Contents

Search

computerized tomography (CT)

Indications: 1) examination of intracranial structures (MRI is the imaging modality of choice) a) intracranial bleed - epidural, subdural, intracerebral (subarachnoid) b) intracranial tumors 2) skeletal trauma a) head injury - skull fracture - epidural or subdural hematoma b) fractures of the vertebral column c) fractures of pelvic bones - especially fracture-dislocation of the acetabulum 3) localization & staging of tumors a) localization of brain tumors b) staging of tumors of the larynx c) staging of GI tumors - carcinoma of the esophagus - carcinoma of the stomach - colorectal carcinoma d) pelvic tumors (MRI may be imaging modality of choice) - endometrial carcinoma - ovarian cancer - cancer of the bladder - prostate cancer 4) high-resolution CT is the imaging modality of choice for bronchiectasis 5) helical CT may be useful diagnosis of pulmonary embolism 6) assessment of ectopic/dystrophic calcification -> coronary artery calcification [4] 7) non-invasive coronary artery imaging (CT angiography) [5] Contraindications: - caution for procedures using contrast agent a) discontinue metformin 48 hours prior to procedure b) consider Mucomyst - presence of insulin pump, cardiac implantable electronic device*, or neurostimulator should NOT preclude performance of an appropriate, medically indicated CT scan [15] * pacemaker, implantable cardioverter defibrillator 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 - radiographic densities are measured in Hounsfield units - 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 - contrast is generally used to identify vasculature or the gastrointestinal tract - Naeotom Alpha CT utilizes photon-counting detectors that can count individual x-ray photons that pass through a patient & discriminate their energy [18] - current CT imaging systems are capable of measuring cumulative energy from numerous x-rays at once - photon-counting CT scan can reduce radiation exposure for patients & the need for contrast agents. - photon-counting CT scan can work with images that visualize even very fine tissue structures, such as the smaller bronchi of the lungs or metastases in bones [18] Complications: - radiation exposure: a) head CT delivers > 100 mGy of X-rays [3] - head CT during development may affect cognition [3] b) abdominal CT delivers 50-fold more radiation than plain films [6] c) exposure to about 9-10 mSv of radiation with CT of the neck, chest, abdomen, or pelvis [8]; 5-7 mSv [2] d) 1 cancer per 1000 patients receiving 10 mSv of radiation [8] e) radiation exposure from CT may cause 1.5-2% of cancers in USA [6] f) 30 solid tumors per 10,000 scans in girls & about 14 in boys [12] g) radiation from childhood CT increase risk for brain tumors & leukemia [9] - 2-3 head CTs in children under age 15 years may triple risk for brain tumors - 5-10 CTs may triple risk for leukemias - absolute risk is small - 1 excess leukemia & 1 excess brain tumor per 10,000 head CTs before age 10 [9] - relative risk = 1.24 [11] h) higher rates of cancer in children who underwent computed tomography than in those who did not [17] i) 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] j) patients rarely warned about radiation hazzards from CT scans [13] k) use of CT in children is diminishing [14] - no evidence of contrast nephropathy from contrast agents used in computed tomography [16]

Related

Hounsfield units (HU)

Specific

cardiac computed tomography angiography; coronary computed tomography angiography; CT angiography (CCTA) computed tomography angiography (CT angiography) CT enterography; computed tomography enterography CT for placement of radiation therapy fields CT guidance for procedure CT of abdomen CT of abdomen & pelvis CT of adrenal gland CT of ankle CT of calcaneus CT of cervical & lumbar spine CT of cervical & thoracic spine CT of cervical spine CT of chest & abdomen & pelvis CT of chest; CT of thorax CT of clavicle CT of elbow CT of face & neck (soft tissues) CT of facial bones & maxilla CT of facial bones & sinuses CT of femur CT of foot CT of forearm CT of hand CT of head CT of head & cervical spine CT of head & mandible CT of head & maxillofacial region CT of head & neck CT of head & temporal bone CT of hip CT of kidney CT of knee CT of liver CT of lower extremity CT of lower leg CT of lumbar spine CT of lumbar spine & sacrum CT of neck & superior mediastinum CT of neck (soft tissues) CT of orbit, sella, posterior fossa, or ear CT of pancreas CT of pelvis CT of pelvis & lower extremity CT of posterior fossa CT of sacroiliac joint CT of sacrum CT of sacrum & coccyx CT of scapula CT of sella turcica CT of shoulder CT of sinus CT of sinuses & mandible CT of spine; CT of vertebral column CT of spleen CT of temporomandibular joint (TMJ) CT of thoracic & lumbar spine CT of thoracic spine CT of thumb CT of toe CT of upper extremity CT of wrist electromagnetic navigation MRI of temporomandibular joint (TMJ) optical coherence tomography (OCT) single photon emission computed tomography (SPECT) virtual (CT) colonoscopy (CT colonography) whole-body computerized tomography (CT)

