Spect

Seminar Report \u201903

SPECT

1. INTRODUCTION Emission Computed Tomography is a technique where by multi cross sectional images of tissue function can be produced , thus removing the effect of overlying and underlying activity. The technique of ECT is generally considered as two separate modalities. SINGLE PHOTON Emission Computed Tomography involves the use single gamma ray emitted per nuclear disintegration. Positron Emission Tomography makes use of radio isotopes such as gallium-68, when two gamma rays each of 511KeV, are emitted simultaneously where a positron from a nuclear disintegration annihilates in tissue. SPECT, the acronym of Single Photon Emission Computed Tomography

is

a

nuclear

medicine

technique

that

uses

radiopharmaceuticals, a rotating camera and a computer to produce images which allow us to visualize functional information about a patient\u2019s specific organ or body system. SPECT images are functional in nature rather than being purely anatomical such as ultrasound, CT and MRI. SPECT, like PET acquires information on the concentration of radio nuclides to the patient\u2019s body. SPECT dates from the early 1960 are when the idea of emission traverse section tomography was introduced by D.E.Kuhl and R.Q.Edwards prior to PET, X-ray, CT or MRI. THE first commercial Single Photon- ECT or SPECT imaging device was developed by Edward and Kuhl and they produce tomographic images from emission data in 1963. Many research systems which became clinical standards were also developed in 1980\u2019s.

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SPECT

2. Single photon emission computed tomography (SPECT) What is SPECT? SPECT is short for single photon emission computed tomography. As its name suggests (single photon emission) gamma rays are the sources of the information rather than X-ray emission in the conventional CT scan.

Why SPECT? Similar to X-ray, CT, MRI, etc SPECT allows us to visualize functional information about patient\u2019s specific organ or body system.

How does SPECT manage us to give functional information? Internal radiation is administrated by means of a pharmaceutical which is labeled with a radioactive isotope. This pharmaceutical isotope decays, resulting in the emission of gamma rays. These gamma rays give us a picture of what\u2019s happening inside the patient\u2019s body.

But how do these gamma rays allow us to see inside? By using the most essential tool in Nuclear Medicine-the Gamma Camera. The Gamma Camera can be used in planner imaging to acquire a 2-D image or in SPECT imaging to acquire a 3-D image.

How are these Gamma rays collected? The Gamma Camera collects the gamma rays emitted from the patient, enabling to reconstruct a picture of where the gamma rays originated. From this we can how a patient\u2019s organ or system is functioning.

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SPECT

3. THEORY AND INSTRMENTATION Single \u2013photon Emission Computed tomography or what the medical world refers to as SPECT is a technology used in nuclear medicine where the patient is injected with a radiopharmaceutical which will emit gamma rays. We seek the position and concentration of radionuclide distribution by the rotation of a photon detector array around the

body

which

acquires

data

from

multiple

angles.

The

radiopharmaceutical may be delivered by 1V catheter, inhaled aerosol etc. The radio activity is collected by an instrument called a gamma camera. Images are formed from the 3-D distribution of the radiopharmaceutical with in the body. Because the emission sources are inside the body cavity, this task is for more difficult than for X-ray, CT, where the source position and strength are known at all times. i.e. In X-ray, CT, the attenuation is measured not the transmission source. To compensate for the attenuation experienced by emission photons from injected tracers in the body, contemporary SPECT machines use mathematical reconstruction algorithms to increase resolution. The gamma camera is made up of two or three massive cameras opposite to each other which rotate around a centre axis, thus each camera moving 180 or 120 degrees respectively. Each camera is leadencased and weighs about 500 pounds .The camera has three basic layers \u2013the collimator (which only allows the gamma rays which are

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Seminar Report ’03

SPECT

perpendicular to the plane of the camera to enter), the crystal and the detectors. Because only a single photon is emitted from the radionuclide used for SPECT, a special lens known as a collimator is used to acquire the image from multiple views around the body .The collimation of the rays facilitates the reconstruction since we will be dealing with data that comes in only perpendicular .At each angle of projection, the data will be back projected only in one direction. When the gamma camera rotates around the supine body, it stops at interval angles to collect data. Since it has two or three heads, it needs to only to rotate 180 or 120 degrees to collect data around the entire body .The collected data is planar. Each of the cameras collects a matrix of values which correspond to the number of gamma counts detected in that direction at the one angle. Images can be reprojected into a three dimensional one that can be viewed in a dynamic rotating format on computer monitors, facilitating the demonstration of pertinent findings to the referring physicians.

