Pivotal role of the medical physicist in diagnostic imaging:

the new challenges of hybrid imaging technology

Habib Zaidi1,2

1Geneva University Hospital, Geneva, Switzerland2Groningen University, Groningen, The Nethelands

Email: habib.zaidi@hcuge.ch

Web: http://pinlab.hcuge.ch

Second Global Forum on Medical Devices

Geneva, 22-24 November 2013

A qualified medical physicist is an individual who is competent to

practice independently one or more of the subfields of medical physics (see for e.g. IOMP/EFOMP recommendations)

Medical physics in clinical and research environments

Medical physicists are generally involved in four areas of activities:

Usually a medical physicist is involved in all four areas; the relative

distribution of responsibilities, however, varies considerably from one physicist to another, depending on the particular situation of the

employer as well as on the educational background and interest of

the physicist.

� clinical service and consultation;

� research and development; � teaching, and

� Administration

Convergence of multiple image-capture techniques, basic cell/molecular

biology, chemistry, medicine, pharmacology, medical physics,

biomathematics, and bioinformatics into a new imaging paradigm

Anatomic Physiologic Metabolic Molecular

PET/SPECT

x-ray CT

MRI

ultrasound

optical imaging

Molecular Imaging: Interdisciplinary!

Multimodality Imaging

Showing images on the iPod photo

Navigating beyond the 5th dimension …

From PET PET/CT PET/MR

PET PET/CT PET/MRI

Clinical adoption of PET-CT: a success story!

I. M. I. Division, PET market summary report, Tech. Rep. (2011)

The history of medicine has been defined by advances born of bioscience.But never before has it been driven to this degree by technology.

Hricak H, MSKCC (2013)

Scout Spiral CT PET PET/CT

0.2 - 0.8 mSv

Diagnostic CT (D-CT): 5 - 30 mSv

Low-Dose CT (LD-CT): 0.5 - 3 mSv

5-7 mSv

Average total dose: 25 mSv

Effective PET-FDG dose: Eint = ΓΓΓΓFDG x A, where ΓΓΓΓFDG = 19 µµµµSv/MBqEffective CT dose: Eext = ΓΓΓΓCT x CTDIvol, where ΓΓΓΓCT = 1.47 mSv/mGy

PET + LD-CT + D-CT: 10.7 - 40.8 mSv

PET + LD-CT: 5.7 - 10.8 mSv

PET + D-CT: 10.2 - 37.8 mSv

PET-CT: radiation dosimetry issues

2010: CT dose 2050 × mentioned in English language media

Concerns about CT radiation dose

Reducing CT radiation dose

imagegently.org imagewisely.org

Post-processing (adaptive filtering)

Baum et al. (2003) Eur Radiol

Iterative reconstruction

FBP ASIR StatisticalSeconds A bit longer Much longer

CT-based AC in PET-CT: sources of artefactsCT breathing protocols Metal artifacts

Intravenous contrast Oral contrast

Bolus of iv contrast may cause artefacts in PET image. Can be identified on CT and uncorrected PET image. Use saline flush to reduce effect

Oral contrast CT Corrected Uncorrected

Sources of artefacts in PET-CT: contrast agents

CORRECTEDNOT CORRECTEDOriginal CT Segmented CT

Bone

Contrast

medium

Ahmadian et al. (2008) Eur J Nucl Med Mol Imaging 35: 1812-1823

Transverse Coronal Transverse Coronal

Abdoli et al Med Phys (2010)

Uncorrected Sinogram Corrected Sinogram

Un

co

rre

cte

d

ima

ge

sC

orr

ec

ted

ima

ge

s

Abdoli et al Eur J Nucl Med Mol Imaging (2011)

Sources of artefacts in PET-CT: metallic objects

Metal artefact reduction in diagnostic quality CT

Mehranian et al IEEE Trans Med Imaging (2013)

Spatial Resolution Ingenuity TF PET-MR Gemini TF PET-CT (Surti et al. 2007)

FWHM (mm) FWTM (mm) FWHM (mm) FWTM (mm)

Transverse, 1 cm 4.7 ± 0.1 9.4 ± 0.2 4.8 9.7

Axial, 1 cm 4.6 ± 0.1 9.5 ± 0.1 4.8 9.6

Radial, 10 cm 5.0 ± 0.1 9.9 ± 0.1 5.2 10.3

Axial, 10 cm 5.0 ± 0.1 9.7 ± 0.1 4.8 9.6

Tangential, 10 cm 5.3 ± 0.1 10.5 ± 0.1 5.2 10.2

Performance evaluation of PET/MRI

PET-guided radiation therapy treatment planning

Therapy ConnectivityPET and CT DICOM

Established connectivity with most consoles

CT planning

PET/CT planning

Images of a patient with non-small cell lung cancer of the right upper lobe. PET/CT

allowed excluding associated atelectasis that was impossible using the CT alone

PET/CT improves RX treatment planningZaidi et al (2009) Acad Radiol

PET/CT

5.36 cm

CT

How to delineate the GTV?

5.48 cm

PET

3.47 cm

PET

100%

0

50%

0

100%

0

Zaidi & El Naqa (2010) EJNMMI

3D rendered image of the structures can be visualized

Allows filtering undesired structures such as brain, heart, and small

artifacts

Reports all lesion statistics in a

Microsoft Excel file

Automated lesion quantification

Volume Rendered “Very Hot” Tissues

Phantom simulation studies

Abdoli et al Med Phys (2013)

Segmentation method Mean volume (cc) SOI RE (%) CE (%)

Nestle 35.51 0.80 19.11 24.63

FCM 23.45 0.76 -21.33 23.70

FCM-SW 27.29 0.83 -8.44 16.99

Active contour 29.94 0.85 0.44 16.18

True volume 29.81 - - -

SOI= Spatial Overlap Index RE= Relative Error CE= Classification Error

XCAT model

Automated lesion quantification

Automated lesion quantification

-100.00

-50.00

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250.00

Nestle FCM FCM-SW Active Contour

Me

an

Re

lativ

e E

rro

r(%

)

-9.58

0.29

FCM-SW Active Contour

Abdoli et al Med Phys (2013)

Clinical studies

0.00

50.00

100.00

150.00

200.00

250.00

300.00

Nestle FCM FCM-SW Active Contour

Me

an

Cla

ssif

icatio

n

Erro

r (

%) 39.24 40.16

FCM-SW Active Contour

0.47 0.50

0.66 0.67

0.00

0.10

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Nestle FCM FCM-SW Active

ContourS

OI

Summary

The medical physics expert # a super technologist (Technicien de luxe)

The role of the medical physics expert should not be limited to doing QA/QC

The medical physics expert need to be actually doing medical physics, not

spending too much time on administration, business, grant writing, scientific

politics and unnecessary committee and professional society work … “He

should at the very least, stay active part-time research worker and/or clinical service scientist”

The medical physics expert should be talented and have plenty of additional

skills to be able to handle complex issues efficiently. He should also be

clever, diplomatic and excellent communicators to convince administrators

(usually inexperts in applications of science in medicine) about the importance of their work and its implications on healthcare delivery.