Because tomographic image reconstruction propagates and, in fact, may amplify the effects of nonuniformities, uniformity of -camera response is another consideration in obtaining high-quality SPECT images. Importantly, the certified activities of such reference sources must be traceable to the National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards. (Courtesy of Dr. Barbara Binkert, New York Presbyterian Hospital, New York, NY.) (B) Uncoupling of PMT from crystal, resulting in loss of all or part of light signal in resulting air gap between PMT entrance window and crystal. * Oversees the review of radiation human-use clinical research protocols to ensure proper disclosure of radiation exposure and ensure compliance with the hospital policies and local and federal regulations. If necessary, the activity should be adjusted to yield a measured counting rate of no greater than 25,000 cycles per second (cps), to avoid dead-time counting losses and counting-raterelated image degradation. Functional Measurements in Nuclear Medicine 1where Ao is the activity (in MBq) of the reference source at calibration, is the physical decay constant (in /d) of the radionuclide comprising the reference source, t is the time interval (in d) between the calibration of the reference source and the current measurement, is the specific -ray constant (in mR/h/cm2/MBq) of the radionuclide comprising the reference source, and d is the distance (in cm) between the reference source and the meter. Chapter 14. As an ionization chamber, the cutie-pie has an electron signal that depends on the energy of the detected x- or -rays and is therefore directly related to the exposure for all radionuclides. Two-dimensional PET sinograms and reconstructed transverse images through hot-sphere 18F-filled phantom: sinogram without any perceptible artifacts (A) and corresponding transverse image (B); sinogram with blank diagonal band, suggestive of faulty detector block (C) and corresponding transverse image (D). If LORT is the total number of LORs and a total of NT events is acquired in the normalization scan, the average number of counts per LOR, , is simply:Eq. Instrumentation | Nuclear Medicine and Molecular Imaging | Stanford Medicine. (A) Severe ring, or bull's-eye, artifact in transverse SPECT image through 20-cm diameter 99mTc-filled cylinder phantom resulting from gross -camera nonuniformity (i.e., IU 10%). Management of Therapy Patients Additional training material, in the form of teaching slides, has been developed for each chapter of the handbook. CT.Radionuclidecalibrator.Thyroiduptakeprobe. Coordinate and participate in a variety of technical procedures to include in vivo and in vitro studies; operate radiation detection and measurement instrumentation including stationary imaging devices, scintillation gamma and apparatus for in vitro counting. Aside from the counting geometry and sensitivity, uptake probes and well counters actually have much in common, and the QC procedureschecks of the photopeak energy window, background, constancy, and efficiencyare therefore analogous. The correction tables include uniformity; energy, which essentially corrects the -camera image for nonuniformities related to differences among the local-energy spectra; or linearity, which is largely a geometric correction, correcting the image for nonuniformities related to the position-dependent differences in the efficiency of light collection from the scintillation crystal by the PMTs (i.e., higher efficiency directly beneath the PMTs vs. lower efficiency between the PMTs). In addition to the QC procedures for -camera imaging listed earlier, rotating--camera SPECT requires specific QC tests. Chapter 20. In addition to the these daily checks of CT performance, monthly or at least quarterly evaluations of laser alignment, image slice thickness, spatial resolution, linearity (i.e., CT number accuracy), and high- and low-contrast contrast resolution are needed. Chapter 10. 5A). These QC tests and calibrations apply to both PET-only scanners and the PET subsystem of PET/CT scanners. The CTDIw thus reflects the mean absorbed dose over the transverse (x and y) dimensions of such a phantom and is an approximation of the average radiation dose to the cross-section of a patient. This fillable acrylic phantom is 22 cm in diameter by 19 cm in length and includes plain section for evaluation of tomographic uniformity (C), section containing empty (cold) spheres ranging from 9.5 to 31.8 mm in diameter for evaluation of cold-sphere contrast (D), and section containing solid (cold) rods ranging from 3.2 to 11.1 mm in diameter for evaluation of reconstructed spatial resolution (E). Appendix I. Artefacts and Trouble-Shooting. Such a semiquantitative (i.e., visual) assessment is faster and more convenient than actual measurement of spatial resolution of the FWHM of the line-spread function. Because the line cavities in each of the 2 slice-thickness measurement components of the insert are staggered (offset) 1 mm apart in the longitudinal direction (Figs. Non-Imaging Detectors and Counters, Chapter 11. NUCLEAR MEDICINE. The procedures described and their respective frequencies are presented only as general guidelines. These QC tests and calibrations apply to the CT subsystems of both SPECT/CT and PET/CT scanners. In this way, long-term trends in instrument performance, often imperceptible from one day to the next, may become apparent. In practice, however, less time-consuming and less rigorous procedures often suffice for day-to-day QC. 12B), and is expressed as the percentage difference between the CT numbers (in HU) in the water and the polystyrene membrane ROIs. Chapter 09. Although energy resolution per se is often not routinely evaluated, the energy spectrum for each radionuclide used clinically should be checked at least once a day and ideally for each patient to verify that the photopeak is centered in the photopeak energy windows currently set; Figure 4A illustrates the type of suboptimal image that may result with a mistuned (detuned) -camera. 