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SPECT

4. THE GAMMA CAMERA

Once a radiopharmaceutical has been administered, it is necessary to detect the gamma ray emissions in order to attain the functional information. The instrument used in nuclear medicine for the detection of gamma rays is known as gamma camera(fig 4.1).

Fig. 4.1 Parts of Gamma Camera The components making up the gamma camera are 1. Camera Collimator 2. Scintillation Detector 3. Photomultiplier Tube 4. Positron Circuitry 5. Data Analysis Computer

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SPECT

4.1 Camera Collimator The first object that an emitted gamma photon encounters after exiting the body is the collimator. The collimator is a pattern of holes through gamma ray absorbing material, usually lead or tungsten that allows the projection of the gamma ray onto the detector crystal. The collimator achieves this by only allowing those gamma rays traveling along certain direction to reach the detector; this ensures that the position on the detector accurately depicts the originating location of the gamma ray.

4.2 Scintillation Detector In order to detect the gamma photon we use scintillation detectors. A Thallium-activated Sodium Iodide [NaI (TI)] detector crystal is generally used in Gamma cameras. This is due to this crystal’s optimal detection efficiency for the gamma ray energies of radionuclide emission common to Nuclear Medicine. A detector crystal may be circular or rectangular. It is typically 3/8” thick and has dimensions of 30-50 cm. A gamma ray photon interacts with the detector by means of the Photoelectric Effect or Compton Scattering with the iodide ions of the crystal. This interaction causes the release of electrons which in turn interact with the crystal lattice to produce light, in a process known as scintillation. Thus, a scintillation crystal is a material that has the ability to convert energy lost by radiations into pulses of light. The basic scintillation system consists of: 1.

Scintillator

2. Light Guide 3. Photo Detector

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SPECT

Fig. 4.2 Basic Scintillation System

4.3 Photomultiplier Tube Only a small amount of light is given off from the scintillation detector. Therefore, photomultiplier tubes are attached to the back of the crystal. At the face of a Photomultiplier tube (PMT) is a photocathode which, when stimulated by light photons, ejects electrons. The PMT is an instrument that detects and amplifies the electrons that are produced by the photocathode. For every 7 to 10 photons incident on the photocathode, only one electron is generated. This electron from the cathode is focused on a dynode which absorbs this electron and re-emits many more electrons. These new electrons are focused on the next dynode and the process is repeated over and over in an array of dynodes. At the base of the photomultiplier tube is an anode which attracts the final large cluster of electrons and converts them into an electrical pulse. Each gamma camera has several photomultiplier tubes arranged in a geometrical array. The typical camera has 37 to 91 PMT’s.

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SPECT

4.4 Positron Circuitry The positron logic circuits immediately follow the photomultiplier tube array and they receive the electrical impulses from the tubes in the summing matrix circuits (SMC). This allows the position circuits to determine where each scintillation event occurred in the detector crystal.

4.5

Data Analysis Computer Finally in order to deal with the incoming projection data and to

process it into a readable image of the 3D spatial distribution of activity with in the patient, a processing computer is used. The computer may use various different methods to reconstruct an image, such as filtered back projection or iterative construction.

