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Background: Microbrachytherapy enables high local tumor doses sparing surrounding tissues by intratumoral injection of radioactive holmium-166 microspheres (166Ho-MS). Magnetic resonance imaging (MRI) cannot properly detect high local Ho-MS concentrations and single-photon emission computed tomography has insufficient resolution. Computed tomography (CT) is quicker and cheaper with high resolution and previously enabled Ho quantification. We aimed to optimize Ho quantification on CT and to implement corresponding dosimetry. Methods: Two scanners were calibrated for Ho detection using phantoms and multiple settings. Quantification was evaluated in five phantoms and seven canine patients using subtraction and thresholding including influences of the target tissue, injected amounts, acquisition parameters, and quantification volumes. Radiation-absorbed dose estimation was implemented using a three-dimensional 166Ho specific dose point kernel generated with Monte Carlo simulations. Results: CT calibration showed a near-perfect linear relation between radiodensity (HU) and Ho concentrations for all conditions, with differences between scanners. Ho detection during calibration was higher using lower tube voltages, soft-tissue kernels, and without a scanner detection limit. The most accurate Ho recovery in phantoms was 102 ± 11% using a threshold of mean tissue HU + (2 × standard deviation) and in patients 98 ± 31% using a 100 HU threshold. Thresholding allowed better recovery with less variation and dependency on the volume of interest compared to the subtraction of a single HU reference value. Corresponding doses and histograms were successfully generated. Conclusion: CT quantification and dosimetry of 166Ho should be considered for further clinical application with on-site validation using radioactive measurements and intra-operative Ho-MS and dose visualizations. Relevance statement: Image-guided holmium-166 microbrachytherapy currently lacks reliable quantification and dosimetry on CT to ensure treatment safety and efficacy, while it is the only imaging modality capable of quantifying high in vivo holmium concentrations. Key Points: Local injection of 166Ho-MS enables high local tumor doses while sparing surrounding tissue. CT enables imaging-based quantification and radiation-absorbed dose estimation of concentrated Ho in vivo, essential for treatment safety and efficacy. Two different CT scanners and multiple acquisition and reconstruction parameters showed near-perfect linearity between radiodensity and Ho concentration. The most accurate Ho recoveries on CT were 102 ± 11% in five phantoms and 98 ± 31% in seven canine patients using thresholding methods. Dose estimations and volume histograms were successfully implemented for clinical application using a dose point kernel based on Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Residual thymic tissue is a common incidental finding in thoracic CT of human adults. To determine whether presumed residual thymic tissue is also a common incidental finding in adult dogs, a two part‐study was performed. The first part was a prospective, descriptive design where CT examination was performed in six canine cadavers within 24 h after death and presumed residual thymic tissue was examined pathologically. The second part of the study was a retrospective, analytical design where medical records of our institution were searched for thoracic CT scans of adult dogs performed in the year 2020. Age, sex, breed, presence of presumed thymic tissue, location, shape, attenuation, homogeneity, and width of the tissue were recorded and comparisons were performed using these data. In 4 of 6 of the prospective cases, thymic tissue was present on histology and in 2 of 6 dogs the presence of thymic tissue could not be confirmed. For the retrospective study, in 161/169 (95.3%) cases with presumed residual thymic tissue were detected. Shape and size were highly variable with either homogeneous (46.6%), heterogeneous (42.9%), or mixed (10.6%) attenuation. Dogs with presumed residual thymic tissue were significantly younger (median: 9.1 years; range: 1.2–14.3 vs. median: 10.5 years; range: 9.4–12.3) as were dogs with homogeneous attenuation of the tissue (median: 8.1 years; range: 1.2–14.3 vs. median: 9.5 years; range: 4.0–14.3). In conclusion, results indicated that presumed residual thymic tissue is a common CT finding in adult dogs and can be considered incidental. [ABSTRACT FROM AUTHOR]

Part 2: The radiologist's perspective This clinical forum will review pancreatic disease in dogs, primarily focusing on those patients that go on to develop obstruction of the biliary tree. A series of commonly asked questions relating to pancreatitis and concurrent biliary tract obstruction will be asked of a panel of specialists with varying views expressed! In the August 2013 issue of Companion Animal, a further article on this topic will be published giving both a surgeon's perspective on canine pancreatitis and biliary duct obstruction. [ABSTRACT FROM AUTHOR]

Objectives--To determine the effect of sedation and anesthesia on thyroid and salivary gland uptake of technetium Tc 99m pertechnetate (99mTcO4) in euthyroid cats. Animals--6 euthyroid cats. Procedures--Thyroid scintigraphy was performed by use of a high-resolution low-energy parallel-hole collimator after IV injection of 117 to 133 MBq (3.16 to 3.59 mCi) of 99mTcO4-. The procedure was performed 4 times on each cat during different sedative and anesthetic protocols in a rotating schedule as follows: propofol, ketamine-midazolam-atropine, ketamine-midazolam, and medetomidine. Regions of interest were drawn around thyroid and salivary glands and counts corrected for background and decay. Percentage of 99mTcO4- uptake in salivary and thyroid glands and thyroid-to-salivary gland 99mTcO4- uptake ratio were calculated at 20 and 40 minutes. Relative effects of anesthesia and sedation on salivary and thyroid gland 99mTcO4- uptake were compared. Results--Significant differences among sedative-anesthetic protocols were found for thyroid gland 99mTcO4- uptake, salivary gland 99mTcO4- uptake, and thyroid-to-salivary gland 99mTcO4- uptake ratio. Thyroid gland 99mTcO4- uptake for the ketamine-midazolam protocol at 20 and 40 minutes after 99mTcO4- administration was significantly higher than for the propofol protocol. A significant difference in salivary gland 99mTcO4- uptake was found between ketamine-midazolam and ketamine-midazolam-atropine protocols at 40 minutes. The thyroid-to-salivary gland 99mTcO4- uptake ratio for the ketamine-midazolam protocol was significantly higher at 40 minutes than for propofol or ketamine-midazolam-atropine protocols. Conclusions and Clinical Relevance--Sedation and anesthesia have a significant effect on thyroid and salivary gland 99mTcO4- uptake in euthyroid cats that may interfere with thyroid scintigraphic image interpretation. [ABSTRACT FROM AUTHOR]