scintillation cameras for single-photon imaging (planar

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Review of Last Week:��Counting Statistics & Error Propagation

•  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

•  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

•  Reporting Statistics/Error - consistency in significant figures •  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|2x

2 + |∂f/∂y|2y2

simplest case: f = ax ± by, then error in f: f2 = (ax)2 + (by)2 (a, b = const.)

This week :��

Scintillation Camerasfor single-photon imaging

(Planar and SPECT) William Hunter, PhD#

University of Washington#Department of Radiology#

Suggested reading: Chapters 13&14.Physics in Nuclear Medicine by Cherry et al.

Planar and SPECT Cameras - Summary •  System components:

–  CollimatorDetectorElectronics

•  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

The Planar Gamma Camera

Siemens e.cam

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acquisition &#processing#computer#

Gamma Camera Instrumentation#

Signal#processing#electronics#

Scintillator#Lightguide#

PMT#

Collimator#

The Scintillation Camera: Detector System#

Detection Efficiency#

0.64

Light response function versus position#(spatial resolution)#

x

E

x7 x6 x5 x4 x3 x2 x1

Crystal#LG#

PMT#

Intrinsic spatial Resolution: <4 mm FWHM

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Scatter#

detector - NaI(Tl)

PMTs

Gamma Camera Energy Spectra#

0

1 104

2 104

3 104

4 104

5 104

6 104

0 50 100 150 200

Nai(Tl) Energy Spectra (140 keV)

10% ER20% ER

Count

s

energy (keV)

Gamma Camera Energy Spectra#

140 keV photons, 9.5 mm crystal#

List of Nuclear Medicine ʻSingle Photonʼ Radionuclides •  Tc99m # #140.5 keV # # 6.03 hours#•  I-131 # #364, 637 keV # 8.06 days#•  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#

From: Physics in Nuclear Medicine (Sorenson and Phelps)

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The Scintillation Camera: Collimators#

Parallel Hole Collimator#

detector - NaI(Tl)#

PMTs#

le#

Collimators - Septal Penetration#

Minimum septa thickness, t, for <5% septal penetration:#

From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps)#

Detector

l

d t

Collimator septa

Collimator Efficiency#

Collimators typically absorb well over 99.95% of all photons emitted from the patient. Trade-off between spatial resolution and detection efficiency.#

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From: The Essential Physics of Medical Imaging (Bushberg, et al)#

Collimator Resolution Gamma Camera - spatial resolution

Rs = Rint2 + Rcol

2( )

From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps)

Types of Collimators#


magnification


Collimator: Resolution and Sensitivity#

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The Scintillation Camera: Corrections and QA

How was this image produced?

Gamma Camera Processing Electronics(energy correction)#

2

3

45

6

7

8

10

11

12

131415

9

16

17

18

19

1

0

1 104

2 104

3 104

4 104

5 104

6 104

0 50 100 150 200

Energy channel vs. event location

10% ER (between)10% ER (over)

Cou

nts

energy (keV)

Gamma Camera Processing Electronics(linearity correction)

2

3

45

6

7

8

10

11

12

131415

9

16

17

18

19

1


Gamma Camera Processing Electronics(linearity correction)

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Additional Gamma Camera Corrections (sensitivity / uniformity)

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##Should not be used to correct for large irregularities#

Daily Gamma Camera QA Tests#

Photopeak window#

Flood uniformity#


Multienergy spatial registration (e.g., Ga-67 (93-, 185-, and 300 keV) gamma rays)#


properly adjusted# improperly adjusted#

Spatial Resolution Test#


FWHM of LSF = 1.7 x (size of smallest bar resolved) #

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Pulse Pile-up#

From: Physics in Nuclear Medicine (Sorenson and Phelps) and (Cherry, Sorenson and Phelps)

Energy spectra

Pile-up in image

The Scintillation Camera: Image Acquisition#

Image 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#

Gated Acquisition


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Region of Interest (ROI) and Time-Activity Curves (TAC)

From: The Essential Physics of Medical Imaging (Bushberg, et al)

The Scintillation Camera: SPECT Imaging

Gamma Camera Imaging (SPECT)

Siemens e.cam (http://www.medical.siemens.com)

GE MG (http://www.gehealthcare.com)

www.medical.philips.com

Gamma Camera Imaging (SPECT)

www.medical.philips.com

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Gamma Camera Imaging (gated cardiac SPECT)

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

•  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

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.

Additional QA/QC Tests for SPECT Camera Head Tilt


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.

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Planar and SPECT Cameras - Summary •  System components:

–  CollimatorDetectorElectronics

•  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

scintillation cameras for single-photon imaging (planar

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