Abstract
BackgroundThe current lack of a standardized protocol for positioning of the gamma camera relative to the horse limb in a lateral stifle scintigram, and thus the reliance on subjective positioning, may be a cause of diagnostic error and inter-operator variability due to variations of the view angle. The aims of this study were to develop a reliable method to obtain a lateral scintigram of the equine stifle based on fixed anatomical landmarks and measure the resulting foot to gamma camera angle on sequential measurements of the same horse and of different horsesMethodsTechnetium filled capsules were glued on the skin on sites adjacent to the origin of the medial and lateral femorotibial collateral ligaments in 22 horses using ultrasound guidance. A lateral view of the stifle was defined as the image where the two radioactive point sources were aligned vertically (point sources guided method). Five sequential lateral acquisitions (one to five) of the stifle with the point sources vertically aligned were acquired in each horse, and the angle between the mid-sagittal foot-axis and the vertical axis of the gamma camera (FC angle) was measured for each of these acquisitionsResultsFor acquisition group one to five, the mean of the means FC angle was 91.6 ± 2° (2SD) and the coefficient of variation (COV) was 1.1%. In the 22 horses the 95% CI for the mean FC angles was 91.6° ± 12.1° (2SD) and the COV was 6.6%.ConclusionsThe use of point sources to guide gamma camera position results in less variation in the lateral scintigram than if the distal limb is used as guidance due to a difference in FC angle between horses. The point source guided positioning method is considered suitable as a reference standard method to obtain lateral scintigrams of the equine stifle, and it will be of value in clinical scintigraphy and research. The use of alignment of specifically located point sources may also be applied in other regions to standardize scintigraphic views.
Highlights
The current lack of a standardized protocol for positioning of the gamma camera relative to the horse limb in a lateral stifle scintigram, and the reliance on subjective positioning, may be a cause of diagnostic error and inter-operator variability due to variations of the view angle
The aims of this study were to develop a reliable method to obtain a lateral scintigram of the equine stifle based on fixed anatomical landmarks and measure the resulting foot to gamma camera angle (FC angle) on sequential measurements of the same horse and of different horses
The low coefficient of variation (COV) (1.1%) for repeated FC angle acquisitions using the point sources guided method supports our hypothesis that a method based on landmarks positioned on anatomical structures of the stifle should result in a consistent FC angle for lateral scintigrams of the same horse
Summary
The current lack of a standardized protocol for positioning of the gamma camera relative to the horse limb in a lateral stifle scintigram, and the reliance on subjective positioning, may be a cause of diagnostic error and inter-operator variability due to variations of the view angle. The aims of this study were to develop a reliable method to obtain a lateral scintigram of the equine stifle based on fixed anatomical landmarks and measure the resulting foot to gamma camera angle on sequential measurements of the same horse and of different horses. The distribution of the radiopharmaceutical uptake (RU) in the tissues is represented by the distribution of counts per pixel in the scintigram. The subjective evaluation relies on the knowledge of the normal variations of the RU pattern expected in a specific anatomical region. Objective evaluation of scintigrams is based on the number of counts per pixel in a defined region of interest (ROI). Since a ROI only examines a small part of the image precise anatomical placement of the ROI is essential to avoid misinterpretations and accuracy can be achieved only if reliable scintigraphic views are obtained
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