Session II.3.10 Part II Quantities and Measurements Module 3 Principles of Radiation Detection and Measurement Session 10 Imaging Detectors Now let’s discuss various kinds of radiation imaging detectors, their principles of operation, and their applications. IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources

Introduction Radiation imaging detectors and their principles of operation will be discussed Students will learn about film radiographic imaging, rectilinear scanners, total performance phantoms, gamma cameras, cardiothoracic imaging, bone scans, computerized tomography, SPECT nuclear imaging, ECG-gated tomography, QA/QC issues, and positron emission tomography (PET)

Content Film radiographic imaging Rectilinear scanners Total performance phantoms Gamma cameras Cardiothoracic imaging Bone scans Computerized tomography SPECT nuclear imaging ECG-gated tomography QA/QC issues Positron emission tomography (PET)

Overview Principles of nuclear imaging will be described Examples of radiation imaging detectors and their applications will be discussed

Film Radiographic Imaging X-ray imaging is a method of illuminating the body with a penetrating high energy ionizing radiation. The differential absorption of this radiation by the various tissues of the body creates on film an inverse shadow of the body. Less dense, lower atomic weight structures, such as the lung, allow transmission of more radiation flux producing greater fluorescence on an absorbing screen which exposes an adjacent film more densely, making those areas black. Higher atomic weight structures (bone) absorb and block the radiation, thus do not result in the exposure of the silver halide grains in the film emulsion, and so bony structures such as the ribs appear white (transparent).

Nuclear Medicine Imaging Detectors Nuclear Medicine is a method of obtaining diagnostic images by giving the patient a small dose of radioactive isotope Pictures are then taken with a special camera which is able to detect the location of the radio-pharmaceutical in the body and create images which the physician can evaluate

Nuclear Medicine Imaging Detectors The radioisotope dose is given either by an IV injection in the arm, breathing an aerosol, or swallowing a capsule The radioactive isotope is combined with a "tag“ substance which will make it collect in the organ or system the doctor wants to evaluate

Nuclear Medicine Imaging Detectors How the dose is given is determined by the area of the body that is being studied The radiation dose to the body is comparable to an x-ray exam and there are no side effects with the materials used

Nuclear Medicine Imaging Detectors A camera will be used to take pictures The camera may be installed in the hospital or physician's clinic, or it may also be housed in a mobile imaging vehicle In both instances, the camera works the same way and gives the same results

Nuclear Medicine Imaging Detectors Some exams require a delay after the dose is given and before the pictures are started. This delay is required to give the dose time to collect in the organ being studied Bone scans, heart scans, and thyroid scans often have delays. Other exams, such as renal scans, start immediately after the dose is administered

Nuclear Medicine Imaging Detectors The patient may be asked to lie down or sit in front of the camera. The technologist will position the camera close to the area of the body that is to be imaged Scans range in time from a few minutes to several hours depending on the type of exam being done

Nuclear Medicine Imaging Detectors The camera does not have any effect on the body and the technologist makes the patient as comfortable as possible before starting the exam

Scanner drive mechanism Rectilinear Scanner Scaler Ampl. PHA Display processor Rate- meter Gain Base Window HV Voltage Display device Scanner drive mechanism

Used to measure the spatial distribution of a radiopharmaceutical Rectilinear Scanner Used to measure the spatial distribution of a radiopharmaceutical Rollo 1977

Collimator NaI (Tl) crystal Collimator crystal side Lead septa patient side Focal distance Focal plane Focal point

Collimator This image shows the point source sensitivity of a focussed collimator at different distances.

Scanner Images

Scanner Operational considerations: Scanning speed (optimum count density) Collimator Collimator mounting Tapper function Window setting Background

Scanner Quality Control Acceptance Daily Weekly Yearly Energy window P T T P Energy resolution P P Sensitivity P T P Counting precision P P Linearity of energy response P P Test of integral background P T P Test of preset analyzer facilities P P System linearity P T P Background subtraction P P Contrast enhancement P P Scanner drive P P Total performance P T P P = physicist T = technician

Total Performance Phantom

Gamma Camera Used to measure the spatial and temporal Siemens Nuclear medicine imaging is used when patients need functional or physiological evaluation. A small amount of a radio-pharmaceutical or "tracer" is injected into a patient's vein to evaluate how certain parts of the body are functioning. Used to measure the spatial and temporal distribution of a radiopharmaceutical

Gamma Camera The nuclear medicine gamma camera picks up the signals from the "tracer" and a computer translates these signals into images. The radiologist will study these images and send a report to the patient's doctor.

