noncontrast

Noncontrast refers to imaging studies conducted without the administration of contrast agents. In radiology, this term most often applies to computed tomography (CT) and magnetic resonance imaging (MRI), as well as to some vascular and ultrasound techniques that can be performed without contrast.

Noncontrast CT (NCCT) is widely used in acute settings because it is fast and readily available. It evaluates for intracranial hemorrhage, calcifications, stones, and other hyperdense processes, and it is often the initial study before contrast-enhanced CT or thrombolytic therapy. Attenuation is measured in Hounsfield units to differentiate tissues; NCCT provides limited soft tissue contrast and does not reliably characterize lesions that require enhancement.

Noncontrast MRI uses standard sequences such as T1- and T2-weighted images, FLAIR, diffusion-weighted imaging (DWI), and susceptibility-weighted imaging (SWI). DWI is particularly important for identifying acute ischemia. Noncontrast MRI can be chosen when gadolinium or other contrast agents are contraindicated, as in kidney disease or contrast allergy. Vascular imaging can be performed without contrast using time-of-flight MR angiography (TOF-MRA).

Limitations of noncontrast imaging include reduced ability to assess vascular structures and lesion vascularity, and in CT the exposure to ionizing radiation remains a consideration. When the information required is vascular detail or enhancement patterns, contrast-enhanced studies are preferred.

Noncontrast studies are accordingly selected to balance diagnostic yield, safety, and patient factors.

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