Download SPECT/CT Imaging- Physics and g g y Instrumentation Issues

SPECT/CT Imagingg g Physics
y
and
Instrumentation Issues
Michael King, Ph.D.
Professor of Radiology
University of Massachusetts Medical School
Disclosure:
Di
l
D
Dr. Ki
King h
has research
h grants
t ffrom NIH
and Philips Medical Systems.
Slides not to be reproduced without permission of author
Outline 0f Talk
1. Introduction – Multi-Modality
y Imaging
g g
2. Components of SPECT/CT’s
3. Reasons for Combining a CT with a
y
SPECT System
4. Radiation Dose
5. References
Slides not to be reproduced without permission of author
Introduction – Multi-Modalityy Imaging
g g
• Multi-modality Imaging allows for the synthesis of
information (anatomy and function).
function)
y
is image
g registration
g
• Keyy to synthesis
• Tremendous amount of outstanding studies on
i
image
registration
i
i b
but:
- What if patient is on different table
table, positioned
differently, or can’t see fiducials?
- What if the other modality images do not exist?
Slides not to be reproduced without permission of author
Introduction – Multi-Modalityy Imaging
g g
• SPECT/CT – Bruce Hasegawa and team at UCSF Early
1990’s
A prototype CT/SPECT system was configured at the
UCSF Physics Research Laboratory within the
Department of Radiology. It combined a GE 600 XR/T
SPECT system with a GE 9800 Quick CT scanner for
correlated anatomical and functional imaging.
(http://www.radiology.ucsf.edu/physics/dualmodality)
• Why has combination of CT with SPECT not replaced
standalone SPECT system as PET/CT has for PET?
- SPECT systems cost less than state-of-art CT
- AC standard in PET and CT faster than radionuclide
transmission
- A lot of general nuclear medicine is performed with planar
as opposed to SPECT imaging
Components
p
of SPECT/CT- SPECT
• Radionuclide(s) which emits one or
more discrete energy photons.
• Collimators – match radionuclide –
need to be changed.
• Camera Heads – Keep close while
circling patient for best imaging.
• Variable angle bet
between
een camera
heads.
• Speed of rotation is limited for CT if
detector and tube are on same gantry
as camera heads.
Slides not to be reproduced without permission of author
Components
p
of SPECT/CT- CT
Bushberg,
B
hb
et.
t al.l The
Th E
Essential
ti l Ph
Physics
i off M
Medical
di l
Imaging, 2nd Edition, Lippincott Williams & Wilkins, 2002
•
•
•
•
Tube from Siemens CT
System
Electrons flow from cathode to anode
kV = max keV
kVp
k V
mA (mCoul/sec)
Time = sec
Slides not to be reproduced without permission of author
Components of SPECT/CT- CT
Bushberg, et. al.
The Essential
Physics of Medical
Imaging, 2nd
Edition, Lippincott
Williams & Wilkins,
2002
• X-ray tube emits polychromatic beam of
Bremsstrahlung x-rays, plus small number of
discrete characteristic x-rays
• Lower energy x-rays decreased by filtration
(inherent added
(inherent,
added, and patient)
Slides not to be reproduced without permission of author
Components of SPECT/CT- CT
Kalender WA,
Computed
Tomography,
Publicis MCD
Verlag,
Munich, 2000
• First
Fi t Generation
G
ti – translate
t
l t / rotate
t t
• I0 = intensity no patient present
• I = intensity with patient
Slides not to be reproduced without permission of author
Components of SPECT/CT- CT
Kalender WA, Computed Tomography, Publicis MCD Verlag, Munich, 2000
• Fan-beam with detector and tube rotating together.
• Spiral / Helical – Slip-Ring - axial interpolation
• Multi-Detector Array – Isotropic voxel size –>
R di ti D
Radiation
Dose
Slides not to be reproduced without permission of author
Components of SPECT/CT- Choices
• SPECT and
d CT on same or abutted
b tt d gantries?
ti ?
- Diagnostic quality – use of contrast
- Cardiac and / or general
- Respiratory or EKG gating
- Speed of acquisition (either is sequential)
- Room size, control room, shielding
- Cost
• Table – how supported so that can maintain registration
between SPECT and CT imaging with patient on table?
• Need both CT and Nuclear Technologist
Slides not to be reproduced without permission of author
Reasons for Combining – Attenuation
Map for AC
• Advantages Over Transmission Imaging
- Less Noise
- Better spatial resolution
- No cross-talk
- No radioactive source to replace
- Acquisition Time
• Concerns
- Sequential
O’Connor MK, et al.
