# Synthetic interpolated DSA for radiation exposure reduction via gamma variate contrast flow modeling: a retrospective cohort study

## TL;DR

This study shows that reducing the frame rate of digital subtraction angiography by 75% using a new algorithm does not affect diagnostic quality, thus lowering patient radiation exposure.

## Contribution

A novel gamma variate model-based interpolation technique enables 75% frame rate reduction in DSA without compromising diagnostic accuracy.

## Key findings

- GVM reconstructions at 75% frame rate reduction achieved average voxel errors of 27 ± 2% in anteroposterior projections.
- Reader studies showed diagnostic quality was preserved at 75% frame rate reduction with a high Subjective Image Grading Scale rating.
- The technique can be applied to other angiography studies beyond cerebral vasculature evaluation.

## Abstract

Digital subtraction angiography (DSA) yields high cumulative radiation dosages (RD) delivered to patients. We present a temporal interpolation of low frame rate angiograms as a method to reduce cumulative RDs.

Patients undergoing interventional evaluation and treatment of cerebrovascular vasospasm following subarachnoid hemorrhage were retrospectively identified. DSAs containing pre- and post-intervention runs capturing the full arterial, capillary, and venous phases with at least 16 frames each were selected. Frame rate reduction (FRR) of the original DSAs was performed to 50%, 66%, and 75% of the original frame rate. Missing frames were regenerated by sampling a gamma variate model (GVM) fit to the contrast response curves to the reduced data. A formal reader study was performed to assess the diagnostic accuracy of the “synthetic” studies (sDSA) compared to the original DSA.

Thirty-eight studies met inclusion criteria (average RD 1,361.9 mGy). Seven were excluded for differing views, magnifications, or motion. GVMs fit to 50%, 66%, and 75% FRR studies demonstrated average voxel errors of 2.0 ± 2.5% (mean ± standard deviation), 6.5 ± 1.5%, and 27 ± 2%, respectively for anteroposterior projections, 2.0 ± 2.2%, 15.0 ± 3.1%, and 14.8 ± 13.0% for lateral projections, respectively. Reconstructions took 0.51 s/study. Reader studies demonstrated an average rating of 12.8 (95% CI 12.3−13.3) for 75% FRR, 12.7 (12.2−13.2) for 66% FRR and 12.0 (11.5−12.5) for 50% FRR using Subjective Image Grading Scale. Kendall’s coefficient of concordance resulted in W = 0.506.

FRR by 75% combined with GVM reconstruction does not compromise diagnostic quality for the assessment of cerebral vasculature.

Using this novel algorithm, it is possible to reduce the frame rate of DSA by as much as 75%, with a proportional reduction in radiation exposure, without degrading imaging quality.

• DSA delivers some of the highest doses of radiation to patients.

• Frame rate reduction (FRR) was combined with bolus tracking to interpolate intermediate frames.

• This technique provided a 75% FRR with preservation of diagnostic utility as graded by a formal reader study for cerebral angiography performed for the evaluation of cerebral vasospasm.

• This approach can be applied to other types of angiography studies.

The online version contains supplementary material available at 10.1186/s41747-023-00404-2.