Gamma Camera Nuclear medicine images arise from injected radioactive tracers which subsequently emit radiation from within body organs. The radioactive compounds tend to be designed to accumulate selectively in specific tissues. For example, lung scans used in the diagnosis of pulmonary embolus arise from technetium-labeled macroaggregated albumin, which when injected into a vein, spreads and is deposited relatively evenly throughout normally perfused lung micro-vasculature. This creates an image solely of the lungs.

Gamma Camera (principle of operation) PM-tubes Detector Collimator Position X Position Y Energy Z

PM-tubes

Gamma Camera Collimators

Gamma Camera Data Acquisition Static Dynamic ECG-gated Wholebody scanning Tomography ECG-gated tomography Wholebody tomography

Dynamic Acquisition This is an example of a dynamic acquisition. First pass study of the heart with a high time resolution. A ROI is defined for the left ventricle and the corresponding time activity curve is displayed.

Cardiothoracic Imaging Coronary angiography requires multiple separate views to completely examine coronary anatomy and resolve potential vessel overlap. Several separate sequential injections of left (LCA) and right coronary arteries (RCA) are shown. Here, "postero -anterior" (PA), "left anterior oblique“ (LAO), and "right anterior oblique“ (RAO) views of a normal coronary tree are provided. The "Left Ventriculogram“ is an RAO view with direct contrast injection into the cavity to examine myocardial function.

Left Ventricle Time-Activity Curve

Bone Scans Bone scans can demonstrate the functioning of bone tissue. They can be used to demonstrate fractures, degenerative conditions or aid in the diagnosis of metastases. The triple phase bone scans are excellent in demonstrating stress or occult fractures as well as osteomyelitis. Prosthetic implants such as an artificial hip prosthesis can also be evaluated.

Whole Body Scanning Either the camera or the examination table moves

Tomographic Imaging Tomography is a "slicing" of the body into various sections and in various view planes. The tomographic sections when viewed in sequence or integrated by a computer allow the display and understanding of 3-dimensional anatomy. Medical images can be understood to belong to one of two main groups: tomographic or projection techniques. Projection techniques, such as x-ray films are "shadowgram-like“ transilluminations of the body. Because of the nature of trans-illumination, various tissues are imaged as overlapping each other and often need multiple views (thus the PA and Lateral) for visual understanding.

Computed Tomography Computed tomography is a digitally based x-ray technique. Like x-ray, the resulting images arise from differential x-ray absorption of tissue, a feature that rests primarily on atomic weight (and thus the electron density) of the various tissues. The technique uses a narrowly collimated x-ray beam to irradiate a slice of the body. The amount of radiation transmitted along each projection line is collected by photo-multiplier tubes and counted digitally. By rapidly acquiring views from numerous different projections, achieved by quickly rotating the tube and detectors around the body, the transmissivity of the body from different angles can be established externally. Once these transmission values are collected, they can be digitally filtered and back-projected mathematically (by a technique known as Fourier transformation) onto a matrix which represents fine differentiation of tissue densities. Mapping this density onto what is called the Hounsfield scale where bone is +1000 and air is -1000, resolves as subtle as 1/2 a percent electron density within half millimeter volumes of tissue. This distinction is enough to discriminate most of the soft tissue organs of the brain and abdomen, not to mention the lungs and mediastinum. Since the image is digital and represents a slice, multiple slices can be obtained and a volume estimated and displayed as a three-dimensional structure on a video display tube or film. Computed tomography has the advantage of rapid acquisition of images, but employs ionizing x-ray radiation which must be used conservatively to avoid harmful cumulative biologic effect.

