It is imperative in all areas of diagnostic imaging that interpreting physicians are well trained to recognize not only the considerable variation that exists in the “normal” study, but also the many deviations that may occur from a variety of technical factors. This may be more pertinent for radionuclide imaging than other areas of diagnostic imaging. The radiopharmaceuticals that we administer go through a fairly elaborate process related to their preparation. Even slight deviations can lead to radiochemical or radiopharmaceutical impurities. Labeling problems and variants associated with administration technique can significantly change the distribution of activity on a radionuclide image. Patient preparation, such as fasting, blood glucose levels, etc, play an important role as well.
In their lead article, Dr. Shankar Vallabhajosula and his associates at Cornell present a wonderful, thorough review of the many things that may go wrong in the process of preparing a radiopharmaceutical. “Shankar,” as he is known to his many friends and colleagues, has generously shared with us his enormous fund of knowledge in this most important overview. It should certainly provide us with a standard reference source for many years to come.
The recognition of altered biodistribution should allow one to avoid pitfalls and recognize artifacts existent on a variety of clinical studies. The 18F-fluorodeoxyglucose posiptron emission tomography (FDG-PET) scan has considerable variability. One of the most commonly encountered variants relates to enhanced localization in brown fat. Dr. Christian Cohade thoroughly reviews this subject and presents his views on possible mechanisms for this frequently encountered finding. He also deals with the very important issue of glucose and insulin levels and their impact on FDG distribution. In a separate article, Liu and coworkers describe many of the pitfalls, artifacts and incidental findings associated with FDG-PET imaging and how they can be recognized.
The conventional bone scan with 99mTc-methylene diphosphonate is associated with some of the most striking cases of altered biodistribution. When interesting and unusual cases are presented at conferences, they are very often bone scans. Uptake secondary to nonosseous areas of dystrophic calcification or ossification account for most of these findings. Changes in pharmaceutical preparation, such as aluminum break through while eluting a 99Mo/99mTc generator, may cause liver uptake on a bone scan. This and the many other relevant altered biodistribution bone scan patterns are review by Zuckier and Freeman.
A radiologist -in-training is taught to look at “all four corners” of a study so as not to miss any unexpected or unrelated findings. Looking at “all four corners” of our most frequently performed myocardial perfusion studies can be rewarding when it results in discovering an unsuspected finding related to unusual localization of thallium or sestamibi. Drs. Chamarthy and Travin show us some interesting examples of this.
Finally, imaging for infection with both gallium-67 citrate and 111In-labeled white blood cells may be associated with some unusual and unexpected findings related to altered biodistribution. No one is more experienced in this area than Dr. Chris Palestro. Drs. Love and Palestro nicely review this area for us in detail.
Overall, this issue should provide a most useful reference source for those interpreting radionuclide images on a day-to-day basis. As is necessary in this type of review, the large number of illustrations give this issue an “atlas-like” flavor. We hope that you enjoy it. However, despite the many images, the underlying concept that radionuclide imaging represents function and not morphology holds true and governs our interpretations.
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