11

Physics Testing for Physics Testing for Performance Based ProtocolPerformance Based Protocol

version 2.2 version 2.2

QIBA Group 1CQIBA Group 1C

GoalGoal

From a specification of image quality From a specification of image quality performance,performance,

determine scanner settings which achieve that determine scanner settings which achieve that performanceperformance

Statement of Image Quality Statement of Image Quality PerformancePerformance

QIBA 1C Image Quality Performance QIBA 1C Image Quality Performance Specification:Specification: 120 kVp120 kVp Reconstructed slice thickness between 0.75 to 1.25 mmReconstructed slice thickness between 0.75 to 1.25 mm Beam Collimation (Detector configuration), Pitch and Beam Collimation (Detector configuration), Pitch and

rotation time set to that scan through an entire thorax rotation time set to that scan through an entire thorax could be completed in under 15 seconds*could be completed in under 15 seconds*

Spatial Resolution of 7 lp/cm on ACR phantom spatial Spatial Resolution of 7 lp/cm on ACR phantom spatial resolution section in ACR Phantom Module 4resolution section in ACR Phantom Module 4

Standard Deviation (proxy for noise) of 13Standard Deviation (proxy for noise) of 13±1±1 HU in ACR HU in ACR Phantom water equivalent Uniformity Module- Module 3Phantom water equivalent Uniformity Module- Module 3

* Example of a breathold constraint; technically not an image quality * Example of a breathold constraint; technically not an image quality performance specification, but related.performance specification, but related.

General OutlineGeneral Outline of Testing of Testing ProtocolProtocol

Record required data on accompanying spreadsheet, Record required data on accompanying spreadsheet, SetSet 120 kVp 120 kVp SetSet Scan Field of View or Patient Size (or equivalent) Scan Field of View or Patient Size (or equivalent)

setting to values that are appropriate for phantom being setting to values that are appropriate for phantom being scanned.scanned.

Set Set Slice thickness between 0.75 to 1.25 mm (depending Slice thickness between 0.75 to 1.25 mm (depending on scanner’s available reconstructed slice thickness)on scanner’s available reconstructed slice thickness)

SetSet nominal beam collimation (NxT such as 16 x 0.5mm, nominal beam collimation (NxT such as 16 x 0.5mm, or 128x0.6mm, 320 x 0.5 mm) rotation time and pitch such 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 lessthat scan can cover a 35 cm thorax in 15 seconds or less

Values near pitch 1 are preferred. Values near pitch 1 are preferred. ITERATEITERATE (hopefully only a few times) on reconstruction (hopefully only a few times) on reconstruction

kernels to meet spatial resolution spec.kernels to meet spatial resolution spec. ITERATEITERATE (again, hopefully just a few times) on mAs or (again, hopefully just a few times) on mAs or

effective mAs setting, given beam collimation, pitch and effective mAs setting, given beam collimation, pitch and rotation time.rotation time.

1.1. On accompanying spreadsheet, record:On accompanying spreadsheet, record:a)a) Scanner Manufacturer (e.g GE)Scanner Manufacturer (e.g GE)b)b) Model (e.g. VCT)Model (e.g. VCT)c)c) Site id (e.g Scanner 95)Site id (e.g Scanner 95)d)d) Software versionSoftware versione)e) Testing date (12-26-09)Testing date (12-26-09)

2.2. SetSet kVp to 120 or just lower if there is no 120 kVp setting kVp to 120 or just lower if there is no 120 kVp settinga)a) Record selected setting on accompanying spreadsheetRecord selected setting on accompanying spreadsheet

3.3. SelectSelect Patient Size (Toshiba), Scan Field of View (SFOV – Patient Size (Toshiba), Scan Field of View (SFOV – GE) or equivalent for each scanner. The value selected GE) or equivalent for each scanner. The value selected should be appropriate for size of phantom being scanned should be appropriate for size of phantom being scanned (ACR Phantom is 20 cm in diameter); do not use setting (ACR Phantom is 20 cm in diameter); do not use setting for adult thorax.for adult thorax.