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SPECT

5. SPECT IMAGE ACQUSITIONAND PROCESSING SINGLE photon emission computer tomography has its goal determination of the regional concentration of radionuclide with in a specific organ as a function of time. The introduction of radio isotope TC99m by Harpen ,which emits a single gamma ray photon of energy 140 KeV & has a half life of about six hours signaled a great step forward for SPECT since this photon is easily detected by gamma cameras . However, a critical engineering problem involving the collimation of this gamma rays prior to entering the gamma camera have to be solved before SPECT could establish itself as a viable imaging modality Single photon emission computed tomography requires collimation of gamma rays emitted by the radiopharmaceutical distribution within the body Collimators for SPECT imaging are typically made of lead. They are about 4 to 5 cms thick and 20 by 40 cm on its side. The collimators contain thousands of square, round or hexagonal parallel channels through which – gamma rays are allowed to pass. Typical low-energy collimators for SPECT weigh about 50 lbs, but high – energy models can weigh above over 200 lbs. Although quiet heavy, these collimators are placed directly on top of a very delicate single crystal of a NaI contain within every gamma camera. Any gamma camera so occupied with a collimator is called an angle camera after it is invented. Gamma rays traveling along a path that coincides with one of the collimator channels will pass through the collimator unabsorbed and interact with the NaI crystal creating light. Behind the crystal, a grid of photo multiplier tubes collects the light for processing. It is from the analysis of this light signals that SPECT

images are produced .Depending on the size of anger

cameras whole organs such as heart and liver can be imaged. Large anger cameras are capable of imaging the entire body and are used, for example, for bone scans.

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SPECT

For the gamma rays emitted by radiopharmaceuticals typical for SPECT, there are two important interactions with matter. The first involves scattering of the gamma ray off electrons in the atoms and molecules (DNA) within the body. This scattering process is called Compton scattering. Some Compton scattered photons are deflected outside the Anger cameras field of view and are lost to the detection process. The second interaction consists of a photon being absorbed by an atom in the body with an associated jump in energy level (or release) of an electron in the same atom. This process is called the photoelectric effect and was discovered for the interaction of photons with metals by Einstein, who received the Nobel Prize for this discovery. Both processes result in a loss or degradation of information about the distribution of the radiopharmaceutical within the body. The second process falls under the general medical imaging concept of attenuation and is an active research area. Attenuation results in a reduction in the number of photons reaching the Anger camera. The amount of attenuation experienced by any one photon depends on its path through the body and its energy. Photons which experience Compton scattering loose energy to the scatterer and are therefore more likely to be scattered additional times and eventually absorbed by the body or wide-angle scattered outside the camera’s field of view. In either case, the photon (and the information it carries about the distribution of the radiopharmaceutical in the body) is not going to be detected and is thus considered lost due to attenuation. At 14OKeV, Compton scattering is the most probable interaction of a gamma ray photon with water or body tissue. A much smaller percentage of photons are lost through the photoelectric interaction. It is possible for a Compton scattered photon to be scattered into the Anger camera’s field

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SPECT

of view. Such photons however do not carry directly useful information about the distribution of the radiopharmaceutical within the body since they do not indicate from where within the body they originated. As a result, the detection of scattered photons in SPECT leads to loss of image contrast and a technically inaccurate image. Acquiring and processing a SPECT image, when done correctly, involves compensating for and adjusting many physical and system parameters. A selection of these include: attenuation, scatter, uniformity and linearity of detector response, geometric spatial resolution and sensitivity of the collimator, intrinsic spatial resolution and sensitivity of the Anger camera, energy resolution of the electronics, system sensitivity, image truncation, mechanical shift of the camera or gantry, electronic shift, axis-of-rotation calibration, image noise, image slice thickness, reconstruction matrix size and filter, angular and liner sampling intervals, statistical variations in detected counts, changes in Anger camera field of view with distance from the source, and system dead time. Calibrating and monitoring many of these parameters fall under the general heading of Quality Control and are usually performed by a Certified Nuclear Medicine Technician or a medical physicist. Among this list, collimation has the greatest effect on determining SPECT system spatial resolution and sensitivity, where sensitivity relates to how many photons per second are detected. System resolution and sensitivity are the most important physical measures of how well a SPECT system performs. Improvement in these parameters is a constant goal of the SPECT researcher. Improvement in both of these parameters simultaneously is rarely achieved in practice.

