Time-resolved angiography for the assessment of central venous anatomy and patency

Author(s): Dr Lynne Armstrong, Christopher B Lawton, Dr Nathan Manghat

Hospital: Bristol Heart Institute, Bristol Royal Infirmary

Reference: RAD Magazine, 41, 484, 24-26

Excerpt: 

Time-resolved angiography with interleaved stochastic trajectories (TWIST) is a magnetic resonance angiography (MRA) technique which creates a series of rapid multiplanar data sets with good spatial resolution. Rapid successive measurements enabled by temporal acceleration reduce the reliance on precision of bolus timing to ensure maximum intravenous contrast within the vascular system.

This imaging technique generates a series of imaging datasets from neck to groin at different time points of the same intravenous contrast bolus (unenhanced, pulmonary venous, systemic arterial, early systemic venous and late systemic venous). This permits comprehensive assessment of the arterial and venous vasculature without the excessive influence of dynamic variables such as haemodynamics and the skill of the individual operator. Time-resolved methods are faster with improved temporal resolution at the expense of some spatial resolution. They use a conventional T1 weighted gradient echo sequence with scan time per volume of only a few seconds, which allows multiple repetitions over a short period. Using thicker, fewer slices is one method by which this is achieved. By increased efficiency of k space data storage they also allow more rapid sampling, which is critical for the excellent contrast resolution necessary for successful MRA. Such rapid successive measurements make timing of the contrast less critical, so minimising variance in bolus timings and also permitting the use of smaller contrast volumes, which is desirable on the basis of cost and reducing the perceived risk of nephrogenic systemic fibrosis. TWIST also gives spatial information that is comparable with conventional contrast-enhanced MR angiography while allowing dynamic information previously only available with digital subtraction angiography (DSA) or intravascular ultrasound.

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