A scanogram is a type of medical imaging that uses X-ray technology to capture a broad view of a patient’s internal structures. Serving as a preliminary or measurement tool, this quick, low-dose examination gathers initial information before a more intensive diagnostic test or to provide highly accurate anatomical measurements. It acts as a “scout” image, helping medical professionals plan and guide the precise focus of subsequent, detailed imaging procedures.
Defining the Scanogram
A scanogram is a digital radiographic image often called a scout film, topogram, or surveylogram, depending on the equipment manufacturer. It is an initial, low-resolution picture taken to map out the body region of interest for a following imaging study, most commonly a Computed Tomography (CT) scan. This preliminary image allows the technologist to accurately set the parameters for the detailed CT, such as defining the exact start and end points for the cross-sectional slices. It is typically acquired quickly, with the X-ray tube moving over the area to be scanned while the patient remains still.
Primary Clinical Applications
The most common application of a scanogram is the accurate measurement of bone length, particularly in the lower limbs, where it is frequently referred to as a “long leg scanogram” or orthoroentgenogram. This technique is used to assess a condition known as limb length discrepancy (LLD), where one leg is shorter than the other. The scanogram captures a continuous image of the legs from the hips to the ankles, allowing clinicians to precisely measure the length of the femur and tibia bones.
Another primary use is localization, which involves precisely identifying the location of specific anatomical landmarks, foreign objects, or suspected pathology. For instance, a scanogram is used in pre-surgical planning for orthopedic procedures to determine alignment issues like bowlegs or knock knees. By providing an undistorted, full-length view, it helps surgeons plan corrective procedures, track post-surgical healing, or define the exact area for a more targeted biopsy or intervention.
The Patient Experience: What Happens During the Procedure
Preparation for a scanogram is minimal, usually requiring the patient to remove any metallic objects, such as jewelry or clothing with zippers, that could interfere with the X-ray image. The patient is asked to lie flat on the imaging table, though they may be asked to stand for weight-bearing measurements, especially for long leg studies. Precise positioning is crucial, and the technologist may use positioning aids to ensure the limbs or spine are straight and correctly aligned.
Once positioned, the patient is instructed to remain completely still while the imaging machine acquires the image. For a long leg scanogram, the X-ray tube moves slowly down the length of the body, capturing a continuous series of images that are stitched together digitally to create one long, seamless view. The entire process is very quick, often lasting less than five minutes, and the patient does not typically feel any sensation during the image acquisition.
Safety and Radiation Exposure
A common concern for patients undergoing any X-ray procedure is exposure to ionizing radiation. The scanogram is designed to be a low-dose procedure, especially when used as a preliminary scout image for a CT scan. The radiation dose from a scanogram is significantly lower than that of a full diagnostic X-ray or a comprehensive CT scan, which uses multiple cross-sectional beams.
The goal of using a scanogram before a CT is to minimize the overall radiation dose by ensuring the subsequent, more detailed scan is perfectly targeted and does not need to be repeated. By mapping the area precisely, the technologist avoids scanning unnecessary regions of the body. While any radiation exposure carries a small risk, the dose from a scanogram is carefully controlled and considered safe, providing valuable diagnostic information that outweighs the minimal exposure.