12A and 12D). 3where is the gross (i.e., total) counting rate of the radionuclide source, is the background counting rate, Ao is the activity (in Bq) of the radionuclide source at calibration, is the physical decay constant of the radionuclide comprising the reference source, and t is the time interval between the calibration of the radionuclide source and the current measurement. Statistics for Radiation Measurements Each marker, for example, should be fillable with a solution containing both an image-able radionuclide such as 99mTc (for SPECT) or 18F (for PET) and a radioopaque contrast agent such as iohexol (Omnipaque; GE Healthcare). Measurements of the CTDI100 (p) and CTDI100 (c) are typically performed using ionization chambers or thermoluminescent dosimeters positioned in a commercially available soft-tissueequivalent acrylic phantom, cylindric in shape and either 16 or 32 cm in diameter, approximating an adult head or torso (body), respectively (Fig. (B) Appearance of such artifact (arrow) in clinical SPECT image, transverse image from 99mTc-sulfur colloid liverspleen study. Devices for Evaluating Imaging Systems PPT - Nuclear Medicine Instrumentation PowerPoint Presentation, free download - ID:9455563 Create Presentation Download Presentation Download 1 / 38 Nuclear Medicine Instrumentation 64 Views Download Presentation Nuclear Medicine Instrumentation. NOTE: We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail. Slice thickness. Because intraoperative probes may not provide a display of the energy spectrum, one may not be able to visually check that the probe is properly peaked, that is, that the photopeak coincides with the preset photopeak energy window. Nuclear medicine is a medical specialty that uses radioactive tracers (radiopharmaceuticals) to assess bodily functions and to diagnose and treat disease. In addition to an outdated uniformity correction table, the following are other causes of -camera nonuniformity (Fig. 11), even optimally performing PET scanners exhibit some further nonuniformity of response. Duties and Responsibilities of this Level. 11where Patient and Standard are the branching ratios of the positron-emitting isotope administered to a patient and added to the source, respectively. Thus, if P and 1 P represent the probabilities that random variations in a set of measurements from a Poisson distribution are, respectively, greater than or equal to or smaller than the calculated 2 value, a P value (or 1 P value) of 0.5 indicates the calculated 2 value is in the middle of the range expected for a Poisson distribution. Such tests of multimodality image registration should be performed at least monthly. It is generally helpful to track the results of QC tests longitudinally (e.g., in the form of a graph of the numeric result vs. date of the test). No potential conflict of interest relevant to this article was reported. Specially designed cameras allow doctors to track the path of these radioactive tracers. However, for 3-dimensional PET, the contribution of and correction for scatter with such a large-volume source are nontrivial. Tomographic uniformity should therefore be evaluated by high-count imaging of a 99mTc-filled cylinder source (at least 20 cm in diameter by 20 cm in length) and visually inspecting the resulting reconstructed images for the absence of perceptible nonuniformity artifacts; this should be done monthly. Fortunately, in contrast to uniformity correction table and, to lesser extent, energy correction table, linearity correction table rarely needs to be updated once -camera is installed; if updating becomes necessary, it is almost always done by field-service personnel of manufacturer, not by end-user. (Courtesy of Dr. Sadek Nehmeh, Memorial Sloan-Kettering Cancer Center, New York, NY.). That is, it is either not functioning or has a substantially lower sensitivity than the other detectors. Long-Lived Radionuclides Comprising Reference Sources for Instrumentation QC. 7. 7C) and may be evaluated with either a 18F-filled cylinder phantom or a 68Ge cylinder source. Level II Minimum of two years' experience as a Nuclear Medicine technologist. As a result, the accuracy of the CT-based attenuation corrections cannot be meaningfully assessed. Nuclear Medicine and Molecular Imaging Radiology. Whole-body target expression can be quantified and used for predicting therapy response. If the source is small (compared with the mean free path of its emitted x- and -rays within the material comprising the source) and the distance between the source and meter large (compared with the dimensions of the source), then a point-source geometry is approximated and the expected exposure rate (in mR/h), , in air is given by the inverse-square law:Eq. High-contrast contrast resolution. Dowload the Powerpoint version of the slides, Chapter 01. Specifically, the residual, otherwise imperceptible nonuniformity of a -camera with an IU and a DU within tolerance (i.e., <5%) on the basis of the daily flood image may produce significant ring, or bull's-eye, artifacts in tomographic images (Fig. For the quarterly check of linearity by the so-called decay method, one begins with a high-activity (37 GBq), independently calibrated 99mTc source and assays its activity at 12-h intervals over 3 consecutive days. 13). Computers in Nuclear Medicine It is also used in the basic sciences such as biology, in drug discovery and in pre-clinical medicine. 