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1083.e2 Computed Tomography Scan

Computed Tomography Scan Client Education
Sheet
VetBooks.ir Difficulty level: ♦♦♦ Equipment, Anesthesia Anticipated Time

Synonyms • CT scanner The time required to perform the study will
depend on the CT scanner used and the study
• Anesthesia/restraint equipment
CT scan, CAT scan, computed axial tomography ○ General anesthesia is generally required. to be performed and therefore varies. Most scans
CT studies are relatively brief, and gas will be completed in 10-30 minutes, including
Overview and Goal anesthesia or a constant rate infusion of time for anesthetic induction.
Computed tomography (CT) is a method of intravenous (IV) anesthetic agent (gener- Example: CT scan of the brain:
cross-sectional imaging that involves ionizing ally propofol) can be used for the study. • Two scans are performed, one before contrast
radiation. When compared to radiography, The equipment needed is determined by injection and one after contrast injection.
CT allows improved evaluation of areas of the type of anesthesia used. • The time for each of these studies may
complex anatomy by avoiding superimposition ■ Gas anesthesia: endotracheal tube and vary from 5-10 minutes (older, single-slice
of multiple structures and provides improved laryngoscope for placement, anesthesia translational scanners) to less than 30 seconds
contrast resolution of tissues. CT can be used machine; no special requirements (new multislice helical scanners).
for assessing any area of the body. In veterinary (unlike magnetic resonance imaging • Complex scans of large areas (abdomen or
medicine, common uses include assessment [MRI]) entire body for example) may require a pause
of the head (nasal cavity, auditory apparatus), ■ Ventilator use to facilitate breath holds in the scanning to allow the x-ray tube to
cervical soft tissues, thorax, abdomen, spine, and offers optimal thoracic image quality. cool. Generally, this pause is relatively short
skeletal structures (e.g., complex fractures, elbow ■ Constant rate infusion: IV infusion (e.g., 2-3 minutes), but it must be considered
dysplasia). It is also often used for planning pump when estimating the total general anesthesia
of surgery and radiation therapy. In recent ○ VetMousetrap for restraint of awake cats time for the patient.
years, CT has become increasingly available ○ Monitoring equipment
in private practice and is being more routinely ■ Pulse oximeter Preparation: Important
performed. It may be more time and cost- ■ Electrocardiogram (ECG) Checkpoints
efficient to use CT imaging in place of other • Emergency kit: as with any procedure Preparation for general anesthesia:
types of multimodal imaging (e.g., CT scan of performed under general anesthesia, the • Routine preanesthetic fasting
thorax and abdomen may be more cost-effective equipment and drugs necessary for emer- • Place IV catheter: when placing the catheter,
than thoracic and abdominal radiographs with gency resuscitation of the patient should be the anticipated position of the patient
abdominal ultrasound). immediately available. within the CT gantry must be considered
• IV contrast agent and the catheter placed to allow easy access
Indications ○ Iodinated contrast agent labeled for IV to it during the procedure. For example, in
• Disease of the central nervous system use (i.e., diatrizoate/metrizoate compounds patients undergoing CT scan of the head, it
• Disease of the nasal cavity/upper airway/ such as Renografin 60, iohexol [Omni- is convenient to have the IV catheter placed
auditory apparatus paque], iopamidol [Isovue]) in the saphenous vein, although the forelimb
• Evaluation for pulmonary metastasis or • IV fluids (optional) can be extended caudally for ease of access
other pulmonary parenchymal disease • Heating pad/blankets (optional) if the catheter is in a cephalic vein.
(more sensitive than radiographs), including
pulmonary thromboembolism (CT contrast
angiogram)
• Evaluation of abdominal masses, the urinary
tract (e.g., ectopic ureters), and hepatic/portal
venous system (e.g., portosystemic shunts)
• Evaluation of complex fractures for surgical
planning
• Evaluation for developmental orthopedic
disease: elbow dysplasia, tarsal osteochon-
dritis dissecans (OCD)
• Determine the extent of tumor involvement R L R L
for surgical planning.
• Radiation therapy planning (used with
specialized planning software)
Contraindications
• Inability to tolerate general anesthesia
○ If fast multislice imaging is available, it is
feasible to perform CT in many awake or A B
lightly sedated patients that cannot tolerate
general anesthesia. A restraint device for COMPUTED TOMOGRAPHY SCAN CT images from a normal (A) and abnormal (B) canine nasal cavity.
use on awake cats is commercially available CT is based on the principle of differential attenuation of tissues, and as in radiographs, bone appears white,
(VetMousetrap). air appears black, and soft tissues are intermediate in appearance. The term density is used for describing the
• Presence of large metallic implants in the appearance of tissues in CT images. In the normal patient, the nasal turbinates and nasal septum are present and
surrounded by air. In the abnormal patient, the left half of the nasal cavity is filled with material of soft-tissue
area of interest does not contraindicate the density, and there is loss (destruction) of the nasal turbinates. The nasal septum is thinned and deviated to the
procedure, but the information offered by right. The right half of the nasal cavity is normal in appearance, which is considered evidence of an aggressive
the study will be limited by the presence of process in the left half of the nasal cavity. Differentials for aggressive processes include neoplasia and fungal
artifact. rhinitis. In this case, neoplasia is considered likely based on the mass effect within the nasal cavity.

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