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Physics of Nuclear Medicine Spect And Pet PowerPoint Presentation

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Description : Check out this medical PowerPoint presentation titled "Physics of Nuclear Medicine, SPECT and PET” by Jerry Allison, PhD.

This medical PowerPoint presentation is about SPECT and PET.

Nuclear medicine is a branch of medical imaging that uses radioactive substances to diagnose and treat various diseases. Two common techniques used in nuclear medicine are single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Both SPECT and PET rely on the physics of nuclear decay to create images of the bodys internal structures and functions.

SPECT imaging involves injecting a radioactive substance, called a radiotracer, into the patients bloodstream. The radiotracer emits gamma rays, which can be detected by a gamma camera. The gamma camera rotates around the patient, detecting the gamma rays and creating images of the distribution of the radiotracer in the body. SPECT images provide information about blood flow, tissue perfusion, and the function of organs such as the heart, lungs, and brain.

PET imaging uses radiotracers that emit positrons, which are positively charged particles. When a positron encounters an electron in the body, the two particles annihilate each other and emit two gamma rays in opposite directions. These gamma rays can be detected by a ring of detectors around the patient, which creates a three-dimensional image of the distribution of the radiotracer in the body. PET images provide information about metabolic activity, blood flow, and the function of organs such as the brain, heart, and lungs.

Both SPECT and PET rely on the physics of nuclear decay to create images of the body. Radioactive isotopes used in nuclear medicine emit radiation as they decay, and the behavior of this radiation is governed by the laws of physics. Understanding the physics of nuclear decay is essential for designing radiotracers, interpreting nuclear medicine images, and ensuring the safety of patients and medical personnel.

Tags : SPECT, PET, medical imaging, single-photon emission computed tomography, positron emission tomography, Nuclear Medicine, Nuclear Medicine PowerPoint presentation

Published on : Jun 20, 2023 | Views : 2308 | Downloads : 0

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Slide 1-

Physics of Nuclear Medicine, SPECT and PET Jerry Allison, Ph.D. Department of Radiology Medical College of Georgia Augusta University
Slide 2-

Outline Radionuclides in Nuclear Medicine Radiation Dose Gamma Camera Basics SPECT (Single Photon Emission Computed Tomography) PET (Positron Emission Tomography
Slide 3-

3 Radionuclides used in nuclear medicine Less than 20 radionuclides but hundreds of labeled compounds © Physics in Nuclear Medicine: Cherry, Sorenson and Phelps, 4th edition, 2012
Slide 4-

Effective dose of NM procedures 4
Slide 5-

5 Dose Definition Effective dose E (Sv): measure of absorbed dose to whole body, the product of equivalent dose and organ specific weighting factors Whole body dose equivalent to the nonuniform dose delivered
Slide 6-

How to obtain a NM image? Administer radiopharmaceutical (a radionuclide labeled to a pharmaceutical) The radiopharmaceutical concentrates in the desired locations Nucleus of the radionuclide decays to emit photons (g , x-ray) Detect the photons using a “gamma camera”
Slide 7-

Gamma Camera Basics
Slide 8-

Photomultiplier tube (PMT) 40 to 100 PM tubes (d = 5 cm) in a modern gamma camera photocathode directly coupled to detector or connected using plastic light guides ultrasensitive to magnetic fields
Slide 9-

Why collimator? – image formation Image of a point source is the whole detector. Image of a point source is a point. w/o collimator with collimator image collimator
Slide 10-

Why collimator? – image formation to establish geometric relationship between the source and image The collimator has a major affect on gamma camera sensitivity (count rate) and spatial resolution parallel-hole collimator
Slide 11-

Collimators 2015 Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR Most often used: parallel-hole collimator For thyroid and heart: pin-hole collimator For brain and heart: converging collimator
Slide 12-

Collimator Summary Collimator must be matched to energy of radionuclide Efficiency changes little with distance to source (patient) Resolution falls off quickly with distance to source (patient)
Slide 13-