a)a) Record selected setting on accompanying spreadsheetRecord selected setting on accompanying spreadsheet

4.4. Set Set reconstructed slice thickness between 0.75 to 1.25 reconstructed slice thickness between 0.75 to 1.25 mm (depending on scanner’s available reconstructed mm (depending on scanner’s available reconstructed slice thickness)slice thickness)

1.1. Record selected setting on accompanying spreadsheetRecord selected setting on accompanying spreadsheet

Specific Instructions forSpecific Instructions for Testing Testing ProtocolProtocol

5.5. SetSet the following parameters such that the following parameters such that the scan could cover a 35 cm thorax in the scan could cover a 35 cm thorax in ≤≤ 15s AND that reconstructed slice 15s AND that reconstructed slice thickness selected in step 4 is possible. thickness selected in step 4 is possible. The accompanying spreadsheet The accompanying spreadsheet calculates scan time for 35 cm long calculates scan time for 35 cm long thorax given selected parametersthorax given selected parameters

SelectSelect::a)a) Nominal beam collimation (NxT such as 16 Nominal beam collimation (NxT such as 16

x 0.5mm, or 64x0.625mm, 320 x 0.5 mm, x 0.5mm, or 64x0.625mm, 320 x 0.5 mm, etc.)etc.)

b)b) Rotation time (in seconds)Rotation time (in seconds)

c)c) Pitch (Values near pitch 1 are preferred)Pitch (Values near pitch 1 are preferred)

Specific Instructions forSpecific Instructions for Testing Testing ProtocolProtocol

6.6. ITERATEITERATE on recon kernels to get 7 lp/cm in ACR on recon kernels to get 7 lp/cm in ACR phantomphantom

6.1 Scan phantom6.1 Scan phantom once through section 4 of ACR CT once through section 4 of ACR CT accreditation phantom, using:accreditation phantom, using:a)a) kVp selected in step 2kVp selected in step 2

b)b) Patient size or SFOV selected in step 3Patient size or SFOV selected in step 3

c)c) Reconstructed slice thickness selected in step 4 (use Reconstructed slice thickness selected in step 4 (use contiguous reconstructions)contiguous reconstructions)

d)d) Other acquisition parameters (nominal beam collimation, Other acquisition parameters (nominal beam collimation, rotation time, pitch) as selected in step 5.rotation time, pitch) as selected in step 5.

e)e) SelectSelect mA, mAs/rotation or effective mAs – for this step, mA, mAs/rotation or effective mAs – for this step, use high enough mA to get 200 effective mAs; use high enough mA to get 200 effective mAs; spreadsheet has calculator to confirm 200 effective mAs spreadsheet has calculator to confirm 200 effective mAs (even if you specify mA). (even if you specify mA).

a)a) Record mA or mAs or eff. mAs setting on spreadsheet.Record mA or mAs or eff. mAs setting on spreadsheet.

f)f) Instructions continued on next pageInstructions continued on next page

Specific Instructions forSpecific Instructions for Testing Testing ProtocolProtocol

6.26.2 Reconstruct images Reconstruct images using several recon kernels, using several recon kernels, display with Level =1100, Window=100display with Level =1100, Window=100

a)a) For each recon filter used:For each recon filter used:a)a) Record Record the name of recon filterthe name of recon filterb)b) Record Record the size of the line pair object (e.g. 6 lp/cm etc.) the size of the line pair object (e.g. 6 lp/cm etc.)

observed for that filterobserved for that filterb)b) SelectSelect smoothest kernel that allows user to see 7 smoothest kernel that allows user to see 7

lp/cm:lp/cm:a)a) Record the name of recon filter selectedRecord the name of recon filter selectedb)b) ProvideProvide imageimage (DICOM or jpeg) reconstructed with this filter (DICOM or jpeg) reconstructed with this filter

6 lp/cm

7 lp/cm

6 lp/cm

7 lp/cm

B30 B45

ACR Spatial Resolution Section (Module 4)

Zoomed inZoomed in

Specific InstructionsSpecific Instructions for for Testing Testing ProtocolProtocol

