AQARA Requirements for Radionuclide-Based Images

AQARA Requirements for Radionuclide-Based Images

To best convey the quantitative information in nuclear images and to standardize their display, all PET, SPECT and planar nuclear images submitted for publication must provide “as much quantitative information as reasonably achievable” (AQARA) as described in the five (5) key requirements listed below. Guidance for the AQARA requirements was originally published in: Weber WA, Bengel FM, Blasberg RG. The AQARA principle – proposing standard requirements for radionuclide-based images in medical journals. J Nucl Med. 2020;61(1):1-2.

1. If feasible, the intensity-scale bar should be in absolute units, for example, Bq/mL or SUVs. This is the best way to ensure standardized display of images, independent of the specific distribution of radioactivity in an individual scan. Absolute scaling is almost always feasible for PET images and is becoming more common for SPECT images as well. If parametric images showing biologically relevant parameters (such as rate constants, metabolic rates, volumes of distribution, or binding potentials) are available, they should generally be preferred to images of physical parameters such as activity concentrations. The unit used for the scale bar should always be displayed within the image, such as at one side of the scale bar.
2. When no absolute scaling of images is feasible or reasonable (e.g., in myocardial rest/stress perfusion SPECT images), a relative-scale bar should be used. Images may then be scaled to the maximum activity in the displayed image or the investigated organ. The unit of the scale bar would then be percentage of maximum, and the top and bottom values should be identified accordingly. When several images of a tracer are shown within a single published article, they should preferably be displayed with the same upper and lower window settings to facilitate comparisons.
3. Setting pixels with a value below a certain threshold to a background color (background subtraction) should generally be avoided. If necessary or useful for a better display of a specific image feature, the background subtraction should be clearly indicated in the scale bar. The bottom of the scale bar should still be labeled as ‘‘0,’’ and the fraction of the scale bar below the background value should be displayed in the background color to indicate the degree of background subtraction.
4. Overlaying of PET and SPECT images on top of anatomically coregistered CT and MR images (image fusion) is helpful to display the exact location of findings on PET and SPECT images. However, during the coregistration process, some information from the PET and SPECT images can be lost. For example, low-grade tracer uptake in areas that are dark on CT and MR images may become difficult or impossible to evaluate. Therefore, figures should show not only fused images but also the individual PET and SPECT images. Preferably, these images should be displayed in a black-on-white intensity scale.
5. Cropping of images should be limited, except for well established imaging procedures such as myocardial perfusion. If cropping is necessary to show small details, an uncropped image illustrating the tracer distribution in the entire field of view should additionally be shown—as a supplementary figure, for example. This proposed requirement is especially important for reports on new radiopharmaceuticals.

%IA/cm³ = percentage of injected activity per cubic centimeter of tissue.