CT Scanner The picture on top on this slide shows the Phillips 6000 Computerized Tomography (CT) imaging camera. Conventional CT can be used to scan a complete anatomical volume by making successive, stepwise scans of one slice after another. However, scanning a complete volume with this technique requires a delay between each scan, so that the table can be moved into position for the following scan. New technology avoids these delays by using Volumetric CT which combines continuous rotation and continuous radiation data collection with continuous patient table transportation. The data obtained can be submitted directly to the image reconstruction process resulting in 3D images of the anatomical site. Individual anatomical scans can be used to prescribe the radiation dose to the tumor site with minimal exposure to critical surrounding normal tissues. The figure on the bottom of this slide shows typical successive scans of the upper chest. The slice thickness is 5 mm. Dark areas are lung tissue and light areas image the heart.

SPECT Nuclear Imaging The Single Photon Emission Computed Tomography (SPECT) camera is a large scintillation crystal connected to multiple photo-multiplier tubes which detect radiation emanating from the body. The technology of single photon emission tomography arises from positioning the camera head at multiple angles around the body accumulating as many as 180° of views at specific angular intervals. A certain number of counts are obtained from each view. In some cases multi-headed cameras are used to increase the speed of acquisition. Software then allows integration of all individual projection views into a composite data set which can be re-displayed as tomographic slices. Obviously, patient or organ motion, as well as variations in attenuation from different viewpoints can have a profound effect on the quality of the tomographic view.

Cardiac Anatomy As Seen In SPECT Nuclear Imaging This slide shows an example of SPECT perfusion imaging. Nuclear myocardial perfusion tomograms using the radioactive compound technetium-99m sestamibi are shown compared to illustrations of the heart from similar views. Note that most of the myocardial wall activity arises from the left ventricular myocardium since it is considerably thicker (11 mm) than the right ventricular free wall (3 mm). The short axis tomogram shows the left ventricular myocardium as a donut shape while the vertical long axis and horizontal long axis tomograms display the myocardial wall as U-shaped structures.

Tomographic Acquisition

Tomographic Reconstruction This image should be used to explain the principle of filtered back projection. Note that the image contains an animation.

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

Myocardial Scintigrafi 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.

ECG-Gated Acquisition R Interval n Image n The ECG gated acquisition is a type of dynamic acquisition. The RR-interval is divided into a certain number of frames (16 to 32) where each frame then represents a certain phase (t) of the heart cycle. Each time the R-peak in the ECG is detected the collection of data starts in frame 1 during time t, then in frame 2 during time t and so on. The total acquisition time is generally about 10 min so the whole study represents several hundred heart cycles.

ECG-Gated Bloodpool Scintigraphy Example of 16 frames of an ECG gated acquisition in LAO projection. The first image (upper left) is the end diastolic image and the sixth image (2nd row) is the end systolic image.

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

Distribution of Radiopharmaceutical There are methods to change the radionuclide distribution. In this case (examination of the myocardium using Tc-99m sestamibi) the uptake in the liver and emptying of the gallbladder can be stimulated by giving the patient a fatty meal.

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

Resolution - Distance High sensitivity High resolution FWHM 30 25 20 FWHM (mm) 15 10 High resolution 5 2 4 6 8 10 12 14 16 Distance (cm)

Spatial Resolution - Distance Optimal Large distance

Uniformity & Linearity

Non Uniformity

Non Uniformity Cracked Crystal

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 Difference The lower image is the absolute difference between the upper two images. It clearly shows the ring artifacts.

Non-Uniformity Defect Collimator The images in the lower row are acquired using a collimator with 50% lower sensitivity in an 1 cm3 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

Count Rate Performance (IAEA QC Atlas)

Spatial Positioning at Different Energies Intrinsic spatial resolution with Ga-67 point source (count rate < 20k cps); quadrant bar pattern; 3M counts; preset energy window widths; summed image from energy windows set over the 93 keV, 183 keV and 296 keV photopeaks. (IAEA QC Atlas)

Spatial Positioning at Different Energies This image tries to illustrate the problem that could come up if the positioning of an absorption event is dependent on the energy of the photon. If the examination requires a subtraction of two images the result will depend on the positioning rather than the patient. The images are from a parathyroid scan. The left images show the result of subtraction of the upper two images and how the result will be affected by the offset in positioning. The image to the right shows the ”truth”.

