I’m going to admit this up front, this article is extremely boring if read all at once. Please, the intention here is to create a reference. Lot’s of table and rote learning. I’m sorry. Good luck 😅

Digital Subtraction Angiography (DSA) achieves high vascular contrast by removing background anatomy through temporal subtraction.

While this technique greatly enhances vessel visibility, it is also highly sensitive to any inconsistencies between the mask and live images. These inconsistencies lead to artefacts, which may mimic or obscure pathology. Understanding their physical causes allows radiologists and technologists to recognise and minimise them in practice.

Pass your radiology physics exam first time

I’ve separated the artefacts in four main categories: motion, contrast, detector and processing related.

Motion-related artefacts

The most common source of artefacts in DSA is motion between the mask and live images.
Even small positional shifts (as little as one pixel) can produce visible misregistration.

Type of motion	Cause	Appearance	Correction / Prevention
Patient movement	Voluntary movement, discomfort, coughing	Double edges or “ghost” anatomy	Patient immobilisation, short acquisition, breath-hold
Respiratory motion	Thoracic or abdominal movement	Periodic edge artefacts, misaligned diaphragm	Suspend respiration during acquisition
Cardiac motion	Pulsation of nearby vessels or mediastinum	Blurring or alternating subtraction edges	ECG gating (where available)
Table or equipment movement	Mechanical instability	Uniform shift of all structures	System stabilisation, pixel shift correction

Pixel shift correction

Small translational misalignments can be corrected by digitally shifting the mask image in x and y directions until optimal alignment is achieved.

Remasking

If movement or early contrast contaminates the mask, a new frame from the same series can be redefined as the mask to regenerate a cleaner subtraction.

Contrast-related artefacts

Artefact	Cause	Appearance / Effect	Prevention
Mask contamination	Contrast enters field before mask acquisition	Residual positive signal (vessel outline visible before injection)	Acquire new mask or use remasking
Incomplete opacification	Inadequate injection rate or catheter malposition	Patchy vessel filling or apparent stenosis	Adjust injector rate and catheter position
Reflux or turbulence	High injection pressure	Irregular enhancement or pseudo-lesions	Optimise injection rate and pressure
Overexposure (saturation)	Excessive contrast density or high mA	Clipped signal, bright vessel cores with dark halos	Reduce iodine concentration or exposure

Proper synchronisation of contrast delivery and exposure onset is critical for avoiding subtraction errors.

Detector and system artefacts

Even with optimal patient and contrast control, artefacts can arise from imperfections in the imaging chain.

Artefact	Physical cause	Appearance	Correction / QA action
Lag / ghosting	Residual charge in detector (especially a-Se systems)	Faint persistence of previous image	Calibration, short integration time
Veiling glare	Internal light scatter within intensifier or detector	Reduced contrast, diffuse haze	Flat-field correction and calibration
Fixed-pattern noise	Detector gain non-uniformity	Checkerboard or “fixed” texture	Gain map correction
Linearity error	Saturation or non-linear response	Residual bone or anatomy post-subtraction	Detector recalibration

Processing artefacts

Post-processing and image enhancement can introduce artefacts if over-applied or misused.

Artefact	Source	Impact	Avoidance
Excessive edge enhancement	Over-sharpening filters	Artificial vessel outlines or ringing artefacts	Moderate enhancement only
Over-filtering	Heavy temporal or spatial smoothing	Loss of fine vascular detail	Use adaptive filters tuned to flow rate
Improper pixel shift	Misaligned correction	Worsened artefacts or ghosting	Verify alignment before applying shift
Dynamic range compression	Display scaling	Flattened greyscale or contrast loss	Adjust gamma and window levels appropriately

Key takeaways and exam tips:

Motion is the most common cause of artefacts; corrected by pixel shift or remasking.
Mask contamination and contrast timing errors produce false-positive vascular signals.
Detector artefacts (lag, veiling glare, non-uniformity) degrade contrast; QA prevents recurrence.
Over-processing can create false vessel edges or blur fine detail.
DSA is inherently sensitive to motion, dose, and timing.
Common exam question: “List the common artefacts encountered in DSA, explain their causes, and outline how they can be minimised or corrected.”

Up next

Next, we’ll move on to Image Quality and Noise in DSA, which will examine the major determinants of image quality (including subtraction noise propagation, temporal resolution, and the trade-off between SNR and dose) with strategies for optimisation.