General

tomography

References

  1. Introduction to Clinical Imaging, Radiology Syllabus, UCSF, 1993
  2. Medical Knowledge Self Assessment Program (MKSAP) 11, 16. American College of Physicians, Philadelphia 1998, 2012
  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: 14703539 - Hall P et al http://bmj.bmjjournals.com/cgi/content/full/328/7430/19
  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: 14722147
  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: 16894038 - Kimmelstiel C, Multislice computed tomography after left main drug-eluting stenting: Are we putting the CarT before the horse? Circulation 2006, 114:616 PMID: 16908783
  6. Brenner DJ and Hall EJ Computed tomography - An increasing source of radiation exposure. N Engl J Med 2007, 357:2277 PMID: 18046031
  7. FDA MedWatch http://www.fda.gov/medwatch/safety/2008/safety08.htm#ElectronicMedical
  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: 19304691
  9. Pearce MS et al Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study The Lancet, Early Online Publication, 7 June 2012 PMID: 22681860 http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)60815-0/abstract - Einstein AJ Beyond the bombs: cancer risks of low-dose medical radiation The Lancet, Early Online Publication, 7 June 2012 PMID: 22681861 http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)60897-6/fulltext
  10. Smith-Bindman R, Lipson J, Marcus R et al Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer. Arch Intern Med. 2009 Dec 14;169(22):2078-86 PMID: 20008690
  11. Mathews JD et al Cancer risk in 680,000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians. BMJ 2013;346:f2360 PMID: 23694687 http://www.bmj.com/content/346/bmj.f2360 - Sodickson A CT radiation risks coming into clearer focus. BMJ 2013;346:f3102 PMID: 23694689 http://www.bmj.com/content/346/bmj.f3102
  12. Miglioretti DL et al The Use of Computed Tomography in Pediatrics and the Associated Radiation Exposure and Estimated Cancer Risk. JAMA Pediatr. 2013;():1-8. June 10, 2013 PMID: 23754213 http://archpedi.jamanetwork.com/article.aspx?articleid=1696279 - Schroeder AR and Redber RF The Harm in Looking JAMA Pediatr. 2013;():1-3. June 10, 2013 PMID: 23753832 http://archpedi.jamanetwork.com/article.aspx?articleid=1696281
  13. Young K, Fairchild DG, Di Francesco L Patients Rarely Warned About Radiation Hazards from CT Imaging Physician's First Watch, Jan 28, 2015 David G. Fairchild, MD, MPH, Editor-in-Chief Massachusetts Medical Society http://www.jwatch.org - Consumer Reports. Jan 27, 2015 The surprising dangers of CT scans and X-rays. Patients are often exposed to cancer-causing radiation for little medical reason, a Consumer Reports investigation finds. http://www.consumerreports.org/cro/magazine/2015/01/the-surprising-dangers-of-ct-sans-and-x-rays/index.htm
  14. Parker MW et al Computed Tomography and Shifts to Alternate Imaging Modalities in Hospitalized Children. Pediatrics. August 24, 2015. PMID: 26304828 http://pediatrics.aappublications.org/content/early/2015/08/18/peds.2015-0995
  15. FDA Safety Alert. April 1, 2016 Interference between Computed Tomography (CT) and Electronic Medical Devices: Notification - Current Understanding of Potential Risk. http://www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm493739.htm - FDA, Radiation-Emitting Products Interference between CT and Electronic Medical Devices.
  16. Hinson JS, Ehmann MR, Fine DM et al. Risk of acute kidney injury after intravenous contrast media administration. Ann Emerg Med 2017 Jan 19 PMID: 28131489 - Aycock RD et al. Acute kidney injury after computed tomography: A meta-analysis. Ann Emerg Med 2017 Aug 12 PMID: 28811122
  17. Hong JY, Han K, Jung JH, Kim JS. Association of exposure to diagnostic low-dose ionizing radiation with risk of cancer among youths in South Korea. JAMA Netw Open 2019 Sep 4; 2:e1910584. PMID: 31483470 https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2749234
  18. Ingram I FDA Clears 'Major Advancement' in CT Imaging. New Siemens; CT scanner is first allowed by agency with photon-counting detectors. MedPage Today September 30, 2021 https://www.medpagetoday.com/radiology/diagnosticradiology/94793 - FDA News Release. September 30, 2021 FDA Clears First Major Imaging Device Advancement for Computed Tomography in Nearly a Decade. https://www.fda.gov/news-events/press-announcements/fda-clears-first-major-imaging-device-advancement-computed-tomography-nearly-decade

Images

image related to computerized tomography (CT)