That is, it is either not functioning or has a substantially lower sensitivity than the other detectors. The term blank scan, derived from the first of these 2 approaches, reflects the absence of any material in the FOV; the term is still often applied to the latter approach, even though it involves placing an object (i.e., the 68Ge source) in the FOV. 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 CTDI is the basic radiation dose parameter in CT and is defined as the integral under the exposure or absorbed dose profile along the patient's longitudinal axis for a single tomographic image (2527). Differential uniformity (DU) is the maximum value of the expression on the right side of Equation 5 determined for every 5-pixel segment in every row and column of the flood image. (A) Unnormalized (i.e., uncorrected) image has obvious artifacts attributable to differences in sensitivities between direct and cross planes and presence of separate rings of block detectors. They are staggered (offset) 1 mm apart in longitudinal direction. -Camera uniformity may be evaluated either intrinsically (i.e., without collimation) or extrinsically (i.e., with collimation) (Fig. 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. (B) Phantom (NEMA IEC Body Phantom; Data Spectrum Corp.) with multiple fillable spheres and cylindric insert that can be filled with polystyrene to provide minimally attenuating material, simulating lung in otherwise uniform water-filled volume. 12). For each source, the measured activity on each scale and its current actual activity should agree within 10%. These parameters should be evaluated using a clinically routine set of scan parameters (i.e., kVp, mAs, pitch, etc.). These detectors have inherently better energy resolution that scintillators . CT.Radionuclidecalibrator.Thyroiduptakeprobe. Chapter 02. 7). (Though seldom used in practice, sheet source that may be filled with different radionuclides and used to evaluate extrinsic uniformity is also shown in photograph.) All position displays on the gantry and computer console and all alignment lasers should likewise be visually inspected. Chapter 08. Chapter 09. For this purpose, a registration phantom having volume markers with dimensions at least 3 times the SPECT or PET FWHM spatial resolution (to eliminate underestimation of activity due to partial-volume averaging) is preferred (Fig. Iterative algorithms yield progressively refined estimates of the activity distribution, rather than directly calculating the distribution, by maximizing or minimizing some target function. Ionization chambers actually measure exposure, which is then converted to absorbed dose using the f factor discussed earlier. High-contrast contrast resolution. Imaging in Nuclear Medicine deals with photons ~140-511 keV . Chapter 05. Such display allows operator to quickly and easily discern out-of-tolerance results, displayed with grossly different (i.e., lower) intensity than within-tolerance results. 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). 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. Nuclear Medicine - PET/CT 1. Over that time, which is equivalent to 12 half-lives of 99mTc, the activity decays to about 11 MBq. Radionuclide Therapy Many nuclear medicine facilities have their survey meters calibrated by the institutional radiation safety office or by a commercial calibration laboratory. 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). Journal of Nuclear Medicine Technology March 2001, 29 (1) 4-11; Article Figures & Data Info & Metrics PDF Abstract Objective: The purpose of this paper is to introduce technologists to the basic principles of PET imaging and to the instrumentation used to acquire PET data. They are designed, as an additional training tool to assist in the better presentation of the content of each chapter. 4B). Level II Minimum of two years' experience as a Nuclear Medicine technologist. 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). Boxes indicate pertinent ROIs for different analyses. In addition to an outdated uniformity correction table, the following are other causes of -camera nonuniformity (Fig. (B) Appearance of such artifact (arrow) in clinical SPECT image, transverse image from 99mTc-sulfur colloid liverspleen study. The routine QC tests for well counters include checks of the photopeak energy window (i.e., energy peaking) if the counter is equipped with an MCA and of background, constancy, and efficiency (or sensitivity). If the mechanical and electronic CORs are aligned, the pixel location of the projection of the COR onto the projection image matrix will be the same for all projection images, and for all such images the counts in each pixel will then be projected across the appropriate row of pixels in the tomographic image matrix. Duties and Responsibilities of this Level. Nuclear Medicine Image Display, Chapter 15. 