"Diagnostic Imaging" TUMOR TIDBITS, A BIWEEKLY EMAIL NEWSLETTER FROM GULF COAST VETERINARY ONCOLOGY Number 88; February 14, 2003. ======================================================================= THIS WEEK'S TUMOR TIDBIT: Diagnostic Imaging ======================================================================= ANNOUNCEMENTS March 15th is our Second Annual Patient Celebration in Houston - all are welcome. March 4th we begin offering 3 day per week service in San Antonio. April 1st we begin a clinical trial for anemia with free cancer services in both clinic locations. Visit our web site for other exciting information. ======================================================================= Creating diagnostic images with x-rays, ultrasound, computed tomography, magnetic resonance, and scintigraphy has become increasingly sophisticated and important in detecting, diagnosing, and monitoring treatment responses in patients with tumors. Image resolution, contrast, and distortion determine the value of the different imaging techniques in clinical assessment, staging, and re-evaluation. Diagnostic imaging assists in evaluation by helping to assess the margins of a neoplasm with respect to size, metastasis, and degree of invasiveness. The sensitivity and specificity of each imaging technique vary, and as a result, the ability to clearly distinguish tissue margins differs. Survey radiographs provide excellent spatial resolution compared with other modalities of imaging; however, contrast discrimination between normal and neoplastic soft tissue is poor. Invasiveness and tissue architecture cannot be assessed, and soft-tissue structures in contact with one another cannot be distinguished as separate entities if they have the same physical density. Definitive characterization of parenchymal disease requires histopathological review. Medical gray scale ultrasonography can be used to create images of a tumor and provide more information about soft-tissue architecture and size than is available from survey radiographs alone. Ultrasonography does not define spatial resolution as well as radiography because images are displayed as anatomical reconstructions of a tissue slice made by the ultrasound beam. Sharp definitions of the far margins of a mass are limited by the heterogeneity of echoic and anechoic signals from many composite structures. Ultrasonography cannot image through bone or air, so it is not possible to image the brain, spinal cord, lung, or an air-filled gastrointestinal tract directly. Diffuse and focal parenchymal disease can be determined but not definitively characterized. Definitive characterization of parenchymal disease requires biopsy. Abdominal fluid does not interfere with the creation of an ultrasonographic image as it does with standard radiographs. Cystic structures can usually be identified with ultrasonography, and machines with Doppler capabilities can determine and assess blood flow. Image quality and tissue orientation rely heavily on the skill of the ultrasonographer. Computed tomography allows excellent contrast discrimination among different tissue types. Two-dimensional images can be constructed in the dorsal, sagittal, and transverse planes for determining accurate tumor measurements. The physical density of a tumor may be compared with normal tissues to provide information on size or degree of invasiveness. As with ultrasonography, spatial resolution is poor with computed tomography because only one slice of tissue at a time is available for examination, but the unique cross-sectional imaging ability of computed tomography makes it possible to detect soft tissues independent of overlying bony structures. Magnetic resonance imaging, for the same reasons as for ultrasonography and computed tomography, is characterized by poor spatial resolution, but it has contrast capabilities superior to computed tomography. The major advantage of magnetic resonance imaging over computed tomography is in diagnostic evaluation of the central nervous system. Scintigraphic images are made by using a gamma camera to detect the amount of a radiopharmaceutical agent that distributes to the tissue under study. Facilities for scintigraphy are available at numerous veterinary schools and at several private veterinary medical facilities. The use of scintigraphy in evaluating dogs and cats with thyroid disease is well documented. Nuclear medicine has many other diagnostic uses, including biliary scans, bone scans, assessment of ventricular performance, liver and spleen scans, lung perfusion scans, and others. Bone scintigraphy is more sensitive than survey radiography for detecting primary and secondary bone tumors. Subtle abnormalities in bone attributed to early metastasis may not be easily recognized with survey radiography but may be identified with scintigraphy and confirmed with specific radiographs and bone biopsy. Skeletal metastasis can be detected earlier with scintigraphy than with radiography because scintigraphic images depend more on the bone remodeling that develops before the structural changes detected with radiography. In a study of 25 dogs with appendicular or axial osteosarcoma, 14 had scintigraphically enhanced sites beyond the primary tumor site, with 7 of the 14 sites subsequently being histopathologically confirmed as osteosarcoma. Inflammation, trauma, and neoplasia can account for scintigraphic enhancement of bone; therefore, scintigraphy does not differentiate benign from malignant bone disease. Scintigraphically suspicious sites should be radiographed and biopsy performed to establish a definitive diagnosis Clinicians should consider several general principles in deciding which of these tests should be done and which should come first. Cancers of each organ tend to spread to certain parts of the body, usually near the organ where they started. For this reason, the choice of tests may depend on where a metastasis is found. Choice of tests would also depend on which cancers are likely to occur in a pet depending on the pet's age and gender. In choosing tests, try to start with ones that are not painful, do not cause serious complications, and are not too expensive. If these do not find the source of a cancer, then other tests are considered. Let us know at Gulf Coast Veterinary Oncology (& Diagnostic Imaging) if we can assist in any way possible. Our clinic offers full Diagnostic Imaging Services as described above. ======================================================================= As always, we hope this info helps and don't hesitate to call or email us Gulf Coast Veterinary Oncology! Kevin A. Hahn, DVM, PhD, Diplomate ACVIM (Oncology), drhahn@gcvs.com Janet K. Carreras, VMD, Diplomate ACVIM (Oncology), drcarreras@gcvs.com Glen K. King, DVM, MS, Diplomate ACVR (Radiology & Radiation Therapy), drking@gcvs.com Gulf Coast Veterinary Diagnostic Imaging & Oncology 1111 West Loop South, Suite 150, Houston, TX 77027 P: 713.693.1166 F: 713.693.1167 W: www.gcvs.com