This article will focus on the basics of creating high-quality thoracic radiographs of the dog and cat as well as the role that veterinary nurses/technicians can take in obtaining these images. Show
Danielle Mauragis, CVT, is a radiology technician at University of Florida College of Veterinary Medicine, where she teaches diagnostic imaging. She coauthored the Handbook of Radiographic Positioning for Veterinary Technicians and received the Florida Veterinary Medical Association’s 2011 Certified Veterinary Technician of the Year award. Read Articles Written by Danielle Mauragis Clifford R. BerryDVM, DACVR Dr. Berry is an adjunct professor of diagnostic imaging at the University of Florida and a clinical assistant professor of diagnostic imaging at North Carolina State University College of Veterinary Medicine. He received his DVM from University of Florida and completed a radiology residency at University of California–Davis. He has a specific interest in diagnostic imaging of the thorax. Updated October 2022 Read Articles Written by Clifford R. Berry This article is the first in a series of articles that will discuss various radiographic positions and techniques. The veterinary technician plays a critical role in the development and maintenance of a radiographic program at a veterinary practice. Thus, it is the responsibility of the technician to be familiar with the basics of:
The purpose of this article is to review the 3 basic components of creating high-quality thoracic radiographs of the dog and cat, including positioning, technique, and quality control of the final images. With advances in imaging technology (computed and digital radiography), errors in technique are less common; however, if anatomy is not appropriately collimated and positioning is inadequate, all imaging studies can be rendered nondiagnostic. A routine thoracic radiographic study includes 3 projections: right and left lateral images and a ventrodorsal (VD) or dorsoventral (DV) image. Radiography Lingo Anode: An electrically positive terminal of a radiographic tube that emits x-rays from the point of impact of the electron stream from the cathode. Cathode: The negative side of the radiographic tube where electrons are emitted; it consists of the focusing cup and filaments. Cassette/detector plate: A light-proof housing for radiology film, containing front and back intensifying screens between which the film is placed. Collimation: This term refers to the process of adjusting an optical instrument so that the x-ray image includes the area of interest. Milliampere × second (mAs): Describes the exposure
setting of a radiology machine and determines the radiographic density. mAs is calculated by: Peak kilovoltage (kVp): The maximum voltage applied across an radiographic tube, which controls the x-ray penetration of the subject being imaged. Peak inspiration: Exposing film at peak inspiration maximizes the air in the lungs and the subject contrast within the thorax. Thoracic Radiographic ExposureFrom a technical standpoint, thoracic radiographic exposure should be obtained using a high peak kilovoltage (kVp) (80-120 kVp) and low milliampere-second (mAs) (1-5 mAs) technique. This technique allows for latitude (long gray scale) images, which are important when evaluating the structures of the thorax. Several examples would include:
For any dog measuring 15 cm or greater (measured at the liver or thickest part of the thorax), a grid (8:1, 110 lines per inch) should be used. Grids are available from most radiology manufacturers and a grid tray comes with all radiology units. For almost all radiology units, a grid is sold with the radiographic machine and table. The rotor for the anode and the low-voltage circuit for the focusing cup/electrons of the cathode should be coupled to a foot or hand switch so that accurate timing of the exposure at peak inspiration can be made (TABLE). Routine ViewsLateral ImagesPositioning
. Collimation
Remember to always include the sternum of the patient so as not to exclude vital anatomy:
Ventrodorsal ImagesPositioning
. The technique described in Step 2 does not work well for:
When presented with these types of patients ensure that the head and neck are straight out in front of the body and not obliqued to the left or right. Collimation
Dorsoventral ImagesPositioning & Collimation The dog is either in:
. Additional Views Humanoid Projection .
Horizontal Beam ProjectionsHorizontal beam sternal or dorsal projections are used for assessing the cranial mediastinum or fluid/air distribution within the thoracic cavity. These views are dependent on the ability of the radiology machine tube to be manipulated in a 90-deg angle. In addition, using a positioning trough makes these views easier to obtain.
. Quality ControlFor quality control of any diagnostic image, keep a simple 4-step approach in mind:
Technique & AnatomyGiven that the desired technique has been attained, make sure that the appropriate anatomy is included. The laterals, ventrodorsal, dorsoventral, humanoid, and horizontal beam projections should:
PositioningIf the technique exceeds quality standards and the correct anatomy is present, check patient positioning.
Positioning Veterinary Patients The following positioning devices can be used to help position patients and reduce staff members’ exposure to radiation:
. Patient in lateral recumbency showing correct use of tape and sandbags; the dog is muzzled due to its history of biting (see Dog Bites: Protecting Your Staff & Clients) Peak Inspiration for Image AcquisitionFinally, determine if the projection was taken at the peak of inspiration:
SummaryThoracic radiographs are often used as a first-line test for possible intrathoracic disease. High-quality, correctly positioned radiographs are required in order to provide as accurate an assessment as possible. In addition, a 3-view thorax (right lateral, left lateral, and dorsoventral or ventrodorsal view) is considered the standard of care in veterinary medicine. Following a consistent, repeatable pattern for obtaining thoracic radiographs ensures that the quality of the images will always be diagnostic. kVp = peak kilovoltage; mAs = milliampere × second The 3 Principles of Radiation SafetyX-rays are a form of electromagnetic radiation that has high-energy, high-frequency, and short-wavelength rays. These rays are classified as ionizing because they can create atomic ions or charged atoms, specifically in biological tissues (ie, animal and human tissue). Three basic principles should be adhered to when dealing with radiation and making radiographs:
These principles form the basis of a broader radiation safety concept called ALARA (As Low As Reasonably Achievable). TimeTime refers to the time the patient or the technician/veterinarian is exposed to primary (x-rays in the collimated beam directed toward the patient) or secondary (x-rays scattered away from the patient and outside the collimated field) radiation from the x-ray tube. Time can be minimized by:
DistanceThe principle of distance means that there needs to be physical distance between the technician/veterinarian and the patient/x-ray tube at the time of exposure.
The x-ray intensity will exponentially decrease as one doubles the distance from the primary source of radiation; in this case, the area of the collimated patient that is being imaged. If you can move from 2 to 4 feet away, you will have decreased the intensity of the scatter radiation by 25%. ShieldingShielding is required if you are staying in the room at time of exposure or within the walls of the room.
Lead shielding never protects the individual from primary radiation exposure (area inside the collimated light), only secondary or scatter radiation exposure. Radiation RegulationsRadiation safety requirements are specific to state regulations, so that a copy of the specific state radiation safety requirement for workers in veterinary medicine should be given to every staff member at the clinic as well as posted in the x-ray area. These regulations should be thoroughly reviewed with all employees on an annual basis. ALARA = as low as reasonably achievable; mA = milliampere; mAs = milliampere x second ReferencesSuggested Reading
Which evaluation criterion pertains to the AP axial projection lordotic position image of the chest?Chest Positioning. What is the proper patient position for the AP oblique projection of the chest to demonstrate the right lung?Patient position
Anterior (PA) oblique projections are obtained with patient upright with respective side of the chest rotated 45 degrees against the IR. The patient's arm that is closest to the cassette should be flexed, with the hand resting on the hip. The patient's opposite arm should be raised as high as possible.
Which ribs are more readily observed on an AP projection of the chest?The PA view specifically focuses on the anterior ribs. The rib series is often considered to be an unnecessary, unjustified projection in many radiology departments.
What vertebral joints are demonstrated with the AP axial projection?test
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