Use of Ultrasound as an Alternative to CT

In light of concern over radiation dose in CT, it is helpful to remember that ultrasound is the imaging modality of choice for a number of abdominal, pelvic, and cardiovascular indications. Because ultrasound does not use ionizing radiation it is particularly useful in children and in women of child-bearing age when CT would otherwise expose the patient to pelvic radiation. This is particularly important in pregnancy (see The Pregnant Patient: Alternatives to CT and Dose-Saving Modifications to CT Technique). The following document illustrates scenarios for using ultrasound instead of CT.

Assessment of Pelvic Pain

Since ovarian cysts, hemorrhagic cysts, ovarian torsion, ectopic pregnancy, and pelvic inflammatory disease are all common etiologies of pelvic pain in women of reproductive age and are also well evaluated by ultrasound, ultrasound is the imaging modality of choice for assessing women with acute pelvic pain [1]. In addition to allowing for information regarding the uterus and adnexa in women, ultrasound can be used to assess the bowel (for example, for appendicitis [2]) and urinary tract (for example, for ureteral stones) in patients of both genders. Imaging of appendicitis is dependent on operator experience, with studies showing approximately 78% sensitivity and 83% specificity [3].

Assessment of Abdominal Pain

ACR appropriateness criteria rank ultrasound highest as the modality for initial imaging in patients with right upper quadrant pain, acute pancreatitis, severe abdominal pain with elevated lipase (without fever), and acute abdominal pain with jaundice [4,5,6]. Ultrasound is particularly helpful in detection of gallstones and biliary obstruction, as well as for the identification or exclusion of alternative diagnoses [7,8,9,10].

Assessment of Blunt Abdominal Trauma

In unstable trauma patients, a Focused Assessment with Sonography for Trauma (FAST) scan can be used to assess for free fluid [11]. This can quickly provide information that can support a decision to operate immediately, with the caveat that the false negative rate is at least 15% [12,13,14,15,16].

Assessment of Clinically Suspected Adnexal Mass

Ultrasound is the imaging modality of choice in assessing clinically suspected pelvic masses [17]. Ultrasound is used to determine the cystic or solid nature of the mass and to assess septations, solid elements, internal echogenicity, and vascularity that are used to predict if a mass is benign or malignant. These internal characteristics can be used to determine if an adnexal mass can be ignored, safely followed by ultrasound, or if surgery is warranted [18].

Cardiovascular Imaging

When an asymptomatic patient has a pulsatile abdominal mass and aortic aneurysm is suspected, ultrasound is the initial imaging modality of choice [19]. Population-based ultrasound screening studies have been recommended for male patients over the age of 65 [20]. For abdominal aortic aneurysms between 3 and 5.5cm in diameter, periodic imaging (typically with ultrasound) at 6- to 12- month intervals (dependent on rate of aneurysm enlargement on prior studies) is recommended [19].

In patients with acute or chronic chest pain and in patients with dyspnea of suspected cardiac origin, ultrasound (with or without pharmacologic stress, with or without transesophageal echocardiography) can be used to assess abnormalities of ventricular wall motion, pericardial effusion, valve dysfunction, cardiac thrombus, and aortic pathology such as dissection [21,22,23].

In patients with acute chest pain and suspected pulmonary embolism, ultrasound of the lower extremity can be utilized to assess for deep venous thrombosis, to aid in triage of patients to therapy, no therapy, or additional imaging [24].

In patients with suspected bacterial endocarditis, transesophageal echocardiography is the clinical reference standard. It can demonstrate vegetations on cardiac valves, valvular regurgitation, and perivalvular abscess [25].

Assessment of the extracranial carotid arteries is typically performed with ultrasound rather than CT. A recent meta-analysis shows that ultrasound has a higher sensitivity (89%) than does CTA (77%) for 70–99% stenosis [26].

