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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: [email protected]
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
0.00
50.00
100.00
150.00
200.00
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
0.20
0.30
0.40
0.50
0.60
0.70
0.80
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.
