Slice thickness 1.0 mm • Nominal beam collimation 64x0.6 (actually 32x0.6 with flying focal spot) • Rotation time 0.5 seconds • Pitch 1.0 • Recon kernel B30 • Effective mAs setting 100 • CTDIvol = 7.7 mGy

  13. For Scanners with Multiple Patient Size (Toshiba) or SFOV (GE) Settings • Repeat Steps 1-7 for 2nd patient size setting • Record results on second tab of spreadsheet

  14. Next Scanner?

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