Energy spectrum of detector energy window photopeak: all energy of g photons (E0) deposited in detector Septal penetration & scatter: energy deposited in detector is between 0 and E0.
Slide 14-

Photopeak All the energy of a g photon (E0) is deposited in the detector e.g. E0 = 140 keV for Tc-99m 14 or
Slide 15-

Septral penetration & scatter spectrum 15 Some of the energy of a g photon (E0) is deposited in the detector NOT USEFUL FOR IMAGING
Slide 16-

Modern Camera Design Most cameras use rectangular heads Most cameras are designed to do SPECT imaging The dual head is the most common design
Slide 17-

Tomographic imaging (SPECT) Tomographic images can be produced by acquiring conventional gamma camera projection data at several angles around the patient Similar to CT SPECT (Single Photon Emission Computed Tomography)
Slide 20-

Filtered Back Projection © Physics in Nuclear Medicine: Cherry, Sorenson and Phelps Attenuates streaks by filtering the projections
Slide 21-

Iterative Reconstruction Quantitatively more accurate Can model various corrections Collimator Scatter System geometry Detector resolution Slow Being used increasingly in SPECT
Slide 22-

Assume Some Image (I) Calculate Projections (P’) Calculation Includes Attenuation Scatter Blur with depth Compare to Measured Projection (P) Form New Image (I’) Use P’ & P to form corrections Is I-I’< * Done
Slide 23-

Data Collection Image matrix is collected 64 x 64 or 128 x 128 Each image row makes a slice Multiple slices can be added to reduce noise
Slide 24-

Attenuation correction:Chang Method Assume uniform attenuation m = linear attenuation coefficient of soft tissue (0.15 per cm for Tc-99m) X is tissue thickness along projection from emission data I(x) = I0e-mx
Slide 25-

Attenuation correction:Transmission measurements X-ray source (SPECT/CT) Non-diagnostic CT Diagnostic CT
Slide 26-

Positron decay characteristics Coincidence and angular correlation Time of flight PET detector/scanner design Data corrections PET (Positron Emission Tomography)
Slide 27-

Positron is an Anti-particle When a particle and and antiparticle interact they annihilate Both particles are destroyed Two photons(Gamma-rays) are created Two photons are emitted in ~opposite directions (± 0.25 degrees for F-18) + - Gamma 1 Gamma 2
Slide 28-

Where was the event? Coincidence ? PET Imaging Concepts
Slide 29-

Where was the event?
Slide 30-

Annihilation Detection Coincidence In coincidence counting an event is ONLY registered if a signal is received from two detectors within a narrow window of time. A few nanoseconds is usually used.
Slide 31-

Time-of-Flight PET Coincidence In “Time-of-Flight” pet, use of a very small time window (<100 picoseconds) can localize an annihilation event to within a few cm along the line of coincidence. Time-of-Flight PET can improve SNR.
Slide 32-

PET Scanner Ring (multiple rings) with lots of little detectors (up to 23,040) Rings have axial coverage of up to 26cm. Detectors must have good stopping power Detector must be fast for accurate coincidence measurements Lutecium silicate LSO (LYSO) is commonly used (&BGO)
Slide 33-

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Slide 34-

PET scanner PET scanners lack conventional collimation so they have a high geometric efficiency Some had septal rings to reduce cross talk from ring to ring When rings in 2D When rings out 3D Septa Septa
Slide 35-

Detector Needs High Stopping Power Much higher gamma ray energy (511 keV) Light Output Not as important because each gamma ray leaves a lot of energy in the crystal Short Decay Time Very important because of high count rate Limits activity given to patient
Slide 36-

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Slide 37-

Events in PET Scanners
Slide 38-

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Slide 39-

Trues
Slide 40-

Trues Rtrue = AO g2 gACDe-mT gACD~ h/2D for ring(s) Where Rtrue = true coincidence rate Ao = Administered activity g = intrinsic efficiency gACD = geometric efficiency e-mT = object attenuation h = detector thickness D = detector diameter
Slide 41-

