Cardiac/Thoracic Systems and Abdomen/Pelvis Conditions

Summary of Ordering Guidelines (Cardiac/ Thoracic Systems and Abdomen/Pelvis Conditions)

The following summaries are based on the Canadian Association of Radiologists Diagnostic Imaging Referral Guidelines ( Physicians are encouraged to consult the full guidelines for more detailed information on recommended imaging for the wide range of patient conditions.


Cardiac/ Thoracic Systems and Abdomen/Pelvis Conditions


Cardiac/Thoracic Systems

CT is most frequently preferred over MRI because of the improved spatial resolution (CT = 0.4mm. versus MRI = 6mm).

MRI is preferred over CT only for tissue characterization, particularly solid versus cystic or fatty. MRI may be useful in detection of tumor invasion into mediastinal structures or chest wall.

In patients with severe CT contrast reactions or in situations where ionizing radiation should be limited (very young or pregnant patients), MR may be considered rather than CT.  However, the benefit of MR relative to CT is limited in the thorax and in most situations a low dose CT or a CT with IV contrast will be preferable to an MRI.

Depending on the cardiovascular condition in question usually referral to a specialist consultant is most appropriate before the advanced CT or MRI imaging is requested. All conditions of acute cardiovascular compromise should be referred to an appropriate Emergency Department (e.g. aortic dissection, sepsis, postsurgical complication or known congenital heart disease). Many chronic cardiovascular diseases remain under the care of a specialist or specialist clinic (e.g. aortic aneurysms, connective tissue disorders, CHF, congenital heart diseases).

While echocardiography remains the cardiac imaging workhorse, the following conditions may require the primary care usage of cardiac CT or MRI.

Cardiac CT:

  1. Possible cardiac masses or pericardial disease seen on chest x-ray or echocardiography
  2. Suspected congenital anomalies. (e.g. vascular rings, coarctations, or aortic aneurysms, left ventricular hypertrophy, right heart disorders .)
  3. Coronary calcium scoring has a documented value when used to adjust intermediate risk score patients (Risk score 8 to 20) either to a higher or lower category.
  4. Coronary CT Arteriography:
    1. Certain patient parameters have been shown to adversely affect the diagnostic performance of 64-slice CCTA: coronary calcification, high heart rate, heart rate variability and body mass index.
    2. Positive predictive value is lower in populations with low disease prevalence.
    3. It should be recognized that CCTA assesses the anatomy of the coronary tree and does not provide information as to the functional relevance of the stenosis.
    4. Symptomatic patients with low to intermediate pre-test probability of obstructive coronary artery disease who would otherwise be considered for conventional coronary angiography. This would typically be patients with chest pain and an equivocal or uninterpretable stress test.
    5. Patients at low to intermediate risk of coronary artery disease with planned surgery for valvular or structural heart disease who would otherwise require pre-operative conventional coronary angiography.
  5. Follow up of chronic disorders. (e.g. ascending arch aneurysms, coarctation)

Cardiac MRI is essentially a subspecialty imaging modality; normally the patient would already be under the care of a subspecialist. Primary care personnel may order Cardiac MRI on direction of a specialist. Careful review of Cardiac MRI imaging indications leaves only the documentation of lesions suspected of being benign cystic or fatty on CT as a reason for referral.


Abdomen/Pelvis Conditions

CT is ALWAYS preferred initially over MRI for the following indications:

  1. Investigation of abdominal pain
  2. Evaluate for source of fever and infection not yet diagnosed
  3. Detection and characterization of focal lesions in solid organs
  4. Staging of Malignancy
  5. Diagnosis and follow-up of pancreatitis (or complications there of) 6. Work-up of acute bowel disorders including: Acute appendicitis (except in the setting of pregnancy), bowel obstruction, infectious, ischemic, inflammatory bowel
  6. Trauma
  7. Characterization of indeterminate adrenal masses
  8. Rule out intra-peritoneal or retroperitoneal hemorrhage
  9. Detection and characterization of intra-abdominal fluid collections
  10. Evaluation of complications following pelvic surgery, including abscess, urinoma, & lymphocele

Ultrasound (US) is ALWAYS preferred initially over MRI for the following indications:

  1. Biliary colic and symptoms and signs of biliary tree obstruction and pathology
  2. Pain not yet diagnosed
  3. Per vaginal bleeding and pelvic pain
  4. Detection and characterization of adnexal and uterine masses
  5. Testicular pathology
  6. Work up or characterization of occult genitourinary congenital anomalies
  7. Renal colic, obstructive renal symptoms, and hematuria
  8. Rule out intra-peritoneal or retroperitoneal hemorrhage
  9. Detection and characterization of intra-abdominal fluid collections
  10. Evaluation of complications following pelvic surgery, including abscess, urinoma, & lymphocele

MRI may be useful for the following indications almost always AFTER initial diagnostic information is provided by CT or US, but please note that wait time will vary on a case-by-case basis with the strength of the indication (relevant details from the history, physical examination and laboratory studies will greatly assist the triaging radiologist):

  1. Findings requiring clarification from other imaging studies or laboratory values
  2. Characterization of parenchymal lesions detected on other imaging modalities
  3. Tumour staging and/or evaluation of treatment response
  4. Investigation of biliary ductal pathology and ductal anomalies including choledocholithiasis and primary sclerosiing cholangitis
  5. Assessment of inflammatory bowel disease
  6. Detection and staging of prostate cancer
  7. Characterization of adnexal and uterine pathology, including: Neoplams, endometriosis, adenomyosis, fibroids, & congenital abnormalities
  8. Assessment of fetal and placental abnormalities
  9. Identification of the source of lower abdominal pain in pregnant women, including appendicitis and ovarian and uterine masses
  10. Assessment of gynecological emergencies (ectopic pregnancy, ovarian torsion, pelvic inflammatory disease / abscess)
  11. Determination of arterial and venous anatomy and patency
  12. Known or suspected congenital abnormalities

* MRI may be useful in patients in who iodinated contrast is contraindicated.

Depending on the condition in question, it may still be most appropriate to refer a patient for a consultant’s opinion prior to requesting an imaging procedure. Please consider the following common abdominal and pelvic requests from this perspective:

  1. Investigation of inflammatory bowel disease and perianal disease
  2. Work up of extent of prostate cancer
  3. Staging and follow-up of certain malignancies