Equine skeletal scintigraphy: Comparing normal bone‐to‐soft tissue ratio 2 and 4 hours after injection with either hydroxymethylene diphosphonate or methylene diphosphonate

Abstract

Background: In equine skeletal scintigraphy, there is no information about the possible influence of different phosphonate compounds on image quality. Methods: This prospective randomised study determined bone uptake changes and image quality for hydroxymethylene diphosphonate (HDP) and methylene diphosphonate (MDP) in equine patients at different time points. Scintigraphic images of the radius and the tibia of 20 horses were acquired at 2 and 4 hours after injection of either technetium-labelled HDP or MDP. Three regions of interest were identified-in the bone diaphysis, adjacent soft tissue and background area-to determine the normal bone-to-soft tissue ratio (BSR). Qualitative analysis was performed using a modified scoring system. Results: In terms of BSR and count rates, HDP showed a slightly better incorporation into bone compared to MDP, but significant differences were only detected for count rates at 4 hours after injection (p = 0.048). The radiopharmaceutical used did not influence qualitative image scoring, which was correlated with the BSR (ρ = 0.49; p ≤ 0.001). Conclusion:The choice of HDP or MDP for equine skeletal scintigraphy does not seem to substantially affect BSR and qualitative image scoring. Further studies with a larger sample size, including the evaluation of lesion detection ability for both bone-seeking agents, are needed.

Equine skeletal scintigraphy: Comparing lesion detection ability of methylene diphosphonate and hydroxymethylene diphosphonate in the caudal cervical and proximal metacarpal/metatarsal regions

“…3,15 The overall lower bony uptake of MDP may have ameliorated subjective assessment within the PMR group, also leading to the higher lesionto-normal bone ratios calculated within the same group. 7 In the present study, the results of subjective image evaluation are undermined by the very low agreement between the three clinicians, regardless of their similar degree of experience in evaluating equine bone scintigrams. Other examinations already reported a poor interobserver agreement for the evaluation of equine bone scans.…”

“…However, previous authors have already described the qualitative difference between the two radiopharmaceuticals, as measured by the overall count rate. 7 To increase the probability that the areas of IRU analysed in this study represented 'true' lesions, a thorough clinical examination was performed and further imaging modalities were combined to reach the final diagnosis. The identification of IRU by three orthopaedic surgeons in a clinical setting may have introduced selection bias.…”

“…Even if free-hand ROI drawing has been reported as a suitable method for semiquantitative scintigraphic analysis of equine cheek teeth, 40 we favoured a standardised ROI size, as reported in other musculoskeletal studies. 7,8 Due to slight differences in lesion size and form within the PMR groups, the standardised ROIs may have included a small amount of healthy bone and/or soft tissues when placed over comparably small lesions. Despite this fact, no significant differences regarding the distribution of count numbers per ROI lesion were observed within the two PMR groups.…”

“…and J.B.), using the same image viewing program (easyIMAGE software, Veterinärmedizinisches Dienstleistungszentrum [VetZ]) on high-resolution computer screens (Dell TFT U2412M, Dell). Each image was evaluated by each blinded observer within a period of 3 days, according to the following scoring system 7 : The results of the qualitative scoring were used to assess interobserver agreement.…”

“…[3][4][5][6] Recently, this topic was also addressed in equine bone scintigraphy. 7,8 In these studies, images were compared both quantitatively (region of interest [ROI] analysis, bone-to-soft tissue ratio calculation) and than for HMDP, 3,16 possibly due to the lower bony uptake of MDP. These results support the theory that higher absolute skeletal uptake results in ineffective lesion detection ability, especially for lower grade or early-stage lesions.…”