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

The Amount Of Scattered Photons Registered Patient size Energy resolution of the gamma camera 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 ratio of 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 Tc-99m Full energy peak Scattered photons FWHM Overlapping area 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

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

Scatter Correction This is an illustration of the triple energy window scatter correction. Two narrow windows are used, one on each side of the full energy peak. This information is used to determine the amount of scatter in the full energy window, simply by interpolation. The left image is a planar thallium scan and the middle image is the calculated scatter image which is subtracted from the left image. The result is shown in the right image.

Attenuation I = I0 e(-µx) Register 1000 counts Origin of counts This figure explains the origin of the detected photons. It is purely theoretical. Assume an object 20 x 20 x 20 cm3 filled with Tc-99m. The diagram shows that 12% of the registered photons come from the first cm of the object. Only 4% of the registered photons comes from 10 cm and 1% from 20 cm. I = I0 e(-µx)

Attenuation Contrast (2 cm object) 23% 7% 2% 23% 7% 2% This is again the same theoretical phantom and the expected contrast in an image of a 2 cm thick object containing no activity.

Attenuation Correction

Attenuation Correction Transmission measurements Sealed source CT

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

QC Gamma Camera IAEA-TECDOC-602 Quality control of Nuclear medicine instruments 1991 INTERNATIONAL ATOMIC ENERGY AGENCY IAEA May 1991

QC Gamma Camera

Energy Resolution

Linearity Flood source or point source (Tc-99m) Bar phantom or orthogonal-hole phantom Subjective evaluation of the image Calculate absolute (AL) and differential (DL) linearity AL: Maximum displacement from ideal grid (mm) DL: Standard deviation of displacements (mm)

Uniformity Flood source (Tc-99m, Co-57) Point source (Tc-99m) Intrinsic uniformity: Point source at a large distance from the detector Acquire an image of 10,000,000 counts With collimator: Flood source on the collimator

Uniformity Subjective evaluation of the image Calculate Integral uniformity (IU) Differential uniformity (DU) Max-Min Max+Min IU = x 100 where Max is the maximum and Min is the minimum counts in a pixel DU = x 100 where Hi is the highest and Low is the lowest pixel value in a row of 5 pixels moving over the field of view. Matrix size 64x64 or 128x128 Hi-Low Hi+Low

Uniformity Different Radionuclides D BOULFELFEL Dubai Hospital

Linearity and Uniformity Corrections Dogan Bor, Ankara

Off Peak Measurements Dogan Bor, Ankara

Tomographic Uniformity Tomographic uniformity is the uniformity of the reconstruction of a slice through a uniform distribution of activity. SPECT phantom with 200-400 MBq Tc-99m aligned with the axis of rotation. Acquire 250k counts per angle. Reconstruct the data with a ramp filter.

Incorrect Measurement Two images of a flood source filled with a solution of Tc-99m, which had not been mixed properly

Flood source or point source. Spatial Resolution Flood source or point source. Bar phantom Subjective evaluation of the image

Spatial Resolution Intrinsic resolution System resolution Screw clip Polyethylene tubing about 0.5 mm in Internal diameter Rigid plastic 30 mm 50 mm 500 mm 60 mm 200 mm 5 mm Lead Plastic shims IAEA TECDOC 602

Spatial Resolution Tc-99m or other radionuclide in use Intrinsic: Collimated line source on the detector System: Line source at a certain distance Calculate FWHM of the line spread function FWHM: 7.9 mm This is an example of how to measure the spatial resolution from the line spread function. It also gives an example of the MTF.

