Computed tomography (CT) scan, performed with contrast enhancement, is one of the most commonly requested examinations in diagnostic imaging. In a patient with an elevated creatinine or an allergy to contrast agents, the scan may be performed without the benefit of contrast enhancement. Ultrasound (US), performed with contrast agent enhancement does not have any nephrotoxicity and may be performed on patients with CT contrast allergy. The investigators propose that US with Contrast enhanced ultrasound (CEUS) is superior to unenhanced CT scan in this population.

Contrast enhanced computed tomography (CT) is one of the most common investigations performed in any radiology department, used widely in evaluating pathology in any part of the body.

Historically, it is well known that the use of contrast agents for CT scans may result in nephropathy, or renal failure. Nephrotoxicity associated with the injection of CT contrast agents may occasionally occur in healthy individuals and more commonly in those with borderline renal function. If abnormal kidney function is known to exist in a patient sent for CT scan, the examination is performed without the valuable assistance of contrast enhancement. Further, if prior hypersensitivity to the contrast agent for CT scan is known, again, the scan will be performed without the use of contrast agent.

Ultrasound (US) performed conventionally in grayscale and with Doppler is able to evaluate most abdominal and pelvic organs and also provides vascular information related to large vessel blood flow. Contrast enhanced ultrasound (CEUS) provides more precise information on blood flow than is available with Doppler and has been shown to be comparable to CT scan in some circumstances. We believe that a comparison of conventional US, with CEUS, and unenhanced CT scan would clearly favor ultrasound for detection of soft tissue pathology on the basis of its inherent tissue contrast differentiation.

Inclusion Criteria:

• unenhanced CT scan of abdomen
• known renal compromise
• known hypersensitivity to CT contrast agents

Exclusion Criteria:

• CT scan performed with contrast agent

Patients referred for unenhanced CT scan on the basis of renal compromise of CT contrast agent sensitivity will be eligible for recruitment for our study.