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SPECT

5.1 COLLIMATION Since the time a patient spends in a Nuclear Medicine department relates directly to patient comfort, there exists pressure to perform all nuclear medicine scans within an acceptable time frame. For SPECT, this can result in relatively large statistical image noise due to a limited number of photons detected within the scan time. This fact does not hinder our current clinical ability to prognosticate the diseased state using SPECT, but does raise interesting research questions. For example, a typical Anger camera equipped with a low-energy collimator detects roughly one in every ten-thousand gamma ray photons emitted by the source in the absence of attenuation. This number depends on the type of collimator used. The system spatial resolution also depends on the type of collimator and the intrinsic (built in) resolution of the Anger camera. A typical modem Anger camera has an intrinsic resolution of three to nine millimeters. Independent of the collimator, system resolution cannot get any better than intrinsic resolution. The same ideas also apply to sensitivity: system sensitivity is always worse than - and at best equal to intrinsic sensitivity. A collimator with thousands of straight parallel lead channels is called a parallel-hole collimator, and has a geometric or collimator resolution that increases with distance from the gamma ray source. Geometric resolution can be made better (worse) by using smaller (larger) channels. The geometric sensitivity, however, is inversely related to geometric resolution, which means improving collimator resolution decreases collimator sensitivity, and vice versa. Of course, high resolution and great sensitivity are two paramount goals of SPECT. Therefore, the SPECT researcher must always consider this trade-off

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SPECT

when working on new collimator designs. There have been several collimator designs in the past ten years which optimized the resolution/sensitivity inverse relation for their particular design. Converging hole collimators, for example fan-beam and cone-beam have been built which improve the trade-off between resolution and sensitivity by increasing the amount of the Anger camera that is exposed to the radionudide source. This increases the number of counts which improves sensitivity. More modem collimator designs, such as half-cone beam and astigmatic, have also been conceived. Sensitivity has seen an overall improvement by the introduction of multi-camera SPECT systems. A typical triple-camera SPECT system equipped with ultra-high resolution parallel-hole collimators can achieve a resolution (measured at full-width half-maximum (FWHM) of from four to seven millimeters. Other types of collimators with only one or a few channels, called pin-hole collimators, have been designed to image small organs and human extremities, such as the wrist and thyroid gland, in addition to research animals such as rats.

5.2 COMPUTERS IN RADIOLOGY AND NUCLEAR MEDICINE Nuclear medicine relies on computers to acquire, store, process and transfer image information. The history of computers in radiology and nuclear medicine is however relatively short. In the 1960s and early 1970s, CT and digital subtraction angiography where introduced into clinical practice for the first time. Digital subtraction angiography used computers to digitally subtract from a standard angiogram the effects of surrounding soft-tissue and bone, thus improving the image for diagnosis. Computed tomography relied on computers to digitally reconstruct sectional data using various reconstruction algorithms such as filtered

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back projection. The work horse of the CT unit was the computer; without it CT was impossible. SPECT and MRI first began to appear in the late 1970s. Both of these new imaging modalities required a computer. In the case of MRI, the computer played a major role in controlling the gantry and related mechanical equipment. In the SPECT case, as in CT, image reconstruction had to be done by computer. Nuclear medicine’s reliance on computers also has its roots in high-energy particle physics and nuclear physics. Both of these disciplines rely on statistical analysis of large numbers of photon (or other particle) counts, collected and processed by a computer.

5.3 IMAGE ACQUISITION Nuclear medicine images can be acquired in digital format using a SPECT scanner. The distribution of radionudide in the patient’s body corresponds to the analog image. An analog image is one that has a continuous distribution of density representing the continuous distribution of radionuclide amassed in a particular organ. The gamma ray counts coming from the patient’s body are digitized and stored in the computer in an array or image matrix. Typical matrix sizes used in SPECT imaging are 256x256, 128x128, 128x64 or 64x64. The third dimension in the array corresponds to the number of transaxial, coronal or sagittal slices used to represent the organ being imaged. A typical SPECT scanner has a storage limit of 16 bits per pixel. Once a SPECT scan has been completed, the raw data image matrix is called projection data and is ready to be reconstructed. The reconstruction process puts the data in its final digital form ready for transmission to another computer system for display and physician analysis.

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SPECT

6. RECONSTRUCTION The most common algorithm used in the tomographic reconstruction of clinical data is the filtered back projection method. Other methods also exist. 1. Data Projection 2. Fourier Transform of Data 3. Data filtering 4. Inverse transform of the Data 5. Back projection

6.1

Data Projection As the SPECT camera rotates around a patient, it creates a series

of planar images called projections. At each stop, only photons moving perpendicular to the camera face pass through the collimator. As many of these photons originate from various depths in the patient, the result is an overlapping of all tracer emitting organs along a specified path. A SPECT study consists of many planar images acquired at various angles. The fig 6.1(a)displays a set of projections taken of a patient’s bone scan.

