Download Scintillation Cameras for single-photon imaging (Planar and SPECT)

Review of Last Week:
Counting Statistics & Error Propagation
This week :
•  Types of Error
–  systematic error; eg bias in experiment, error with fixed tendency, cannot be treated with
statistics, can be corrected for if known (calibration) -- effects accuracy –  random error; inherent to instruments and/or nature of measurement (eg biological
variability), cannot be ‘corrected’ but can be minimized with large samples/trials, treated
with statistical approaches -- effects precision
Scintillation Cameras
for single-photon imaging
(Planar and SPECT)
•  Statistical Descriptions of Random Error
–  probability distribution functions
•  Binomial; probability of observing certain outcome in N attempts when probability
of single outcome is p.
•  Poisson (limiting case of binomial: p small, N large); mean = variance = (standard
deviation)2, asymmetric, positive means only
•  Gaussian (Normal); widely used, symmetric, approximates Poisson for large means,
mean and SD can be independent
William Hunter, PhD#
University of Washington#
Department of Radiology#
•  Reporting Statistics/Error - consistency in significant figures
Suggested reading: Chapters 13&14.Physics in Nuclear Medicine by Cherry et al.
•  Propagation of Error - errors from independent sources add in ‘quadrature’;
error in f(x, y) due to errors in x (x) and y (y) is f2 = |∂f/∂x|2x2 + |∂f/∂y|2y2
simplest case: f = ax ± by, then error in f: f2 = (ax)2 + (by)2
(a, b = const.)
The Planar Gamma Camera
Planar and SPECT Cameras - Summary
•  System components:
–  CollimatorDetectorElectronics
•  Collimator
–  Types: Parallel, Converging, Diverging, Pinhole, Multi-pinhole
–  Performance: Penetration, Resolution, Efficiency
•  Detector:
–  Components: Scintillator crystal, Optical spacer, PMTs
–  Performance: Efficiency, Intrinsic (spatial) resolution, Energy resolution
•  Acquisition modes:
–  Frame vs List mode
–  Static (single), Dynamic (TAC), Gated (cardiac / respiration)
•  Camera QA corrections:
–  Uniformity, Linearity, Photo-peak window, Multi-energy registration
•  SPECT QA/QC:
–  Center-of-rotation, Head tilt, uniformity
Siemens e.cam
1
Gamma Camera Instrumentation#
Signal#
The Scintillation Camera:
Detector System#
acquisition &#
processing#
computer#
processing#
electronics#
PMT#
Lightguide#
Scintillator#
Collimator#
Detection Efficiency#
Light response function versus position#
(spatial resolution)#
E
Intrinsic spatial
Resolution:
<4 mm FWHM
x1
x2
x3
x4
x5
x6
x7
x
0.64
PMT#
LG#
Crystal#
2
Gamma Camera Energy Spectra#
Scatter#
PMTs
detector - NaI(Tl)
Gamma Camera Energy Spectra#
Nai(Tl) Energy Spectra (140 keV)
6 104
•  Tc99m #
#140.5 keV #
# 6.03 hours#
4 104
•  I-131
#
#364, 637 keV
# 8.06 days#
3 104
•  I-123
#
#159 keV
#
# 13.0 hours#
•  I-125
#
#35 keV
#
# 60.2 days#
•  In-111
#
#172, 247 keV
# 2.81 days#
•  Th-201 #
#~70, 167 keV
# 3.044 days#
•  Ga-67
#93, 185, 300 keV# 3.25 days#
5 104
Counts
10% ER
20% ER
List of Nuclear Medicine
ʻSingle Photonʼ Radionuclides
2 104
1 104
0
0
50
100
150
energy (keV)
140 keV photons, 9.5 mm crystal#
200
#
From: Physics in Nuclear Medicine (Sorenson and Phelps)
3
Parallel Hole Collimator#
PMTs#
The Scintillation Camera:
Collimators#
Collimators - Septal Penetration#
Detector
Collimator
septa
l
d
t
detector - NaI(Tl)#
l e#
Collimator Efficiency#
Collimators typically absorb well
over 99.95% of all photons emitted
from the patient.
Trade-off between spatial resolution
and detection efficiency.#
Minimum septa thickness, t,
for <5% septal penetration:#
From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps)#
4
Collimator Resolution
Gamma Camera - spatial resolution
Rs =
(R
2
int
2
+ Rcol
)
From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps)
From: The Essential Physics of Medical Imaging (Bushberg, et al)#
Types of Collimators#
Collimator: Resolution and Sensitivity#
magnification
From: The Essential Physics of Medical Imaging (Bushberg, et al)#
From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps)
5
The Scintillation Camera:
Corrections and QA
Gamma Camera Processing Electronics
(energy correction)#
19
8
Energy channel vs. event location
9
6 104
5 104
17
7
6
2
1
10
3
4 104
11
Counts
18
3 104
2 104
1 104
16
5
4
10% ER (between)
10% ER (over)
12
0
0
50
100
150
200
energy (keV)
15
14
13
How was this image produced?