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. Technologists are members of the team required to implement diagnostic imaging in nuclear medicine (NM). For a material X with linear attenuation coefficient X, the corresponding HU value is therefore ([X water]/[water air]) 1,000, where water and air are the linear attenuation coefficients of water and air, respectively. This article should be particularly useful for residents, fellows, and other trainees in nuclear medicine, nuclear cardiology, and radiology. Thus, a long-lived reference source or set of reference sources (such as 57Co, 133Ba, 68Ge, or 127Cs [Table 1]) should be available for daily checks of counting-rate constancy; a marked change (e.g., 10%) in the net counting rate from one day to the next may indicate an inappropriate energy window setting or some other technical problem. View Full Size | | Download Slide (.ppt) + + Nuclear medicine uses radioactive compounds called radiopharmaceuticals or radiotracers that interrogate physiologic or pathologic processes at a molecular level and provide targeted therapy for a variety of diseases. Historically, organ uptake probes have been used almost exclusively for measuring thyroid uptake and are thus generally known as thyroid uptake probes. CT scanners have been in widespread clinical use long before their incorporation into multimodality devices (i.e., SPECT/CT and PET/CT scanners), and detailed protocols for acceptance testing and evaluation of numerous CT performance parameters are well established (1,2,22). At installation and after service of a dose calibrator, its geometry (position and volume)-dependent response for 99mTc must be measured and volume (from 2 to 25 mL)-dependent correction factors relative to the standard volume (e.g., 10 mL) derived. Spatial resolution. Such standards are commercially available in various activities and geometries, depending on the application. The comprehensive look at -camera image production and at . 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). The higher the image contrast, the larger the difference between the water and the acrylic CT numbers within this ROI and the higher the SD of the CT number. (A) Sinogram (i.e., histogram) presentation of emission tomography (i.e., SPECT or PET) data. Multimodality (i.e., SPECT/CT and PET/CT) devices are still fairly new, and so QC procedures for checking the accuracy of image registration and of CT-based attenuation corrections are not yet well established. (B) Display for blank scan in which coincidence counting rate, singles counting rate, and dead-time results for 1 block detector are out of tolerance, indicated by black areas (arrows) in respective displays. It should be particularly useful for residents, fellows, and other trainees in nuclear medicine, nuclear cardiology, and radiology. Additional protocols for acceptance testing of PET and PET/CT scanners are currently being developed by Task Group 126 of the AAPM and by the International Atomic Energy Agency, respectively. Chapter 15. 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. Isotope-specific radionuclide counting or imaging with a scintillation detector commonly is done using a 20% photopeak energy window, equivalent to an energy range of E 10% (i.e., 0.91.1 E), where E is the x- or -ray energy of the radionuclide. The maximum likelihood expectation maximization (MLEM) algorithm is based on maximizing the logarithm of a Poisson likelihood target function. Chapter 18. The current article is a brief overview of such routine QC procedures for current nuclear medicine instrumentation, including the survey meter, dose calibrator, well counter, intraoperative probe, organ ("thyroid") uptake probe, -camera, SPECT and SPECT/CT scanner, and PET and PET/CT scanner. Each chapter concludes with a small number of references and suggested additional readings. Intrinsically, point source is placed at least 3, and preferably 5, crystal dimensions from and centered over uncollimated detector to provide uniform photon flux (left). Section shown in B includes polystyrene membrane with series of holes (10, 7.5, 5, 3, and 1 mm in diameter) that also fill with water when phantom is filled, providing low contrast between holes and polystyrene. IUs of 3% or better are routinely obtained for modern -cameras. Nuclear Medicine Image Display 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 energy resolution (expressed as the percentage full width at half maximum [FWHM] of the photopeak) should be checked at least quarterly using a reference-source radionuclide such as 57Co. 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. Linearity (i.e., CT number accuracy) is checked by verifying that the mean CT number (in HU) in a 10 10 mm ROI in air, water, and acrylic (the dotted squares in Fig. If not, Equation 10 must be appropriately adjusted:Eq. 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. Assuming the operator has received the appropriate system-ready message, the daily QC procedures are then performed (12). 