Tomographic Resolution Measurements should be made with and without scatter Point or line source free in air Point or line source in a SPECT phantom

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%

Sensitivity

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

Multiple Window Spatial Registration Collimated Ga-67 sources are used at central point, four points on the X-axis and four points on the Y axis Perform acquisitions for the 93, 184 and 300 keV energy windows Displacement of count centroids from each peak is computed and maximum is retained as MWSR in mm

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

Count Rate Performance Use of decaying source or calibrated copper sheets to compute the observed count rate for a 20% count loss and the maximum count rate without scatter

Pixel Size The pixel size is used in several application programs for calculation of distance, surface and volume.

Center Of Rotation Point source of Tc-99m or Co-57 Make a tomographic acquisition In x-direction the position will describe a sine-function. In y-direction a straight line. Calculate the offset from a fitted cosine and linear function at each angle. Cosine function Linear function

Center Of Rotation These are transversal slices of a myocardial tomography. They show the possible effects of an offset in center of rotation. The matrix size is 64 x 64 and the pixel size is 5 mm. Equivalent to an offset in center of rotation is patient movement during acquisition.

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

Sources For QC of Gamma Cameras Point source Collimated line source Line source Flood source <1 mm Tc-99m, Co-57, Ga-67

Phantoms For QC of Gamma Cameras Bar phantom Slit phantom Orthogonal hole phantom Total performance phantom

Phantoms For QC Of Gamma Cameras

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

PET Positron Emission Tomography What is a PET scan? A Positron Emission Tomography (PET) scan is a procedure used to observe the brain, the heart, and tumors/cancers. For much of the past 20 years, PET scans have been a superb research tool for probing brain function and cardiac metabolism/blood flow. However, in the past five years, the clinical use of PET imaging has become apparent, especially in cancer imaging. The major reason PET scanning is assuming increased importance is because it can trace metabolic changes present in cancer cells which are different from normal tissues. In brief, cancers often have increased rates of blood flow, amino acid transport, protein synthesis, DNA synthesis, and glucose transport and use as compared with normal tissues. These qualitative metabolic changes can be detected by PET scanning with considerable efficiency. Therefore, the PET scan imaging method is assuming a growing role in the clinical practice of cancer imaging.

PET When is a PET scan used? Presently, doctors have been ordering PET scans in a growing number of clinical cases in oncology, cardiology, and neurology. A cancer doctor (oncologist) may order a PET scan to find: 1) abnormal tissue or tumors, 2) to determine appropriate treatment for a tumor, 3) to monitor response of cancers to therapy – is the cancer still alive or dead, and 4) to detect if a cancer has returned. Otherwise, a doctor may order this procedure to find: Early coronary artery disease, damaged or dead heart muscle, the effects of drugs on the heart and brain, early brain changes and diseases, and to look for areas affected by a stroke or blood clot. The numbers of uses of this powerful imaging tool seem to be increasing every day.

(511 keV) (511 keV) + + e- Annihilation Radionuclide Positron emitters always produce annihilation photons, each of energy 0.511 MeV. Since these two photons are emitted simultaneously and in opposite directions, they can be detected using coincidence counting, for example. Radionuclide

PET Scanner Principle Detector Detector

Principle Of Operation yes! Coincidence? Register event positions from both detectors. Reconstruct (Gerd Muehllehner et al 1994)

Flood response for a block detector PET Detectors A large number of scintillation crystals are coupled to a smaller number of PM-tubes. In the block detector, a matrix of cuts are made to define the detector elements. The light produced in each crystal will produce a unique combination of signals, which will allow the detector to be identified. M Dahlbom, UCLA Flood response for a block detector

Types of Coincidence Events “True” events result from coincidence between 2 photons from the same annihilation. Such events provide valid data. “Random” and “Scatter” events represent invalid data. These events are recorded by the system as misplaced “trues”, resulting in background noise that reduces image contrast and resolution. Line of “true” response Detected Line of “scatter” response Detected Undetected “random” response Metabolic Image Information Background Noise Siemens 42 6

PET Scanner M Dahlbom, UCLA

Radionuclides Radionuclide Halftime Particle energy (min) (mean) (MeV) Cu-62 9.2 1.3 Ga-68 68.3 0.83 Rb-82 1.25 1.5

TUMOUR STAGING WITH PET (F18-FDG) Clinical Use TUMOUR STAGING WITH PET (F18-FDG)