Fig. 6.1 (a) Data Projection of Bone Scan

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SPECT

After all projections are acquired, they are subdivided by taking all the projections for a single, thin slice of the patient at a time. All the projections for each slice are then ordered into an image called a ‘sinogram’ as shown in fig 6.1(b). It represents the projection of the tracer distribution in the body into a single slice on the camera at every angle of the acquisition.

Fig. 6.1 (b) sinogram The aim of reconstruction process is to retrieve the radiotracer spatial distribution from the projection data is shown in fig. 6.1 (c)

Fig. 6.1 (c) Reconstruction of Sinogram

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Seminar Report ’03 6.2

SPECT

Fourier Transform of Data If the projection sonogram data were reconstructed at this point,

artifacts would appear in the reconstructed images due to the nature of the subsequent back projection operation. Additionally, due to the random nature of the radioactivity. There is an inherent noise in the data that tends to make the reconstructed image rough. In order to account for both of these effects, it is necessary to filter the data. We can filter it directly in the projection space, which means that we convolute the data by some sort of smoothing kernel. Convolution is computationally intensive.

Convolution in tyhr

spatial domain is equivalent to a multiplication in the frequency domain. This means that any filtering done by the convolution operation in the normal spatial domain can be performed by a simple multiplication when transformed into the frequency domain. Thus we transform the projection data into the frequency space where by we can more efficiently filter the data.

6.3 Data filtering Once the data has been transformed to the frequency domain, it is then filtered in order to smooth out the statistical noise. There are many different filters available to filter the data and they all have slightly different characteristics. For instance, some will smooth very heavily so that there are not any sharp edges, and hence will degrade the final image resolution .other filters will maintain a high resolution while only smoothing slightly .some typical filters used are Hanning filter, Butter worth filter, Low pass cosine filter, ZWeiner filter etc .Regardless of the

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SPECT

filter used, the end result is to display a final image that is relatively free from noise and is pleasing to the eye. The fig. 6.3 depicts three objects reconstructed without a filter true (left), without a filter noisy (middle) and with a Hanning filter (right).

Fig. 6.3 Reconstruction of objects using Filters

6.4

Inverse transform of data As the newly smoothed data is now in the frequency domain, we

must transform it back into the spatial domain in order to get out the x, y, z information regarding spatial distribution. This is done in the same type of manner as the original transformation is done, expect we use what is called the one dimensional inverse Fourier transform. Data at this point is similar to the original fig. 6.4 (a) sonogram expect it is smoothed as shown in fig. 6.4 (b).

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SPECT

(a) inverse transform of the data

(b) Sinogram of inverse transform

Fig. 6.4

6.5 Back Projection The main reconstruction step involves a process known as ‘Back Projection’. As the original data was collected by only allowing photons emitted perpendicular to the camera face to enter the camera, back projection smears the camera bin data from the filtered sonogram back along the same lines from where the photon was emitted from. Regions where back projection lines from different angles intersect represent areas which contain higher concentration of radiopharmaceutical,

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SPECT

7. ADVANTAGES OF SPECT 1.

Better detailed resolution: superimposition of overlying structures is removed.

2.

Lesion contrast higher: small deep lesions may be seen as small differences

in

radiopharmaceutical

distribution

and

can

be

detected. Hence resolution is improved.

3.

Localization of defects is more precise and more clearly seen by the inexperienced eye.

4.

Extend and size of defects is better defined.

5.

Images free of background.

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SPECT

8. DISADVANTAGES OF SPECT 1. Since lead collimator is used, it introduces defects in scanning. Only 1out of 1000 photons emitted hits the detector and contributes to image reconstruction. 2. A blurring effect is caused due to the gamma particles penetrating the collimator walls and opaque objects. 3. Spatial resolution is limited 4. Attenuation compensation is not possible due to multiple scattering of electrons

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SPECT

9. SPECT APPLICATIONS 1.

Heart Imaging SPECT has been applied to the heart for myocardial perfusion

imaging. The following figure is a myocardial MIBI scan taken under stress conditions. Regions of the heart that are not being per fused will display as cooler regions.

