Quality Control Concerns for New Generations of CT, MRI, & PET

David W. Jordan, Ph.D.Sr. Medical Physicist , UH Case Medical Center

Clinical Assistant Professor, CWRU

Disclosures

• No financial disclosures or industry relationships

• Member of organizations discussed:– AAPM TG-126 (PET)– AAPM WGMRQA (MRI)

Objectives

• Understand the typical elements of a QC program for CT, MRI, and PET equipment.

• Anticipate the QC challenges created by new imaging technology advances.

Outline

• Overview of current QC procedures for CT, MRI, and PET.

• Discuss new CT technology : wide/cone beams and iterative reconstruction

• Discuss new MRI technology: parallel imaging and massively multichannel coils

• Discuss new PET technology: time of flight and alternatives to PMT detectors

QC Perspectives

• Medical Physicist

• Imaging Technologist

QC Goals

• Obtain data to characterize performance (and dose)

• Obtain data to optimize performance• Monitor constancy of function/performance

“Meta” QC:What is the Quality of your Quality Control?

• Does each test contribute to– characterization, and/or– optimization, and/or– constancy?

“Meta” QC:What is the Quality of your Quality Control?

• Is each test:– Clinically relevant?– Feasible? (time, cost)– Sensitive?– Specific?

“Meta” QC:What is the Quality of your Quality Control?

• Is each/every test mandated by:– ACR?– AAPM TG # such and such?– Joint Commission?– ACRIN / CRO?– Ohio Department of Health?– Etc.?

CT

Current QC: CT

• QC phantom measurements:– CT # accuracy/linearity– Uniformity– Noise / CNR / SNR– High & low contrast– Scanner alignment

Current QC: CT

• Dose: CTDI100

• 16 & 32 cm dia. cylinders (10-15 cm thick)

• Measure scanner output

CT Advances: Iterative Recon

M.J. Willemink et al., “Iterative reconstruction techniques for computed tomography Part 1: technical principles.,” Eur. Radiol. 23(6), 1623–31 (2013).

CT IR QC Challenges

• IR techniques manipulate image noise

• Radiologists report “texture” concerns with reconstructed images

• Details of reconstruction proprietary– Is CT # manipulated / better / worse?

CT IR QC: What and How To Test?

• Characterization?• Optimization?• Constancy?

• Clinically relevant?• Feasible?• Sensitive?• Specific?

CT Advances: Wide Beams

© Xoran Technologies, http://xorantech.com/minicat-technical-specifications/

© Toshiba Medical Systems, http://www.toshiba-medical.eu/upload/TMSE_CT/Aquilion_QDE_L.jpg?epslanguage=en

100-mm CTDI “pencil” chamber

Wide Beam QC Challenges• CTDI100 inadequate for dose (scanner

output) measurements• Proposed alternatives (TG-111)

cumbersome:– Large/long phantom– Non-standard equipment & metrics

• TG 200 working on feasibleimplementation

C. Descamps, M. Gonzalez, E. Garrigo, A. Germanier, and D. Venencia, “Measurements of the dose delivered during CT exams using AAPM Task Group Report No. 111.,” J. Appl. Clin. Med. Phys. 13(6), 3934 (2012).

Wide/Cone Beam CT Dose: How To Test?

• Characterization?• Optimization?• Constancy?

• Clinically relevant?• Feasible?• Sensitive?• Specific?

CT Coming Attractions…

• CT performance assessment including iterative reconstructions:– AAPM Task Group

223– Established 2012– Ehsan Samei, Chair

• Development of wide/cone beam dosimetry:– AAPM Task Group

200– Established 2010– Donovan Bakalyar,

Chair

MRI

Current QC: MRI• Magnet homogeneity• Scanner performance

– Slice position/thickness

– Geometric accuracy– Resolution– Artifacts

• Performance of all individual coils– SNR, uniformity

MRI Advances: Parallel Imaging

R. Hashemi, W.G. Bradley, and C.J. Lisanti, MRI: The Basics (Lippincott Williams & Wilkins, 2010).

Parallel MRI QC Challenges

Parallel MRI: What/How To Test?

• Characterization?• Optimization?• Constancy?

• Clinically relevant?• Feasible?• Sensitive?• Specific?

MRI Advances: Coils

T. Niendorf et al., “Progress and promises of human cardiac magnetic resonance at ultrahigh fields: a physics perspective.,” J. Magn. Reson. 229, 208–22 (2013).

Coil QC Challenges

• State of the art coil arrays have up to 128 channels– Many MORE individual elements in some

arrays!• Existing methods:

– Simple/aggregated scan may miss problems– Thorough testing can take hours per coil,

typical scanner has 10-20 coils

MRI Coil Arrays: What/How To Test?

• Characterization?• Optimization?• Constancy?

• Clinically relevant?• Feasible?• Sensitive?• Specific?

MRI Coming Attractions…

• Parallel Imaging Technology & QC:– AAPM Task Group

118– Established 2005– Nathan Yanasak,

Chair

• RF Coil QC (and other topics):– AAPM WG on MR

Testing and QA– Established 2005– Joseph Och, Chair

PET

Current QC: PET• Phantom images

– SUV accuracy– Contrast cold/ ”warm”

/hot objects– “Resolution”

• Count rate response vs. activity

• Sensitivity• Spatial resolution• Corrections

PET Advances: Time of Flight

• Diagram of line of response vs “segment”of response

TOF-PET: What/How To Test?

• Characterization?• Optimization?• Constancy?

• Clinically relevant?• Feasible?• Sensitive?• Specific?

PET Advances: New Detectors

http://staff.science.uva.nl/~zoon/sms/SMS.html

Non-PMT Detector QC Challenges

• Air-cooled arrays’ performance depends on ambient temperature

• Detection efficiency and speed affect sensitivity, count rate performance

• Enable or require use of different scintillators?

• Effect of timing resolution?

Post-PMT PET: What/How To Test?

• Characterization?• Optimization?• Constancy?

• Clinically relevant?• Feasible?• Sensitive?• Specific?

PET Coming Attractions…

• PET-CT Acceptance Testing & QC:– AAPM Task Group

126– Established 2005– Osama Mawlawi,

Chair

Review of Objectives

• New technology developments:– CT: iterative recon, wide beams, dose

reduction technology– MRI: parallel imaging and multichannel coils– PET: time of flight and non-PMT detectors

• New technologies may or may not be adequately addressed by existing QC methods

Thank you!

• Questions?