ASNC clinical update
Collimator integrity

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Overview

Collimators constitute a critical component of the imaging system and have a direct effect on image quality. Therefore ensuring collimator integrity is vital for quality assurance in nuclear cardiology. Routine checks should be performed on all collimators in clinical use (Table 1). Extrinsic flood images provide an assessment of collimator uniformity and should be acquired at regular intervals. Technologists must be conscious of unintended damage to the collimators and other related issues

Camera uniformity: Calibration

The gamma camera sensitivity must be sufficiently uniform across the field of view to avoid nonuniformity artifacts in images. There are 2 components to gamma camera uniformity, arising from the detector itself and from the collimator. Intrinsic uniformity refers to the spatial-dependent sensitivity of the camera without a collimator. Extrinsic uniformity refers to the spatial-dependent sensitivity of the camera with a specific collimator mounted in place.

Gamma cameras are calibrated to ensure

Camera uniformity: Quality assurance

On a daily basis, flood images are acquired and inspected to ensure that substantial changes to camera uniformity have not occurred. For example, such changes may be caused by a malfunctioning photomultiplier tube, a malfunctioning electronic circuit, or a significant environmental change such as a power surge or temperature change. It is not practical to acquire high-count flood images on a daily basis. Instead, lower-count flood images are acquired, typically 3 to 5 million counts, which are

Collimator damage and camera uniformity

The collimator covers the front surface of the gamma camera and is vulnerable to impact. Damage to the collimator may occur if an external object collides with the collimator surface, or vice versa. Collimator damage may occur knowingly or unknowingly to the technologist (eg, after hours by the cleaning staff). Collimators are made of lead, which is a soft metal that may be deformed or dented relatively easily. In addition, most collimators are constructed from lead foil sheets bonded together

Mechanical integrity guidelines

On a daily basis, technologists should inspect collimators for visual signs of surface damage, such as marks or indentations that would arise from an object impacting the collimator. Patient safety mechanisms (touch pads/contact sensors) should be tested routinely for proper operation. During use, technologists should take care to avoid mechanical damage to the collimators from collisions with other equipment.

When changing collimators, the latching mechanism should be observed to ensure that

Camera uniformity guidelines

Acquiring an extrinsic flood image allows collimator uniformity to be evaluated, whereas an intrinsic flood image does not provide this information. The extrinsic flood image should be inspected in combination with the intrinsic flood image to distinguish collimator-related nonuniformity from detector-related nonuniformity. In addition, inspecting extrinsic flood images acquired with the uniformity correction tables disabled provides further information as to the integrity of the collimator,

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Prepared by the American Society of Nuclear Cardiology (ASNC) Quality Assurance Subcommittee for Laboratory Quality.

Reviewed by members of the ASNC Quality Assurance Committee: Edward P. Ficaro, PhD, Chair; Olakunle O. Akinboboye, MBBS, MPH, MBA; Elias H. Botvinick, MD; Ji Chen, PhD; Keith B. Churchwell, MD; C. David Cooke, MSEE; Roger D. Des Prez, MD; Guido Germano, PhD; Richard A. Goldstein, MD, MBA; Christopher L. Hansen, MD; Robert C. Hendel, MD; Milena J. Henzlova, MD; Brad J. Kemp, PhD; Benjamin D. McCallister, MD; Vahini V. Naidoo, MD; Patty Reames, CNMT, RT(R), NCT; Raymond R. Russell III, MD, PhD; Albert J. Sinusas, MD; Massimiliano Szulc, PhD; Peter L. Tilkemeier, MD; Yvonne J. Weaver, MD; and David G. Wolinsky, MD.

Approved by the American Society of Nuclear Cardiology Board of Directors, September 7, 2006.

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