7 ITERATE7 ITERATE on mA or eff. mAs settings to meet Standard on mA or eff. mAs settings to meet Standard Deviation Specification (Deviation Specification (1313±1±1 HU) HU)

7.1 Scan and reconstruct images of 7.1 Scan and reconstruct images of section 3 section 3 (homogeneity) of ACR CT accreditation phantom, (homogeneity) of ACR CT accreditation phantom, using:using:

a)a) kVp selected in step 2kVp selected in step 2b)b) Patient size or SFOV selected in step 3Patient size or SFOV selected in step 3c)c) Reconstructed slice thickness selected in step 4 (use Reconstructed slice thickness selected in step 4 (use

contiguous reconstructions)contiguous reconstructions)d)d) Other acquisition parameters (nominal beam collimation, Other acquisition parameters (nominal beam collimation,

rotation time, pitch) as selected in step 5.rotation time, pitch) as selected in step 5.e)e) Reconstruction filter as selected in Step 6Reconstruction filter as selected in Step 6f)f) Select an initial mA (or mAs or effective mAs) settingSelect an initial mA (or mAs or effective mAs) setting

a)a) Record initial mA or eff. mAs setting on spreadsheetRecord initial mA or eff. mAs setting on spreadsheet

g)g) From Reconstructed image, measure standard deviationFrom Reconstructed image, measure standard deviationa)a) Record standard deviation for this setting on spreadsheetRecord standard deviation for this setting on spreadsheet

Specific InstructionsSpecific Instructions for for Testing Testing ProtocolProtocol

7.2 7.2 If standard deviation is within specification (If standard deviation is within specification (1313±1±1 HU), then:HU), then:

a)a) RecordRecord mA (or eff. mAs setting) mA (or eff. mAs setting)

b)b) RecordRecord scanner reported CTDIvol scanner reported CTDIvol

c)c) ProvideProvide imageimage (DICOM or jpeg) using this setting. (DICOM or jpeg) using this setting.

7.3 7.3 If standard deviation is NOT within specification If standard deviation is NOT within specification ((1313±1±1 HU), then: HU), then:

a)a) Adjust mA (or eff. mAs) setting and repeat steps 7.1.f Adjust mA (or eff. mAs) setting and repeat steps 7.1.f and 7.1.g until standard deviation is within specification. and 7.1.g until standard deviation is within specification.

b)b) When specification is met, then perform step 7.2When specification is met, then perform step 7.2

Specific InstructionsSpecific Instructions for for Testing Testing ProtocolProtocol

Example of Testing Protocol to Example of Testing Protocol to Determine Parameters That Meet Determine Parameters That Meet

SpecificationSpecification Step 7 – Example on Siemens Sensation 64Step 7 – Example on Siemens Sensation 64..

Low Dose (25 eff. mAs)Low Dose (25 eff. mAs) Conventional Dose (250 eff. mAs)Conventional Dose (250 eff. mAs)

25 eff. mAs; std dev = 60 250 eff. mAs; std dev = 12.2

Spec: std dev= 12±1±1 HU

MEETSSPEC!

Tech. Params:•120 kVp•1mm•Pitch 1•0.5 sec•B45

Testing Protocol to Determine Testing Protocol to Determine Parameters That Meet Parameters That Meet

SpecificationSpecification Conclusion: For Siemens Sensation 64, these Conclusion: For Siemens Sensation 64, these

settings meet QIBA 1C specifications:settings meet QIBA 1C specifications: 120 kVp120 kVp Reconstructed Slice thickness 1.0 mmReconstructed Slice thickness 1.0 mm Nominal beam collimation 64x0.6 (actually Nominal beam collimation 64x0.6 (actually

32x0.6 with flying focal spot)32x0.6 with flying focal spot) Rotation time 0.5 secondsRotation time 0.5 seconds Pitch 1.0Pitch 1.0 Recon kernel B40Recon kernel B40 Effective mAs setting 250Effective mAs setting 250 CTDIvol = 19.2 mGyCTDIvol = 19.2 mGy

Next Scanner?Next Scanner?