2.

Brain Imaging This figure is a transverse SPECT image of the brain. The hot

spots present in the right posterior region are seen clearly using SPECT. SPECT examines cerebral function by documenting regional blood flow and metabolism. The SPECT and PET imaging modalities are especially valuable in brain imaging as they make it possible to visualize and quantify the density of different types of receptors and transporters. The accurate assessment of the density of receptors or transporters in the brain structure is quite challenging because of the small size of these structures.

3.

SPECT imaging

is specially used to differentiate between infarct

and ischemic. Infarct is an area of necrosis in the tissue or the organ resulting from obstruction of the local circulation by a thrombus or embolus. Ischemic is a condition of the localized anemia due to an obstructed circulation. Clinical studies indicate that SPECT is more accurate at detecting acute ischemia than CT scan.

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SPECT

4. Tumor detection SPECT can be used to detect tumors in cancer patients in the early stages itself. Using this slicing method, we can remove any interference from the surrounding area and detect disfuntionality of organs pretty easily. The radioactive chemicals will distribute through the body. The distributions can be traced and compared to that of a normal healthy body. Since this method is so precise, doctors can detect abnormalities in the early stages of disease development when it is more curable. SPECT has been proven alternative to PET in distinguishing recurrent brain tumor from radiation necrosis.

5. Bone Scans Bone scans are typically performed in order to assess bone growth and to look for brain tumors. The tumors are the dark areas seen in the picture below. The development of SPECT has enhanced the contrast resolution of bone scans by screening out overlying and underlying tissue. This results in increased detection and localization of small abnormalities especially in the spine, pelvis and knees. A bone scan typically costs about one third to half as much as a CT or MRI. 6. SPECT

is superior to other imaging modalities in detecting subtle

instances of Spondylolysis and assessing the degree of injury activity. SPECT is also used in diagnosing Alzheimer’s disease, for performing lung perfusion, abdominal and pelvic scanning and in diagnosing epilepsy. Radionuclide scans with increased imaging techniques such as SPECT have become safe well- established and highly effective diagnostic tools in sports medicine.

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SPECT

10. POSITRON EMISSION TOMOGRAPHY (PET) The distribution of activity in slices of organs can be obtained in a more accurate way using PET. In the simplest PET camera two modified sophisticated cameras called Anger cameras are placed on opposite sides of the patient. This increases the collection angle and reduces the collection times which are the limitations of SPECT .In PET, radiopharmaceuticals are labeled with positron emitting isotopes. A positron combines rather quickly with an electron. As a result the two gamma quanta are emitted almost in opposite directions .In PET scanners, rings of gamma ray of gamma ray detectors surrounding the patient are used. Each detector interacts electronically with the other detectors in the field of view. When a photon arrives within a short time frame, it is clear that a pair of quanta was generated and that these were created somewhere along the path between the detectors. Conventional PET tomography makes use of standard filtered back projection techniques used in computed tomography and SPECT. Three dimensional PET scanning has increased sensitivity but also noise. But since higher sensitivity permits lower radiation doses, the use is justified. PET is used to study the dynamic properties of biochemical processes. A large part of the biological system consists of hydrogen, carbon, nitrogen and oxygen. With the help of a cyclotron it is possible to produce short –lived isotopes of carbon, nitrogen and oxygen that emit positrons. Examples of these isotopes are 0-15, N-13, and C-11 with half – lives of 2, 10, and 13 minutes respectively. PET uses electron collimation instead of lead collimation. Attenuation correction can be more

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accurately done in case of PET. The resolution of PET is much better and uniform than SPECT.