Scatter
Slide 42-

Scatter-to-True Ratio .2 - .5 brain .4 -2 body Scatter (and Trues) are proportional to administered activity
Slide 43-

Random RRnd = CTW Rtrue Rtrue CTW = timing window
Slide 44-

Random-to-True Ratio .1 – 2 brain .1 -1 body Random-to-True Ratio high near high activity (Bladder)
Slide 45-

Corrections PET scanners use energy discrimination (pulse height analysis) system like the gamma camera to help eliminate scatter Randoms are corrected for by measuring coincidence rates with a delay of time between 511 keV photon arrivals (so there are no trues).
Slide 46-

Attenuation Correction Like all radionuclide imaging there is a problem due to attenuation. It is much less for PET than for Tc-99m imaging Correction is important for quantifying the metabolic activity of lesions (SUVs)
Slide 47-

Attenuation Correction CT data reconstructed to make a attenuation map of the body Attenuation map information is used in image reconstruction
Slide 48-

PET: CT Based Attenuation Correction © Nuclear medicine physics : a handbook for students and teachers, International Atomic Energy Agency, 2014
Slide 49-

SPECT vs PET SPECT PET (Step-and-shoot acquisition) (Simultaneous acquisition) 2015 Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR
Slide 50-

SPECT & PET SPECT – 2 views from opposite sides Res. ~ collimator res., which degrades rapidly with increasing distance from collimator face PET – Simultaneous acquisition Res. ~ detector width; is max in center of ring SPECT sensitivity ~ 0.02% Huge losses due to absorptive collimators PET sensitivity- 2D ~ 0.2%; 3D ~ 2% or higher High sensitivity due to ACD (electronic collimation) Allows higher frequency filters / higher spatial resolution 2015 Nuclear Medicine Physics for Radiology Residents Sameer Tipnis, PhD, DABR
Slide 51-

51 October 7, 2015 -- Researchers at the University of California, Davis (UC Davis) have received a five-year, $15.5 million grant to develop what they are calling the world's first total-body PET scanner. National Cancer Institute and will fund the Explorer project, led by Simon Cherry, PhD, distinguished professor of biomedical engineering and Ramsey Badawi, PhD, a professor of radiology. The total-body PET scanner would image an entire body all at once, and it would acquire images much faster or at a much lower radiation dose by capturing almost all of the available signal from radiopharmaceuticals. … the design would line the entire inside of the PET camera bore with multiple rings of PET detectors. … such a total-body PET design could reduce radiation dose by a factor of 40 or decrease scanning time from 20 minutes to 30 seconds http://www.auntminnie.com/index.aspx?sec=sup&sub=mol&pag=dis&ItemID=112051
Slide 52-

References Physics in Nuclear Medicine: Simon Cherry, James Sorenson and Michael Phelps, 4th Edition, Elsevier, 2012 International Atomic Energy Agency, SPECT/CT TECHNOLOGY & FACILITY DESIGN, https://rpop.iaea.org/ SPECT Single Photon Emission Computed Tomography, David S. Graff PhD, http://www.slideshare.net/david.s.graff/spect-presentation Quantitative capabilities of four state-of-the-art SPECT-CT cameras; Alain Seret, Daniel Nguyen and Claire Bernard, EJNMMI Research 2012, 2:45 Characterization of the count rate performance of modern gamma cameras, M. Silosky, V. Johnson, C. Beasley, and S. Cheenu Kappadath, Medical Physics 40, 032502 (2013) Nuclear medicine physics : a handbook for students and teachers, International Atomic Energy Agency, 2014
Slide 53-

References Physics in Nuclear Medicine: Simon Cherry, James Sorenson and Michael Phelps, 4th Edition, Elsevier, 2012 Physics of PET-CT, David S. Graff PhD, http://www.slideshare.net/david.s.graff/pet-ct-presentation The Challenge of Detector Designs for PET, Thomas K. Lewellen, AJR:195, August 2010 Basics of PET Imaging; Physics, Chemistry, and Regulations, Gopal B. Saha, Springer, 2005