Computerized Tomography

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Contents 1 More Specific Terms 2 Indications 3 Contraindications 4 Procedure 5 Complications 6 More General Terms 7 References

More Specific Terms

• cardiac computed tomography angiography; non-invasive coronary artery imaging; CT angiography (CCTA)
• computed tomography angiography (CT angiography)
• coronary artery calcium (CAC testing)
• single photon emission computed tomography (SPECT)
• virtual (CT) colonoscopy (CT colonography)
• whole-body computerized tomography (CT)

Indications

• (clinical indications for CT)
• examination of intracranial structures ( MRI is the imaging modality of choice)

• intracranial bleed

• epidural, subdural, intracerebral ( subarachnoid)

• intracranial tumors
• head CT delivers > 100 mGy of X-rays [3]
• head CT during development may affect cognition [3]

• skeletal trauma

• head injury

• skull fracture
• epidural or subdural hematoma

• fractures of the vertebral column
• fractures of pelvic bones

• especially fracture- dislocation of the acetabulum

• localization & staging of tumors

• localization of brain tumors
• staging of tumors of the larynx
• staging of GI tumors

• carcinoma of the esophagus
• carcinoma of the stomach
• colorectal carcinoma

• pelvic tumors ( MRI may be imaging modality of choice)

• endometrial carcinoma
• ovarian cancer
• cancer of the bladder
• prostate cancer

• high-resolution CT is the imaging modality of choice for bronchiectasis
• helical CT may be useful diagnosis of pulmonary embolism
• assessment of ectopic/dystrophic calcification

• coronary artery calcification [4]

• non-invasive coronary artery imaging ( CT angiography) [5]

Contraindications

• caution for procedures using contrast agent

• discontinue metformin 48 hours prior to procedure
• consider Mucomyst

Procedure

• CT images are obtained by computed reconstruction from measurements of differential X-ray absorbtion obtained through an angle of 360 degrees. These measurements obtained by electronic detection allow calculation of radiographic densities at any point in plane represented as pixels in the CT software. Conventional CT examines 8-10 mm slices obtained at 10 mm intervals. High-resolution CT (HRCT) examines 1-2 mm slices & delineates detail that convention CT does not. Helical or spiral CT allows 3-dimensional data acquistion & reduces motion artifact.

Complications

• radiation exposure:

• abdominal CT delivers 50-fold more radiation than plain films [6]
• exposure to about 9-10 mSv of radiation with CT of the neck, chest, abdomen, or pelvis [8]
• 1 cancer per 1000 patients receiving 10 mSv of radiation [8]
• radiation exposure from CT may cause 1.5-2% of cancers in USA [6]

• x-rays used during CT examinations may cause some implanted & external electronic medical devices to malfunction (most patients with electronic medical devices undergo CT scans without any adverse consequences) [7]

More General Terms

• radiography (diagnostic imaging, roentgenography)

References

1. Introduction to Clinical Imaging, Radiology Syllabus, UCSF, 1993
2. Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998
3. Journal Watch 24(4):34, 2004 Hall P et al, Effect of low doses of ionising radiation in infancy on cognitive function in adulthood: Swedish population based cohort study. BMJ 328:19, 2004 PMID: [1]
   - Hall P et al [2]
4. Journal Watch 24(5):37, 2004 Greenland P et al, Coronary artery calcium score combined with Framingham score for risk prediction in asymptomatic individuals. JAMA 291:210, 2004 PMID: [3]
5. van Mieghem CAG et al, Multislice spiral computed tomography for the evaluation of stent patency after left main coronary artery stenting: A comparison with conventional coronary angiography and intravascuscular ultrasound. Circulation 2006, 114:645 PMID: [4]
   - Kimmelstiel C, Multislice computed tomography after left main drug-eluting stenting: Are we putting the CarT before the horse? Circulation 2006, 114:616 PMID: [5]
6. Brenner DJ and Hall EJ Computed tomography - An increasing source of radiation exposure. N Engl J Med 2007, 357:2277 PMID: [6]
7. FDA MedWatch [7]
8. Griffey RT and Sodickson A. Cumulative radiation exposure and cancer risk estimates in emergency department patients undergoing repeat or multiple CT. AJR Am J Roentgenol 2009 Apr; 192:887. PMID: [8]
9. National Guideline Clearinghouse ACR practice guideline for the performance of high-resolution computed tomography (HRCT) of the lungs in adults. American College of Radiology (ACR) ngc-guideline: [9]
   - ACR-ASNR practice guideline for the performance of computed tomography (CT) of the brain. ngc-guideline: [10]

computerized tomography (CT)