Factors Affecting Image Formation Detector efficiency (the probability that the detector registers an event when a gamma ray path intersects the detector. Depends on detector size and material) System sensitivity (the number of events registered by the scanner per unit activity. Depends on detector efficiency and system geometry)

Factors Affecting Image Formation Time resolution (the ability to accurately determine coincidence events.) Count-rate capability (the ability of the scanner to record events at high count rates. Depends on detector material and the properties of the electronic components) Spatial resolution (the ability to separate closely spaced objects. Depends on detector size, physics of positron decay, system geometry and detector material)

Operational Considerations Calibration check Normalization Blank scan Scanner cross calibration

Quality Control Calibration check Uniformity Spatial Resolution Scatter fraction Sensitivity Count rate losses and randoms Scanner cross calibration Drifts in coincidence timing

Quality Control Drifts in energy thresholds Mechanical movement of detector rings Removable septa positioning Laser alignment Attenuation correction accuracy Dead time correction accuracy Scatter correction accuracy Random coincidence correction accuracy

Factors Affecting Image Formation Random/scatter events Crystal thickness Dead time losses (fast electronic)

Image Quality Effects of Randoms/Scatter trues randoms & scatter Same image with increased counts but no change in the ratio of trues to randoms & scatter trues randoms & scatter Same image with same number of counts but a positive change in the ratio of trues to randoms & scatter trues randoms & scatter Typical coincidence image* containing a high percentage of randoms and scatter Siemens Superior Image Quality is the result of superior Count Quality 42 7

Contrast Enhancing Axial Shields Randoms (rejected) Scatter (rejected) Top View of Axial Shield Trues (counted) Side View of Axial Shield Siemens Primary Objective: Design Concept: Clinical Benefit: Reduce randoms and scatter originating from high activity organs outside the scan FOV (e.g. brain, heart, bladder) Specially designed lead strips equally spaced perpendicular to the axis of rotation. Similar to PET septa, but optimized for NaI coincidence Higher image contrast for improved lesion detectability 42 10

Crystal Thickness The probability of photon interaction increases with the crystal thickness The spatial resolution decreases with the thickness of the crystal Can this be optimized?

Summary Radiation imaging detectors and their principles of operation were discussed Students learned about film radiographic imaging, rectilinear scanners, total performance phantoms, gamma cameras, cardiothoracic imaging, bone scans, computerized tomography, SPECT nuclear imaging, ECG-gated tomography, QA/QC issues, and positron emission tomography (PET)

Where to Get More Information Knoll, G.T., Radiation Detection and Measurement, 3rd Edition, Wiley, New York (2000) Attix, F.H., Introduction to Radiological Physics and Radiation Dosimetry, Wiley, New York (1986) International Atomic Energy Agency, Determination of Absorbed Dose in Photon and Electron Beams, 2nd Edition, Technical Reports Series No. 277, IAEA, Vienna (1997)

Where to Get More Information International Commission on Radiation Units and Measurements, Quantities and Units in Radiation Protection Dosimetry, Report No. 51, ICRU, Bethesda (1993) International Commission on Radiation Units and Measurements, Fundamental Quantities and Units for Ionizing Radiation, Report No. 60, ICRU, Bethesda (1998)

Where to Get More Information Hine, G. J. and Brownell, G. L., (Ed. ), Radiation Dosimetry, Academic Press (New York, 1956) Bevelacqua, Joseph J., Contemporary Health Physics, John Wiley & Sons, Inc. (New York, 1995) International Commission on Radiological Protection, Data for Protection Against Ionizing Radiation from External Sources: Supplement to ICRP Publication 15. A Report of ICRP Committee 3, ICRP Publication 21, Pergamon Press (Oxford, 1973)

Where to Get More Information Cember, H., Introduction to Health Physics, 3rd Edition, McGraw-Hill, New York (2000) Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8th Edition, 1999 update), Wiley, New York (1999) International Atomic Energy Agency, The Safe Use of Radiation Sources, Training Course Series No. 6, IAEA, Vienna (1995)