Scintillation Cameras

These are unique to scintillation cameras, known as Auger cameras, used in nuclear medicine studies. Approximately 19-91 PMTs are mounted on a Na(Tl) crystal used in the camera. These crystals are typically-thick. The number of PMTs, which are optically coupled to the back of the crystal, is determined by the size and shape of the crystal. A maximum amount of light will be received by the PMT nearest to the point of interaction compared with the other PMTs, which are positioned differently. The amount of light received in these PMTs is proportional to the solid angle subtended by the PMT. Therefore, X-Y-posi-tioning of the camera has to be controlled and known so that X-Y-coordinate of the y-Ray interaction can be assessed accurately. These data are stored in a computer and then processed or recorded on Polaroid or X-Ray films. 

Figure 13-6 Schematic diagram of a rotating triple-detector scintillation camera system for single photon emission computed tomography (SPECT) demonstrating a "cold" spot lesion in the brain on the sagittal view (open arrow).

A disadvantage of the coincidence scintillation cameras is that they have low sensitivity due to low detection efficiency of Nal(Tl) crystal for 511-keV photons, which results in a longer acquisition time. To improve the sensitivity, thicker detectors of sizes 1.6-2.5 cm have been used in some cameras, but even then, coincidence photopeak efficiency is only 3-4%. This increase in crystal thickness, however, compromises the spatial resolution of the system in SPECT mode. Fast electronics and pulse shaping are implemented in modern systems to improve the sensitivity. Also, there is a significant camera dead time and pulse pileups due to relatively increased single count rates in the absence of a collimator in PET mode. Low coincidence count rates due to low... 

Explain how SPECT scintillation cameras can be used in coincidence counting. Discuss the advantages and disadvantages of these cameras in coincidence counting. 

As stated in Chap. 2, in a PET scanner, block detectors are cut into small detectors and coupled with four PM tubes, which are arranged in arrays of rings. Each detector is connected in coincidence to as many as N/2 detectors, where N is the number of small detectors in the ring. So which two detectors detected a coincidence event within the time window must be determined. Pulses produced in PM tubes are used to determine the locations of the two detectors (Fig. 3.2). As in scintillation cameras, the position of each detector is estimated by a weighted centroid algorithm. This algorithm estimates... 

Modern PET scanners can have 10,000-35,000 detectors arranged in blocks and coupled to several hundred PM tubes. Because of the variations in the gain of PM tubes, location of the detector in the block, and the physical variation of the detector, the detection efficiency of a detector pair varies from pair to pair, resulting in nonuniformity of the raw data. This effect in dedicated PET systems is similar to that encountered in conventional scintillation cameras used for SPECT and PET studies. The method of correction for this effect is termed the normalization. Normalization of the acquired data is accomplished by exposing uniformly all detector pairs to a 511-keV photon source (e.g., 68Ge source), without a subject in the field of view. Data are collected for all detector pairs in both 2D and 3D modes, and normalization... 

Klopper JF, Hauser W, Atkins HL, Eckelman WC, Richards P (1972) Evaluation of Tc-99m-DTPA for the measurement of glomerular filtration rate, J Nucl Med 13 107-110 McAfee JG, Gagne G, Atkins HL, Kirchner PT, Reba RC, Blaufox MD, Smith EM (1979) Biological distribution and excretion of DTPA labeled with Tc-99m and In-111. J Nucl Med 20 1273-1278 Nielsen SP, Moller ML, Trap-Jensen J (1977) Tc-99m-DTPA scintillation-camera renography a new method for estimation of single-kidney function, J Nucl Med 18 112-117 O Reilly PH (1992) Diuresis renography. Recent advances and recommended protocols. Br J Urol 69 113-120... 

Scintillation Camera Data Processing. Data were recorded continuously on 9-track 800-bytes per inch tape, temporarily stored on disk, and analyzed to determine individual catheter count rates as a function of time. 

Figure 9.13.C shows the gamma scintillation camera, gamma camera, originally developed by Anger. It consists of a two-dimensional array of 40 - 100 PMTs (often hexagonally formed for tight stacking) viewing a large flat Nal(Tl) crystal of 400 mm diameter and 5-10 mm thick, which is located behind a lead collimator containing numerous holes. Typical hole size is 2 - 3 mm diameter and 40 mm l gth. Collimator dimensions (Fig. 9.13.D) depend on the E for is 0.2 - 0.3 mm.

G. H. Simmons, The Scintillation Camera, The Society of Nuclear Medicine, New York, 1988. 

Since fatty acids are the primary substrate for aerobic metabolism within the heart, they are also of interest as potentially useful tracers of myocardial perfusion (12-18). This class of compounds labeled with the positron emitter is being used with specially designed positron imaging (ECT) systems to quantitatively measure the regional distribution of myocardial blood flow in three dimensions (12,13,14). Carbon-11 labeled palmitic acid is also being evaluated as a tracer for studies of myocardial metabolism. Likewise, the o-iodofatty acids, which are structural analogs of the physiologic substrates, have been shown to be taken up by myocardial tissue in proportion to blood flow (15). Iodine-123 labeled 16-iodo-9-hexadecenoic acid (18,17) and 17-iodo-heptadeca-noic acid (18) have been used in conjunction with conventional scintillation cameras for in vivo studies in humans. In all cases with this class of compounds, turnover of the label within the tissue is related to some aspect of metabolism (17,18). 

Sobel et al. have published a series of reports on the use of labeled palmitic acid for metabolic studies using ECT techniques in animals and humans (12,13,14,57 58 59). Robinson et al. (16,17), Machulla et al. (18), and a few other investigators, have demonstrated the use of labeled with for perfusion studies and limited metabolic applications using conventional scintillation camera imaging systems. Myocardial uptake of similar compounds labeled with F and have also been reported (60,61,62). The many attempts... 

Hal s greatest contribution was to replace the rectilinear scanners with the scintillation camera (Fig. 7.5.) invented in 1957, and perfected in the 1960s and 1970s. The invention of the Anger camera led to the birth of nuclear cardiology, which accounts for more than half of all nuclear medicine imaging studies in the US today. 

Fig. 7.S Hal Anger, exhibiting the first scintillation camera at a meeting of the Society of Nuclear Medicine.

Hal enlisted the help of a physician, Alex Gottshalk, who came to the Donner Lab in July, 1962. By 1963, Hal and Alex described the Localization of Brain Tumors with the Positron Scintillation Camera (J Nuclear Medicine 4 326-330,1963). This represented the first clinical use of the positron scintillation camera. 

At the same meeting, Gottshalk and Anger presented a talk on Diagnostic Uses of the Scintillation Camera. They used the single photon camera with " Hg Neohydrin and Hippuran. The camera made dynamic studies possible. 

Bill recognized immediately the importance of the invention of the scintillation camera, and persuaded Professor Charles Doan, head of the Department of Internal Medicine at Ohio State, to place an order for the first commercial version. This camera was to be built by a new company. Nuclear Chicago, under the leadership of John Kuranz, President. The company was founded in 1947 by John Kuranz and others from the nuclear reactor laboratory of Em-ico Fermi at the University of Chicago. By the early 1970s, Ohio-Nudear of Solon, Ohio, as well as Picker Medical and General Electric, were also providing gamma cameras to hospitals. 

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