RAD 466-L 8 by Dr. Halima Hawesa SPECT/CT TECHNOLOGY & FACILITY DESIGN RAD 466-L 8 by Dr. Halima Hawesa

Objective To become familiar with basic SPECT/CT technology, and review considerations in establishing a new SPECT/CT facility

Content SPECT cameras Image Quality & Camera QA SPECT/CT scanners Design of SPECT/CT facilities

What is SPECT Camera gamma cameras. The most widely used gamma cameras are the so-called Anger cameras, in which a series of phototubes detects the light emissions of a large single crystal, covering the field of view of the camera. SPECT imaging systems consist of single- or multiple-head gamma cameras which rotate around the patient, thereby acquiring the projections necessary for reconstruction of axial slices. SPECT stand for Single Positron Emitting Computing Tomography.

SPECT Camera Components Collimator NaI(Tl) crystal Light Guide (optical coupling) PM-Tube array Pre-amplifier Position logic circuits (differential & addition etc.) Amplifier (gain control etc) Pulse height analyser Display (Cathode Ray Tube etc).

Scintillators Density Z Decay Light Atten . (g/cc) time yield length (ns) (% NaI) (mm) Na(Tl) I 3.67 51 230 100 30 BGO 7.13 75 300 15 11 LSO 7.4 66 47 75 12 GSO 6.7 59 43 22 15 BGO - Bismuth Gremanate LSO - Lutetium Oxyorthosilicate GSO - Gadolinium Oxyorthosilicate Na(Tl) I works well at 140 keV, and is the most common scintillator used in SPECT cameras

Scintillation detector Amplifier PHA It is important to explain why there is a proportionality between the photon energy absorbed in the detector and the pulse height Scaler

Pulse height analyzer Pulse height (V) UL LL Time The pulse height analyzer allows only pulses of a certain height (energy) to be counted. counted not counted

Gamma camera Used to measure the spatial and temporal distribution of a radiopharmaceutical

GAMMA Camera

Gamma camera (principle of operation) Position X Position Y Energy Z PM-tubes Detector Collimator Types of collimator Pinhole Parallel hole Diverging Converging collimators.

GAMMA CAMERA Photons are selected by a collimator, hits the detector crystal, which produce light flashes that are detected and amplified by the photomultipliers, then send to digitizer, and then to computer processor for image reconstruction, then to display on monitor.

PM-tubes Detect and amplify the light flash produced by the scintillation crystal.

GAMMA-ray Scintillation Detector gamma-ray energy converted to light Light converted to electrical signal Photomultiplier Tube gamma-Rays Light Electrical Signal Scintillation Crystal

Photomultiplier Tubes Light incident on Photocathode of PM tube Photocathode releases electrons + - gamma-Rays Light Scintillation Crystal Photocathode PM Tube Dynodes

Photomultiplier Tubes Electrons attracted to series of dynodes each dynode slightly more positive than last one + + + - + + gamma-Rays Light Scintillation Crystal Photocathode PM Tube Dynodes

Gamma camera Data acquisition Static Dynamic ECG-gated Wholebody scanning Tomography ECG-gated tomography Wholebody tomography

Scintigraphy seeks to determine the distribution of a radiopharmaceutical There are methods to change the radionuclide distribution. In this case (examination of the myocaedium using Tc99 sestamibi) the uptake in the liver and emptying of the gallbladder can be stimulated by giving the patient a fatty meal.

SPECT cameras are used to determine the three-dimensional distribution of the radiotracer

Tomographic acquisition

Tomographic planes The image can be used to illustrate that gammacamera tomography is imaging of a volume where slices can be displayed in any plane.

Myocardial scintigraphy This is an example of a surface rendered image combined with the information in the coronal slices. The patient has an iscemic heart disease.

ECG GATED TOMOGRAPHY This is an animated image and shows the information in three tomographic planes as well as a surface rendered image to illustrate wall motion.

