FAQ-General CT and MRI Issues

What are the patient weight and girth limits for different types of scanners?

Hospital CT Scanner MR Scanner PET-CT Scanner Gamma Camera Fluroscopy Table Interventional Radiology
Skagit Valley Hospital 450 lb, 70 cm bore 350 lb, 60 cm bore 450 lb, 70 cm bore 400 lb 350 lb 440 lb
Island Hospital 440 lb, 70 cm bore 350 lb, 60 cm bore NA 350 lb 500 lb 400 lb
Central Peninsula General Hospital 425 lb, 70 cm bore 350 lb, 60 cm bore NA 400 lb 330 lb NA

What are the indications for cervical spine CT in the setting of trauma?

The following clinical predictors of injury are appropriate criteria to evaluate patients with CT, rather than radiography.

Injury mechanisms:

  • High-speed motor vehicle accident: >35 mph combined
  • Motor vehicle accident with death at scene
  • Fall of >10 feet

Clinical evaluation:

  • Known closed head injury
  • Pelvic or multiple extremity fractures
  • Neurologic symptoms on physical exam
  • Cervical spine radiculopathy on physical exam
Reference: Julian A. Hanson, C. Craig Blackmore, Frederick A. Mann, and Anthony J. Wilson. Cervical Spine Injury: A Clinical Decision Rule to Identify High-Risk Patients for Helical CT Screening. Am. J. Roentgenol., Mar 2000; 174: 713 - 717.

What is the recommended imaging study for evaluation of pulmonary embolus in pregnant patients?

Computed tomography makes use of ionizing radiation, which should be avoided when possible, especially in pregnant patients, and especially in the first trimester of pregnancy. However, when absolutely necessary, pulmonary CTA (CT angiography) is the preferred method of radiologic evaluation for pulmonary embolus in pregnant patients, provided that no contra-indications to iodinated contrast are present. It is unlikely that a single CT examination will lead to serious adverse outcomes to the fetus. The use of iodinated contrast in pregnant patients has not been shown to be associated with adverse outcomes.

References:
1. McColl MD, Ramsay JE, Tait RC, et al. Risk factors for pregnancy associated venous thromboembolism. Thromb Haemost 1997;78:1183-8.
2. Gherman RB, Goodwin TM, Leung B, et al. Incidence, clinical characteristics, and timing of objectively diagnosed venous thromboembolism during pregnancy. Obstet Gynecol 1999;94:730-4.
3. Ros HS, Lichtenstein P, Bellocco R, et al. Pulmonary embolism and stroke in relation to pregnancy: how can high-risk women be identified? Am J Obstet Gynecol 2002;186:198-203.
4. British Thoracic Society Standards of Care Committee Pulmonary Embolism Guideline Development Group. British Thoracic Society guidelines for the management of suspected acute pulmonary embolism. Thorax 2003; 58: 470-483.
5. Hayashino Y, Goto M, Noguchi Y, Fukui T. Ventilation-perfusion scanning and helical CT in suspected pulmonary embolism: meta-analysis of diagnostic performance. Radiology 2005; 234: 740-748.
6. Quiroz R, Kucher N, Zou KH, Kipfmueller F, Costello P, Goldhaber SZ, Schoepf UJ. Clinical validity of a negative computed tomography scan in patients with suspected pulmonary embolism: a systematic review. JAMA 2005; 293: 2012-7.
7. Chan WS, Ray JG, Murray S, Coady GE, Coates, G, Ginsberg, JS. Suspected pulmonary embolism in pregnancy: Clinical presentation, results of lung scanning, and subsequent maternal and pediatric outcomes. Arch Intern Med 2002; 162: 1170-1175.
8. Winer-Muram HT, Boone JM, Brown HL, Jennings SG, Mabie WC, Lombardo GT. Pulmonary embolism in pregnant patients: fetal radiation dose with helical CT. Radiology. 2002; 224: 487-92.
9. Russell JR, Stabin MG, Sparks RB, et al. Radiation absorbed dose to the embryo/fetus from radiopharmaceuticals. Health Phys 1997; 73:756-769.
10. Hammer-Jacobsen E. Therapeutic abortion on account of x-ray examination during pregnancy. Danish Med Bull 1959; 6: 113-122.
11. Hall EJ. Radiobiology for the radiologist, 4th ed. Philadelphia: Lippincott; 1994: 363-452.
12. Wagner LK, Archer BR, Zeck OF. Conceptus dose from two state-of-the-art CT scanners. Radiology 1986; 159: 787-792.
13. Bushberg JT, Seibert JA, Leidholdt EM, Boone JM. The essential physics of medical imaging. Williams and Wilkins, Baltimore, 1994; 694.
14. Nelson JA, Livingston JC, Moon RG. Mutagenic evaluation of radiographic contrast media. Invest Radiol 1982; 17: 183-185.
15. Morisetti A, Tirone P, Luzzani F, de Haen C. Toxicologic safety assessment of iomeprol, a new x-ray contrast agent. Eur J Radiol 1994; 18 (Suppl 1): 21-31.
16. Ralston WH, Robbins MS, James P. Reproductive, developmental, and genetic toxicity of ioversol. Invest Radiol 1989; 24 (Suppl 1): 16-22.
17. desch F, Camus M, Ermans AM, et al. Adverse effects of amniofetography on fetal thyroid function. Am J Obstet Gynecol 1976; 126: 723-726.
18. na G, Zaffaroni M, Defilippi C, et al. Effects of iopamidol on neonatal thyroid function. Eur J Radiol 1992; 12: 22-25.
19. Webb JA, Thomsen HS, Morcos SK; Members of Contrast Media Safety Committee of European Society of Urogenital Radiology (ESUR). The use of iodinated and gadolinium contrast media during pregnancy and lactation. Eur Radiol 2005; 15: 1234-1240.

How do you decide if a patient is a suitable candidate for CT angiography examinations?

Studies have shown that interpretation of CTA examinations is limited by vessel calcifications. Patients with diabetes, coexisting cardiac disease, and age greater than 80 have been shown to have a sufficient degree of vascular calcifications that would limit CTA. Also, patients with certain degrees of renal insufficiency may be better served by an MRA examination rather than CTA.

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