11. COMPARISON OF PET AND SPECT

Fig. 11 SPECT imaging is inferior to PET because of attainable resolution and sensitivity. Different radionuclide is used for SPECT imaging that emits a single photon rather than positron emission as in PET. Because a single photon is emitted from the radio nuclides used for SPECT, a special lens known as a collimator is used to acquire the image data from multiple views around the body. The use of collimator results in a tremendous decrease in the detection efficiency as compared to PET. For Positron Emission Tomography, collimation is achieved naturally by the fact that a pair of detected photons (gamma rays) can be traced back to their origin since they travel along the same line after being produced. In PET, there might be as many as 500 detectors that could ‘see’ a PET isotope at any one time where as in SPECT; there may be only one or three collimators. New collimators are designed planar in one direction

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and concave in other which improves the spatial resolution and reduces the non – isotropic blur in SPECT , So that the resolution and sensitivity can be improved much to that of PET .,

Although SPECT imaging resolution is not that of PET, the availability of new SPECT radiopharmaceuticals, particularly for the brain and head, and the practical and economical aspects of SPECT instrumentation make this mode of emission tomography attractive for clinical studies of the brain. The cost of SPECT imaging is very low comparing to PET. PROS SPECT 1. Afford able Price

CONS 1. Limitation of spatial resolution

2. Large clinical practice 2. PET

Blurring

effect

with

higher

energy tracers 1. Good spatial resolution 1. Costly 2. Tracers required are of short half-lives,

hence

requires

cyclotrons and particle generators nearby itself

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12. CONCLUSION It is reasonable to speculate about a constant by perhaps a slower rate of increase of clinical applications of SPECT. It is safe to conclude that SPECT has reached the stage where it will be a valuable and also an unavoidable asset to the medical world. SPECT being a nuclear medicine imaging modality , it has all the advantages and disadvantages of nuclear medicine can be highly beneficial or dangerous on the application , so is SPECT .In spite of this , Today , nearly all cardiac patients receive a planar ECT or SPECT as part of their work-up to detect and stage coronary artery disease . Brain and Liver SPECT scans are also a leading application of SPECT. SPECT is used routinely to help diagnose and stage cancer, stroke, liver disease, lungs disease and a host of other physiological (functional) abnormalities.

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13. BIBLIOGRAPHY

1.

Xiaochuan Pan; Chien-Min Kao; Sidky, E.Y.; Yu Zou; Metz, C.E.; “/spl pi/-scheme short-scan SPECT and image reconstruction with nonuniform attenuation” Nuclear Science, IEEE Transactions on , Volume: 50 Issue: 1 , Feb. 2003 Page(s): 87 -96.

2.

R.S.Khandpur, ”Handbook of Biomedical Instrumentation”.

3.

Dr .M. Armugam, “Biomedical instrumentation”.

4.

Steve Webb, “Principles of Medical Imaging”.

5.

John.G.Webster,“Medical Instrumentation, Application and design”.

6.

www.nucmed.bidmc.harvard. Edu

7.

www.pumbed.com

8.

www.cti-pet.com

9.

www.healthimaging.com

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CONTENTS

1.

INTRODUCTION

2.

SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY 2

3.

THEORY AND INSTRUMENTATION

3

4.

THE GAMMA CAMERA

5

5.

SPECT IMAGE ACQUISITION AND PROCESSING

9

6.

RECONSTRUCTION

15

7.

ADVANTAGES OF SPECT

20

8.

DISADVANTAGES OF SPECT

21

9.

SPECT APPLICATION

22

10.

POSITRON EMISSION TOMOGRAPHY

24

11.

COMPARISON OF PET AND SPECT

25

12.

CONCLUSION

27

13.

BIBLIOGRAPHY

28

Dept. of AEI

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ABSTRACT SPECT, the acronym for Single Photon Emission Computed Tomography, is a nuclear medicine imaging modality, giving information about a patient’s specific organ or body system. The patient is injected with a radiopharmaceutical, which will emit Gamma rays. The radio activity is collected by an instrument called gamma camera and the image is reconstructed. SPECT is used to make three dimensional images of the heart, to perform brain studies and for skeletal scintigraphy.

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ACKNOWLEDGEMENT I extend my sincere gratitude towards

Prof . P.Sukumaran

Head of Department for giving us his invaluable knowledge and wonderful technical guidance

I express my thanks to Mr. Muhammed kutty our group tutor and also to our staff advisor Ms. Biji Paul for their kind co-operation and guidance for preparing and presenting this seminar.

I also thank all the other faculty members of AEI department and my friends for their help and support.

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