Conclusion

The descriptions above are common examples of using ultrasound where CT might be considered as an alternative imaging modality. There are of course many other indications for ultrasound. The prudent use of ultrasound will allow for appropriate patient care and diminish unnecessary exposure of patients to ionizing radiation from CT.

References

1. Acute Pelvic Pain in the Reproductive Age Group. ACR Appropriateness Criteria®, American College of Radiology, 2015.
2. Right Lower Quadrant Pain — Suspected Appendicitis. ACR Appropriateness Criteria®, American College of Radiology, 2013.
3. Van Randen A, Bipat S, Zwinderman AH, et al. Acute Appendicitis: Meta-Analysis of Diagnostic Performance of CT and Graded Compression US Related to Prevalence of Disease. Radiology 2008; 249: 97-106.
4. Acute Pancreatitis. ACR Appropriateness Criteria®, American College of Radiology, 2012.
5. Jaundice. ACR Appropriateness Criteria®, American College of Radiology, 2012.
6. Right Upper Quadrant Pain. ACR Appropriateness Criteria®, American College of Radiology, 2013.
7. Hanbidge AE, Buckler PM, O'Malley ME Wilson SR. From the RSNA Refresher Courses: Imaging Evaluation for Acute Pain in the Right Upper Quadrant. Radiographics 2004; 24(4): 1117-1135.
8. Bennett GL, Balthazar EJ. Ultrasound and CT Evaluation of Emergent Gallbladder Pathology. Radiol Clin North Am 2003; 41(6):1203-1216.
9. Smith EA, Dillman JR, Elsayes KM, et al. Cross-Sectional Imaging of Acute and Chronic Gallbladder Inflammatory Disease. AJR 2009; 192(1): 188-196.
10. Laing FC, Federle MP, Jeffrey RB, Brown TW. Ultrasonic Evaluation of Patients With Acute Right Upper Quadrant Pain. Radiology 1981; 140(2): 449-455.
11. Blunt Abdominal Trauma. ACR Appropriateness Criteria®, American College of Radiology, 2012.
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16. Nural MS, Yardan T, Guven H, et al. Diagnostic Value of Ultrasonography in the Evaluation of Blunt Abdominal Trauma. Diagn Interv Radiol 2005; 11(1): 41-44.
17. Clinically Suspected Adnexal Mass. ACR Appropriateness Criteria®, American College of Radiology, 2012.
18. Levine D, Brown DL, Andreotti RF, et al. Management of Asymptomatic Ovarian and Other Adnexal Cysts Imaged on Ultrasound: Society of Radiologists in Ultrasound Consensus Conference Statement. Radiology 2010; 256(3): 943-954.
19. Pulsatile Abdominal Mass, Suspected Abdominal Aortic Aneurysm. ACR Appropriateness Criteria®, American College of Radiology, 2012.
20. Fleming C, Whitlock EP, Beil TL, Lederle FA. Screening for Abdominal Aortic Aneurysm: A Best-Evidence Systematic Review for the U.S. Preventive Services Task Force. Annals of Internal Medicine 2005; 142(3): 198-202.
21. Acute Chest Pain — Suspected Aortic Dissection. ACR Appropriateness Criteria®, American College of Radiology, 2016.
22. Dyspnea — Suspected Cardiac Origin. ACR Appropriateness Criteria®, American College of Radiology, 2010.
23. Chest Pain, Suggestive of Acute Coronary Syndrome. ACR Appropriateness Criteria®, American College of Radiology, 2014.
24. Acute Chest Pain — Suspected Pulmonary Embolism. ACR Appropriateness Criteria®, American College of Radiology, 2016.
25. Suspected Infective Endocarditis. ACR Appropriateness Criteria®, American College of Radiology, 20014.
26. Chappell FM, Wardlaw JM, Young GR, et al. Carotid Artery Stenosis: Accuracy of Noninvasive Tests--Individual Patient Data Meta-Analysis. Radiology 2009; 251(2): 493-502.