12C), 5-cm-diameter circular or 5 5 cm ROIs (1 at the center and 4 at the periphery, at approximately the 12-, 3-, 6-, and 9-o'clock positions) are placed on the image and the mean CT numbers (in Hounsfield units [HU] (23)) compared between the central and each of the peripheral ROIs; the maximum difference should not exceed 5 HU. (B) Appropriate normalization virtually eliminates these and other artifacts related to nonuniformity of scanner response. For the accuracy test (also sometimes known as the energy linearity test), NIST-traceable reference sources of at least 2 of the radioisotopes listed in Table 1 are separately placed in the dose calibrator and the activity reading on each scale recorded. The PET scanner well-counter calibration should be created or updated at installation, after major service, or otherwise at least annually. Conversely, a P value of less than 0.01 or greater than 0.99, respectively, indicates that there is only a 1% chance that a Poisson distribution would yield an 2 value as large as or as small as that actually calculated. Thank you for your interest in spreading the word on Journal of Nuclear Medicine. Chapter 19. (A) COR misalignment and resulting image-blurring artifacts in rotating--camera SPECT. Chapter 07. Quantitative Nuclear Medicine, Chapter 20. Nuclear Medicine Imaging Devices, Chapter 12. Because such reference sources are long-lived, a single standard may be used for months to years, avoiding the need to prepare sources on a daily or weekly basis and thereby avoiding possible inaccuracies in dispensing activity as well as the possibility of radioactive contamination. 8C vs. 8B) or band (Fig. Using such a phantom, so-called cold-sphere contrast may be evaluated on the basis of the minimum counts in sphere i and the mean counts in the plain transverse section closest to the sections through the spheres (Figs. Among the 10,00020,000 detector elements in a modern ring scanner, slight variations among the detector elements in thickness, light emission properties, electronics performance, and so on result in slightly different line-of-response (LOR) counting rates for the same activity. The radionuclide source should be a precisely calibrated sample (37 kBq in 1 mL) prepared by appropriate dilution and careful aliquoting of an activity of that radionuclide sufficiently large to be accurately assayed in a dose calibrator. The far more rigorous and more extensive acceptance-testing procedures performed for -cameras, SPECT and SPECT/CT scanners, and PET and PET/CT scanners are beyond the scope of this article, which is not intended to supersede or replace manufacturer-recommended acceptance-testing, QC, and preventive-maintenance procedures. The lead bars in at least the 2 coarsest quadrants (i.e., with the 3- and 4-mm-wide bars) should be visually resolvable. QC tests of survey meters generally include a daily battery check, with a display indicating whether the voltage supplied by the battery is within the acceptable operating range. For all readings, the expected and measured exposure rates should agree within 10%. In either case, the PMT gain, crystal (detector) map, or photopeak energy window of the affected detector block may need to be adjusted (11,16), the normalization updated, or a faulty hardware component repaired or replaced. Such counting results should be expressed in activity (e.g., Ci), using the appropriate isotope-specific calibration factor (Ci/cpm). According to information published by GE Healthcare (24), this difference should agree within 0.1% (1 HU) with the benchmark, or reference, low-contrast contrast resolution of the scanner, established at the time of its installation. Spatial resolution and spatial linearity, in practice, are generally assessed semiquantitatively using some sort of resolution phantom (or mask) such as the 4-quadrant bar phantom (Fig. Chapter 01. For each QC test performed, the following data, as well as the initials or signature of the individual performing the test, should be recorded on a structured and suitably annotated form: the test performed; the date and time of the test; the make, model, and serial number of the device tested; the make, model, and serial number of any reference sources used; the results of the test; and a notation indicating if the test result was or was not acceptable (i.e., was or was not within the specified tolerance range). Although the shield method is much faster than the decay method for checking linearity (taking minutes instead of days), an initial decay-based calibration of the set of sleeves is recommended to accurately determine the actual decay equivalence of each shield. One approach to evaluating the daily blank scan is simple visual inspection of its (2-dimensional) sinograms (Fig. An alternative approach to checking linearity is the so-called shield method, in which lead sleeves of increasing thickness are placed in the dose calibrator with a 99mTc source (Fig. Misalignment as small as 3.2 mm (or 0.5 pixel for 64 64 image matrix) can produce perceptible blurring in SPECT images, with blurring substantially worse for misalignment of 6.4 mm (1 pixel). The technical editors and authors, selected for their experience and in recognition of their contributions to the field, were drawn from around the world and, thus, this book represents a truly international collaboration. Sources of -camera nonuniformity. The PET scanner normalization should be created or updated at installation, after major service, whenever deteriorating image quality suggests a new normalization is required, or otherwise at least annually. 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