Читать книгу Fractures in the Horse - Группа авторов - Страница 115

Acquisition of images has become increasingly uniform and refined and, in most facilities, follows a set protocol. Images should overlap to ensure that the entirety of the requested areas is evaluated. The field of view of the gamma camera detector will have a bearing on the number of images required to achieve this. In man, at least two orthogonal views of stress fractures are obtained to evaluate the degree of cortical penetration [48].

Although protocols have been documented [94, 95], each patient should have the study tailored and modified according to the appearance of the images as they are being acquired. Real‐time assessment is therefore optimal. In addition to standard acquisition protocols, the following views can provide additional information;

 Dorsal and oblique images of the spine help to differentiate IRU in laminar arches and spinous processes.

 Lateral (costal fovea to costochondral junction) and dorsal images of the ribs will confirm IRU within ribs rather than superimposed structures. Cranial images of the thoracic inlet (Figure 5.9c) and a modified lateral image with the forelimb closest to the detector pulled backwards [96] permit assessment of cranial rib fractures.

 Oblique images of the cranial [97] and caudal pelvis reduce superimposition together with soft tissue and distance attenuation and can better image ilial wing, ilial shaft, ischial and pelvic floor fractures. They also help differentiate proximal ilial wing, tuber sacrale and sacral fractures as these areas are superimposed in dorsal images. It can also differentiate lesions when there is a question over possible superimposed urine pooling: if the IRU is within the skeleton it will maintain a constant relationship with the bone irrespective of gamma camera position (Figure 5.8).Figure 5.8 Adult warmblood showjumper that went acutely lame in its left hindlimb while jumping. (a) Initial nuclear scintigraphy study 48 hours post lameness. Note activity from excreted 99Tc‐MDP in the urinary bladder superimposed over the cranial left ilial shaft (dashed blue circle) and how the presence of both the urinary bladder and motion artefact degrades the dorsal pelvis image quality. (b) Second study nine weeks post lameness. Diffuse area of marked IRU involving the caudal left ilial wing and cranial ilial shaft (arrows) consistent with a fracture.

 In addition to the standard view of the tuber ischii (detector positioned at 45° to vertical with the tail lifted to one side to avoid overlay and effacement of the axial ischium and symphysis), positioning the detector at 90° (again with the tail lifted to the side) can give further information regarding fractures of the ischium and tuber ischium.

 Proximal tibial stress fractures can occasionally be present caudomedially and have the potential to be overlooked on the lateral view if IRU is mild. Additional caudal views of the stifle are recommended.

 Mid‐diaphyseal tibial fractures can be missed if there is inadequate overlap between lateral hock and lateral stifle views, especially if the detector field of view is small: a lateral image of the entire tibia is useful.

 A combination of dorsal and lateral views of the scapula can differentiate stress fractures of the scapula and vertebral lesions [39].

 Cranial views of the shoulder and proximal humerus aid identification of deltoid tuberosity fractures.

 A cranial view of the elbow and distal humerus can highlight subtle IRU in the distal medial humerus (stress fracture) or in the medial humeral subchondral bone (compression fracture): on lateral projections alone both can be obscured by attenuation.

 A flexed dorsal view of the carpus separates the carpal bones and helps in identification and localization of lesions.

 Flexed lateral views of the fetlocks can help separate the metacarpal/metatarsal condyles from the proximal sesamoid bones and change the orientation of the condyle with the proximal phalanx.

 Flexed dorsal views of the fetlocks can differentiate parasagittal IRU from condylar IRU [98].Figure 5.9 Scintigrams of the proximal forelimb of a two‐year‐old Thoroughbred racehorse with acute onset right forelimb lameness. (a) Lateral scintigram centred on the scapulae. Normal symmetrical metabolic activity in the proximal humeral physes is evident, which produces count capture. An area of abnormal IRU is indicated (blue arrow). (b) Postprocessing masking of the physes highlights the abnormal IRU more clearly. (c) Following identification of the abnormal IRU, contemporaneous additional cranial projections were acquired. IRU in the proximal aspect of the first right rib is confirmed and highlighted (blue arrows).

 Solar views of the foot can provide further information for distal phalangeal and navicular bone fractures.

In skeletally immature individuals, there is normal intense localization of ^99mTc‐MDP in the physes. As this produces count capture, it is important to mask these areas during post‐processing to ensure that areas of abnormal IRU are not obscured (Figure 5.9).