9:361-376, 2002
- Polychromatic beam to discrete photon JNC
energies
- Contrast
- Respiratory and Body Motion
- Radiation dose
Slides not to be reproduced without permission of author
Reasons for Combining – Attenuation
Map for AC
Mismatch causes problem in the lateral
and anterior walls of cardiac studies.
They saw up to a 30% difference.
Le Meunier L, JNC 13: 821-830, 2006.
Slides not to be reproduced without permission of author
Reasons for Combining – Anatomy to
Correlate with Function
• Advantages
- Functional Images do not provide detailed anatomy
- Numerous articles point out advantages for using
combination in terms of diagnosis, staging, and followup of patients.
- See for example Oct 2006 and Jan 2007 issues of
Seminars in Nuclear
N clear Medicine dedicated to SPECT/CT
• Concerns
- Need for contrast?
- High radiation dose of extra diagnostic CT
g
low dose CT with existing
g diagnostic
g
CT
- Register
- Respiratory and body motion
Slides not to be reproduced without permission of author
Reasons for Combining – Anatomy to
C
Correlate
l t with
ith F
Function
ti
8 year old, pain left hip, MRI and x-ray no clear abnormality,
referred bone scan, AVN
Provided by Dr Stephen Scharf, Lenox Hill Hospital, NY
Slides not to be reproduced without permission of author
Reasons for Combining – Use Anatomy
to Define ROI’s and PVE Correction
• Advantages
- ROI used for quantification of activity
-
Absolute blood flow in heart (3-vessel disease, coronary artery
flow reserve capacity
capacity, and longitudinal studies)
-
Quantification of radiation dose for therapy
- Edges
g are many
y times easier to define in CT studies
- Template for correction of “partial volume effect”
• Concerns
- Need for contrast to define structure
- Anatomy / function mismatch
- Respiratory
R
i t
and
db
body
d motion
ti
Slides not to be reproduced without permission of author
Reasons for Combining – Use Anatomy to
Define ROI’s
ROI s and PVE Correction
Template
p
p
projection-reconstruction
j
method of UCSF applied
pp
to p
porcine model
Assign 1.0 to voxels in CT derived Template, project, and reconstruct
mimicking SPECT
Divide reconstructed template voxel by voxel into voxels in SPECT slices
within original template and sum – (within 10-15%).
Slides not to be reproduced without permission of author
Da Silva et al, J Nuc Med 42: 772-779, 2001
Radiation Dose – Cause for Concern
% of Total Collective Effective Dose US Population in 2006 From All
Sources
Radon and
Thoron (37%)
Computed
Tomography
(24%)
Nuclear
Medicine (12%)
Rest (27%)
Adapted From NCRP Report No 160 - 2009
Slides not to be reproduced without permission of author
Radiation Dose – Example
Effective Doses (mSv)
•
•
•
•
•
•
Diagnostic CT of abdomen
13.71
CT used for AC (Hawkeye)
0.72
Radionuclide transmission imaging
<0.023
Tc-99m MIBI Cardiac SPECT Study
6.41
Tl-201 Cardiac SPECT Study
10.01
Risk Cancer Death (LNT Model)
0.000054
1 M.
1.
M G.
G Stabin.
Stabin JNM 49:1555-1563
49:1555-1563, 2008
2. L. J. Sawyer, et al. Nuc Med Comm 29:144-9, 2008
3. K. Van Laere, et al. JNM 41:2051-2062, 2000
4. E. J. Hall + A. J. Giaccia Radiobiology for the Radiologist, 2006
Slides not to be reproduced without permission of author
Radiation Dose – Ways
y to
Reduse Dose
• Filter beam to “harden” it.
• Reduce mA when ever possible – automatic exposure
control
• Use low-dose CT with SPECT and register using this
CT to existing diagnostic CT when available
• Use iterative reconstruction to reduce noise in slices
Slides not to be reproduced without permission of author
References
• JT Bushberg, et al. The Essential Physics of Medical
Imaging Lippincott Williams & Williams2nd Ed
Imaging.
Ed, 2002
• WA Kalender. Computed Tomography. Wiley 2nd Ed, 2006
•HZ
Zaidi,
idi B H
Hasegawa. JNM 44
44:291-315,
291 315 2003
• MK O’Connor, BJ Kemp. Sem NM 36:258-266, 2006
• JA Patton, TG Turkington. JNMT 36:1-10, 2008
• AK Buck, et al. JNM 49:1305-1319, 2008.
• DJ Brenner, EJ Hall. NJM 357:2277-84, 2007
Slides not to be reproduced without permission of author