Gamma Camera Processing Electronics
(linearity correction)
Gamma Camera Processing Electronics
(linearity correction)
19
18
17
8
7
6
16
2
1
5
15
9
10
3
4
14
11
12
13
From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps)
6
Additional Gamma Camera Corrections
(sensitivity / uniformity)
Daily Gamma Camera QA Tests#
Acquired from long uniform flood after energy
and linearity corrections have been applied#
#
Multiplicative correction#
#
Adjusts for slight variation in the detection
efficiency of the crystal#
#
Compensates for small defects or damage to
the collimator#
Flood uniformity#
#
Should not be used to correct for large
irregularities#
Photopeak window#
From: The Essential Physics of Medical Imaging (Bushberg, et al)#
Multienergy spatial registration
(e.g., Ga-67 (93-, 185-, and 300 keV) gamma rays)#
properly adjusted#
Spatial Resolution Test#
improperly adjusted#
FWHM of LSF = 1.7 x (size of smallest bar resolved)#
From: The Essential Physics of Medical Imaging (Bushberg, et al)#
From: The Essential Physics of Medical Imaging (Bushberg, et al)#
7
Pulse Pile-up#
The Scintillation Camera:
Image Acquisition#
Pile-up in image
Energy spectra
From: Physics in Nuclear Medicine (Sorenson and Phelps) and (Cherry, Sorenson and Phelps)
Image Acquisition
Gated Acquisition
•  Frame mode (data stored as an image)#
-  static#
-  single image acquisition#
-  can have multiple energy windows#
-  dynamic#
-  series of images acquired sequentially#
-  gated#
-  repetitive, dynamic imaging#
-  used for cardiac imaging#
•  List-mode (data stored event by event)#
-  time stamps are included within data stream#
-  allows for flexible post-acquisition binning#
-  can result in very large data files#
From: The Essential Physics of Medical Imaging (Bushberg, et al)#
8
Region of Interest (ROI) and Time-Activity
Curves (TAC)
The Scintillation Camera:
SPECT Imaging
From: The Essential Physics of Medical Imaging (Bushberg, et al)
Gamma Camera Imaging
(SPECT)
Gamma Camera Imaging (SPECT)
Siemens e.cam (http://www.medical.siemens.com)
www.medical.philips.com
GE MG (http://www.gehealthcare.com)
www.medical.philips.com
9
Gamma Camera Imaging
(gated cardiac SPECT)
Additional QA/QC Tests for SPECT
Center-of-Rotation (COR) Alignment Artifact
Small COR misalignement will
blur image, while larger
misalignement will cause donut
shape artifacts.
•  Images obtained during
individual phases of cardiac
cycle
•  Gating based on EKG
•  8-16 frames per cycle
•  Allows assessment of global
and regional LV function
www.cardiology.utmb.edu/ slides/Gated%20Cardiac%20SPECT.htm
www.medical.siemens.com/siemens/en_INT/ gg_nm_FBAs/files/
brochures/Cardiology_Insert_4DMSPECT.pdf
Additional QA/QC Tests for SPECT
Camera Head Tilt
From: The Essential Physics of Medical Imaging (Bushberg, et al)
Additional QA/QC Tests for SPECT
Detector non-uniformity artifact
Rings around
center of rotation
(transverse view)
This artifact differs from a COR-misalignment
artifact in that it only appears around the AOR.
From: The Essential Physics of Medical Imaging (Bushberg, et al)
From: The Essential Physics of Medical Imaging (Bushberg, et al)
10
Planar and SPECT Cameras - Summary
•  System components:
–  CollimatorDetectorElectronics
•  Collimator
–  Types: Parallel, Converging, Diverging, Pinhole, Multi-pinhole
–  Performance: Penetration, Resolution, Efficiency
•  Detector:
–  Components: Scintillator crystal, Optical spacer, PMTs
–  Performance: Efficiency, Intrinsic (spatial) resolution, Energy resolution
•  Acquisition modes:
–  Frame vs List mode
–  Static (single), Dynamic (TAC), Gated (cardiac / respiration)
•  Camera QA corrections:
–  Uniformity, Linearity, Photo-peak window, Multi-energy registration
•  SPECT QA/QC:
–  Center-of-rotation, Head tilt, uniformity
11