splitbolus

Split bolus is a radiology technique in which the total iodinated contrast dose is divided into two injections separated by a delay, allowing two phases of enhancement to be captured in a single CT acquisition. The goal is to optimize visualization of both vascular and excretory structures, or to obtain arterial and venous information without multiple scans, thereby reducing contrast load and radiation exposure.

In practice, split bolus is typically performed with a dual-head injector or two IV lines. A first bolus (commonly about 40–70 mL of contrast) is given at a rate of 3–5 mL per second, followed by a saline flush. After a protocol-dependent delay, a second bolus of a similar volume is administered. The CT scan is then acquired at a timing window designed to maximize the desired combination of enhancement, often around 60–90 seconds after the second injection, though exact timing varies with protocol and scanner. In CT urography, this approach aims to separate nephrographic/parenchymal enhancement from excretory-phase opacification of the urinary tract within one examination.

Applications include CT urography and certain CT angiography protocols where simultaneous arterial and venous or urinary tract visualization is beneficial. Advantages include reduced total contrast dose and fewer acquisitions, with potential lower radiation exposure. Limitations involve the need for careful timing and protocol adherence; mis-timing can lead to suboptimal enhancement. Patient factors such as renal function, cardiac status, and body habitus influence suitability and specifics of the protocol. See also CT angiography, CT urography, and intravenous contrast administration.