12.2 Image Quality & Camera QA

Factors affecting image formation Distribution of radiopharmaceutical Collimator selection and sensitivity Spatial resolution Energy resolution Uniformity Count rate performance Spatial positioning at different energies Center of rotation Scattered radiation Attenuation Noise

SPATIAL RESOLUTION Sum of intrinsic resolution and the collimator resolution Intrinsic resolution depends on the positioning of the scintillation events (detector thickness, number of PM-tubes, photon energy) Collimator resolution depends on the collimator geometry (size, shape and length of the holes)

SPATIAL RESOLUTION Object Image Intensity

NON-UNIFORMITY (Contamination of collimator) The image to the right is aquired after cleaning of the collimator (Contamination of collimator)

NON UNIFORMITY RING ARTIFACTS Good uniformity Bad uniformity The lower image is the absolute difference between the upper two images. It clearly shows the ring artifacts. Difference

NON-UNIFORMITY Defect collimator The images in the lower row are acquired using a collimator with 50% lower sensitivity in an 1cm3 area in the center of the field of view. The images in the upper row are from the same patient acquired with a good collimator. It is important to point out the risk of false positive results if the camera is not working perfectly, Defect collimator

Scattered radiation Scattered photon photon electron Remember that compton scattering is the dominating process in the attenuation of photons in soft tissue. photon electron

The amount of scattered photons registered Depends on 1- Patient size 2- Energy resolution of the gammacamera 3- Window setting

PATIENT SIZE In the case of a big patient some of the full energy photons that should have reached the gamma camera will be scattered in the patient. The relation scattered/full energy photons will increase with the volume of the patient.

Pulse height distribution Energy Counts 20 40 60 80 100 120 140 160 Tc99m Full energy peak Scattered photons The width of the full energy peak (FWHM) is determined by the energy resolution of the gamma camera. There will be an overlap between the scattered photon distribution and the full energy peak, meaning that some scattered photons will be registered. FWHM Overlapping area

Window width 20% 40% 10% The image can be used to discuss the optimum relation between sensitivity and image quality. Increased window width will result in an increased number of registered scattered photons and hence a decrease in contrast

ATTENUATION CORRECTION Transmission measurements Sealed source CT

ATTENUATION CORRECTION Ficaro et al Circulation 93:463-473, 1996

NOISE Count density

Gamma camera Operational considerations Collimator selection Collimator mounting Distance collimator-patient Uniformity Energy window setting Corrections (attenuation, scatter) Background Recording system Type of examination

QC GAMMA CAMERA Acceptance Daily Weekly Yearly Uniformity P T T P Uniformity, tomography P P Spectrum display P T T P Energy resolution P P Sensitivity P T P Pixel size P T P Center of rotation P T P Linearity P P Resolution P P Count losses P P Multiple window pos P P Total performance phantom P P P: physicist, T:technician

Sensitivity Expressed as counts/min/MBq and should be measured for each collimator Important to observe with multi-head systems that variations among heads do not exceed 3%

Multiple Window Spatial Registration Performed to verify that contrast is satisfactory for imaging radionuclides, which emit photons of more than one energy (e.g. Tl-201, Ga-67, In-111, etc.) as well as in dual radionuclides studies

Count Rate Performance Performed to ensure that the time to process an event is sufficient to maintain spatial resolution and uniformity in clinical images acquired at high-count rates

Total performance Total performance phantom. Emission or transmission. Compare result with reference image.

Phantoms for QC of gamma cameras Bar phantom Slit phantom Orthogonal hole phantom Total performance phantom

QUALITY CONTROL ANALOGUE IMAGES Quality control of film processing: base & fog, sensitivity, contrast

QUALITY ASSURANCE COMPUTER EVALUATION Efficient use of computers can increase the sensitivity and specificity of an examination. * software based on published and clinically tested methods * well documented algorithms * user manuals * training * software phantoms

SPECT/CT System

TYPICAL SPECT/CT CONFIGURATION The most prevalent form of SPECT/CT scanner involves a dual-detector SPECT camera with a 1-slice or 4-slice CT unit mounted to the rotating gantry; 64-slice CT for SPECT/CT also available

