F-NaF PET imaging of the Thoroughbred fetlock is feasible and compares favourably with other imaging modalities in detecting stress remodelling in Thoroughbred racehorses. PET appears to be a beneficial imaging modality when used for early detection of stress remodelling in an effort to prevent catastrophic musculoskeletal injuries in this population of horses.
Maximal standardized uptake values (SUVmax) are commonly used for the interpretation of PET studies. Limited information regarding the SUVmax of 18F‐NaF PET in horses is currently available in the literature. The goals of this retrospective secondary analysis study were to provide reference values for 18F‐NaF SUVmax in the equine distal extremity and assess the effect of attenuation correction. Nonattenuation corrected (NAC) and CT‐based attenuation corrected (CTAC) SUVmax were obtained from 19 feet and 19 fetlocks. Twenty regions of interest (ROIs) were defined for the foot and 22 for the fetlock. Areas presenting abnormal uptake were excluded. The overall NAC and CTAC SUVmax were 3.6 +/‐ 1.5 (mean +/‐ sd) and 5.0 +/‐ 1.8 for the feet and 2.9 +/‐ 1.1 and 3.8 +/‐ 1.4 for the fetlocks, respectively. The 3 ROIs showing the highest attenuation correction were the navicular center (83.4%), navicular flexor surface (74.9%) and distal phalanx flexor surface (81.3%), whereas attenuation correction was only 5.2% at the dorsal aspect of the proximal phalanx. Significant SUVmax differences were observed between the different ROIs (P < 0.0001), with the toe (CTAC SUVmax 7.7 +/‐ 3.7), dorsal (7.5 +/‐ 1.9) and central (6.1 +/‐ 2.2) ROIs of the distal phalanx being significantly higher than those of the other areas. This study demonstrates that attenuation correction affects SUVmax in the equine distal extremity and should be performed if CT data are available. However, as the maximal attenuation correction results in less than doubling the signal intensity, nonattenuation corrected images likely remain relevant for subjective clinical interpretation.
F-NaF PET imaging of the equine distal limb provides useful additional information when compared with CT, MRI and scintigraphy and has the potential for both research and clinical applications in the horse. The Summary is available in Chinese - see Supporting information.
Positron emission mammography (PEM) provides images of biochemical activity in the breast with spatial resolution matching individual ducts (1.5 mm full-width at half-maximum). This spatial resolution, supported by count efficiency that results in high signal-to-noise ratio, allows confident visualization of intraductal as well as invasive breast cancers. Clinical trials with a full-breast PEM device have shown high clinical accuracy in characterizing lesions identified as suspicious on the basis of conventional imaging or physical examination (sensitivity 93%, specificity 83%, area under the ROC curve of 0.93), with high sensitivity preserved (91%) for intraductal cancers. Increased sensitivity did not come at a cost of reduced specificity. Considering that intraductal cancer represents more than 30% of reported cancers, and is the form of cancer with the highest probability of achieving surgical cure, it is likely that the use of PEM will complement anatomic imaging modalities in the areas of surgical planning, high-risk monitoring, and minimally invasive therapy. The quantitative nature of PET promises to assist researchers interested studying the response of putative cancer precursors (e.g., atypical ductal hyperplasia) to candidate prevention agents.
Positron emission tomography (PET) is a highly sensitive, noninvasive imaging technique for quantifying biological functions of tissues. However, at the time of this study, PET imaging applications had not been reported in the horse. The aim of this exploratory study was to determine whether a portable high-resolution PET scanner could be used to image the equine distal limb. Images of the front feet and fetlocks of three research horses, with known lesions localized to the distal front limbs, were acquired under general anesthesia after administration of F-fluorodeoxyglucose ( F-FDG), with doses ranging from 1.5 to 2.9 MBq/kg. The radiation exposure measured during imaging was slightly higher than Technetium scintigraphy. However, the use of general anesthesia allowed the proximity and the contact time with the patient to be minimized for the staff involved. F-FDG uptake was evident throughout the soft tissues, with the highest uptake in the coronary band and the lowest uptake in the tendons. Anatomic structures could be discriminated due to the high contrast between soft tissue and bone. Detected lesions included lysis of the flexor cortex of the navicular bone, lesions of flexor tendons and suspensory ligament, and abnormal uptake through the lamina of a laminitic subject. Findings indicated that tomographic molecular imaging is feasible in the equine distal limb and could be useful as a future diagnostic technique for clinical and research studies, especially those involving tendinopathy/desmopathy and laminitis.
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