Nuclear medicine computers now commonly offer resolution recovery and other software techniques which have been developed to improve image quality for images with low counts. These techniques potentially mean that these images can give equivalent clinical information to a full-count image. Reducing the number of counts in nuclear medicine images has the benefits of either allowing reduced activity to be administered or reducing acquisition times. However, because acquisition and processing parameters vary, each user should ideally evaluate the use of images with reduced counts within their own department, and this is best done by simulating reduced-count images from the original data. Reducing the counts in an image by division and rounding off to the nearest integer value, even if additional Poisson noise is added, is inadequate because it gives incorrect counting statistics. This technical note describes how, by applying Poisson resampling to the original raw data, simulated reduced-count images can be obtained while maintaining appropriate counting statistics. The authors have developed manufacturer independent software that can retrospectively generate simulated data with reduced counts from any acquired nuclear medicine image.
Half of the participating centres could potentially make use of resolution recovery to reduce the administered activity for myocardial perfusion scans without changing their routine acquisition protocols. The other half could consider adjusting the reconstruction parameters used with their resolution recovery software if they wish to use reduced activity successfully.
The widespread adoption of the guidelines has harmonized national GFR calculation compared with the previous audit. Further standardization could further reduce variability. This audit has highlighted the need to address the national standardization of QC methods. Radionuclide techniques are confirmed as the preferred method for GFR measurement when an unequivocal result is required.
The audit concluded that the practical implementation of filtering, such as the size of the kernel, has a profound effect on the results, producing large differences between systems. Nevertheless, this work shows how users can quantify the frequency response of their own systems so that it will be possible to compare two systems in order to find filter parameters on each that produce equivalent results. These findings will also make it easier for users to replicate filters similar to other published results, even if they are using a different computer system.
A 28-year-old woman presented with weight loss and tiredness. Investigations revealed hyperthyroidism. She was commenced on treatment and later became pregnant. Her thyroid levels remained raised, and she later underwent an elective cesarean delivery and ovarian cystectomy. Only a partial cystectomy was achieved, and histopathology examination revealed struma ovarii. An isotope uptake scan ((123)I) including her pelvis revealed low uptake in the thyroid gland and an area of high uptake in her pelvis. The cyst was subsequently removed, and within days, her thyroid hormone levels dropped. This case illustrates the importance of considering uncommon causes of hyperthyroidism.
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