SPECT/CT Accurate registration CT data used for attenuation correction Localization of abnormalities Parathyroid lesions (especially for ectopic lesions) Bone vs soft tissue infections CTCA fused with myocardial perfusion for 64-slice CT scanners

The CT Scanner X ray tube X ray emission in all directions collimators

A look inside a rotate/rotate CT Detector Array and Collimator X Ray Tube

A Look Inside a Slip Ring CT Note: how most of the electronics is placed on the rotating gantry X Ray Tube Detector Array Slip Ring

What are we measuring in a CT scanner? We are measuring the average linear attenuation coefficient µ between tube and detectors The attenuation coefficient reflects how the x ray intensity is reduced by a material

Conversion of  to CT number Distribution of  values initially measured  values are scaled to that of water to give the CT number

Nuclear medicine application according to type of radionuclide Diagnostics Therapy Pure  emitter  () e.g. ; Tc99m, In111, Ga67, I123 Positron emitters (ß+)   e.g. : F-18 , ß- emitters   e.g. : I131, Sm153 Pure ß- emitters   e.g. : Sr89, Y90, Er169  emitters   e.g. : At211, Bi213

RADIOPHARMACEUTICALS Radiopharmaceuticals used in nuclear medicine can be classified as follows: ready-to-use radiopharmaceuticals e.g. 131I- MIBG, 131I-iodide, 201Tl-chloride, 111In- DTPA instant kits for preparation of products e.g. 99mTc-MDP, 99mTc-MAA, 99mTc-HIDA, 111In-Octreotide kits requiring heating e.g. 99mTc-MAG3, 99mTc-MIBI products requiring significant manipulation e.g. labelling of blood cells, synthesis and labelling of radiopharmaceuticals produced in house

Radionuclide used with SPECT 99mTc - Technetium

99Mo-99mTc GENERATOR 87.6% 99Mo 99mTc  140 keV T½ = 6.02 h 12.4% Technetium-99m is a metastable nuclear isomer of technetium-99, symbolized as 99mTc. The "m" indicates that this is a metastable nuclear isomer 87.6% 99Mo 99mTc Molybdenum 99  140 keV T½ = 6.02 h 12.4% ß- 442 keV  739 keV T½ = 2.75 d 99Tc ß- 292 keV T½ = 2*105 y 99Ru stable

Technetium generator Mo-99 Tc-99m Tc-99 NaCl AlO2 Mo-99 +Tc-99m Tc-99m 66 h 6h NaCl AlO2 Mo-99 +Tc-99m Tc-99m

Technetium generator Note that there different types of generators. This illustrates a dry type with a separate container of saline solution that is changed every time a new elution will be made. In the wet type of generator there is a built in container with enough volume of saline solution for all elutions

Technetium generator This is a closer look at the top of the generator with the needles where the elution vial and the saline solution vial are placed

Radiopharmaceuticals Radionuclide Pharmaceutical Organ Parameter + colloid Liver RES Tc-99m + MAA Lungs Regional perfusion + DTPA Kidneys Kidney function The image can be used for a short explanation of a radiopharmaceutical. The same radioactive substance can be used in labeling of different compunds resulting in radiopharmaceuticals with different properties

Laboratory work with radionuclides

Administration of radiopharmaceuticals

SUMMARY OF SPET/CT SPECT cameras are scintillation cameras, also called gamma cameras, which image one gamma ray at a time, with optimum detection at 140 KeV, ideal for gamma rays emitted by Tc-99m SPECT cameras rotate about the patient in order to determine the three-dimensional distribution of radiotracer in the patient SPECT/CT scanners have a CT scanner immediately adjacent to the SPECT camera, enabling accurate registration of the SPECT scan with the CT scan, enabling attenuation correction of the SPECT scan by the CT scan and anatomical localization of areas of unusually high activity revealed by the SPECT scan

SPECT/CT CLINICAL ALLPLICATIONS Refer to the pdf file included with this lecture (spect-appl-L8)