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). Position Overview: The Nuclear Medicine Technologist is responsible for performing routine and specialized nuclear medicine procedures and examinations for radiological diagnosis. The reference-source activity should be sufficient to yield an exposure rate of 1,000 mR/h under the foregoing measurement conditions, and the exposure rates should be measured on each scale and, by appropriate adjustment of the sourcemeter distance, at 2 readings (20% and 80% of the maximum) on each scale. However, for 3-dimensional PET, the contribution of and correction for scatter with such a large-volume source are nontrivial. Enter multiple addresses on separate lines or separate them with commas. 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. In rotating--camera SPECT, the location of the projection of the COR on the projection image matrix must be independent of the projection-image angle (Fig. Solid-state detectors use a nonair-equivalent crystal as the detection medium and thus cannot measure exposure rates; they can measure only counting rates. 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. Phantoms adaptable to evaluation of accuracy of multimodality image registration. The red boxes in Figure 12C illustrate the 5 5 cm ROIs used for these analyses, as discussed earlier. For technical information on the instrumentation covered in this article, including further details on QC procedures, additional reading is recommended (1017). The IAEA has recently published the Nuclear Medicine Physics Handbook, which is intended for teachers, students and residents involved in medical physics programmes, and aspiring to serve as primary text for academic education and clinical training of Nuclear Medicine Medical Physicists in the IAEA Member States. 4A). 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. Nuclear medicine uses radionuclides in medicine for diagnosis, staging of disease, therapy and monitoring the response of a disease process. Graham et al. 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. In addition to daily battery and background checks (as performed for survey meters), QC tests of intraoperative probes should include a daily bias check for both the primary and any back-up battery to verify that bias voltage (or high voltage) is within the acceptable range. Additional training material, in the form of teaching slides, has been developed for each chapter of the handbook. The calibration factor, CF, is derived by the well-counter (or absolute activity) calibration: scanning a calibrated source, that is, a volume source (often a cylinder 20 cm in diameter by 20 cm in length), with a uniform, well-defined activity concentration at the time of the scan. 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). Survey meters should be calibratedthat is, checked for accuracyusing suitable long-lived reference sources at installation, annually, and after any repair. The OSEM algorithm, which is a modified version of the MLEM algorithm because the target is still maximization of the log likelihood function, converges more rapidly than MLEM and is now the most widely used iterative reconstruction method in PET and SPECT. 10). Even though cracks are grossly imperceptible, artifacts produced are dramatic. Iterative reconstruction algorithms allow incorporation of realistic modeling of the data-acquisition process (including effects of attenuation and of scatter), modeling of statistical noise, and inclusion of pertinent a priori information (e.g., only nonnegative count values). Quantitative Nuclear Medicine, Chapter 20. Since Nuclear Medicine diagnostic applications are growing fast, room temperature semiconductor detectors such CdTe and CdZnTe either in the form of single detectors or as segmented monolithic detectors have been investigated aiming to replace the NaI scintillator. Setup for measurement of CT radiation exposures using ionization chamber and 32-cm-diameter acrylic torso (body) phantom. As a result, the accuracy of the CT-based attenuation corrections cannot be meaningfully assessed. The MDA should be evaluated at least annually. At installation, therefore, the calibrated sample of each radionuclide (e.g., 99mTc) and its surrogate (e.g., 57Co) should be counted using the photopeak energy window (e.g., 126154 keV for 99mTc) and the respective efficiencies determined. All rights reserved. The integral uniformity (IU) is defined by the following equation:Eq. The accuracy of the CT number of water and image noise can also be evaluated using the same ROIs. Finally, as with all electromechanical devices, intraoperative probes, organ uptake probes, -cameras, SPECT and SPECT/CT scanners, and PET and PET/CT scanners should be inspected regularly for frayed wires and broken or otherwise damaged electrical insulation, loose electrical or mechanical connections (including missing or visibly loose screws, nuts, or bolts), and dents, sharp edges, or other physical damage. * NOTE: FOR CE CREDIT, YOU CAN ACCESS THIS ACTIVITY THROUGH THE SNM WEB SITE (http://www.snm.org/ce_online) THROUGH JULY 2009. 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