Briefly describes the procedure of Digital Subtraction Angiography, and its applications in the field of Interventional Radiology

1. Vascular Interventions : Clinical Applications
Dr. ANMOL RATTAN SINGH UBEROI , MBBS
DNB RADIODIAGNOSIS TRAINEE
BLK SUPER SPECIALITY HOSPITAL
NEW DELHI

2. Definition
• Angiography ?
ANGIO means blood vessel
And angiography is the radiological study of blood
vessels in the body after the introduction of iodinated
contrast media.
• Subtraction ?
It is simply a technique by which bone structure images
are subtracted or canceled out from a film of bones plus
opacified vessels, leaving an unobscured image of the
vessels.

3. The acquisition of digital fluoroscopic images combined
with the injection of contrast material and real-time
subtraction of pre and post contrast images to perform
angiography is referred to as digital subtraction
angiography .

4. Historical Development
• In 1927, the Portuguese neurologist Egas Moniz, (Nobel Prize
winner 1949), developed the technique of contrast x-ray
cerebral angiography to diagnose diseases, such as tumors
and arteriovenousmalformations.
• The idea of subtraction image was first proposed by the
Dutch radiologist Ziedses des Plantes in 1935, when he was
able to produce subtracted images using plain films, using
simplephotographicmethodtoeliminateunwantedimages.

5. 5
Digital Subtraction Angiography (DSA)
DSA refers to a technique which compares two images of a
region of the body, before and after a contrast medium has
been injected into the body, for the purpose of studying
blood vessels.

6. 6
Digital Subtraction Angiography (DSA)
• DSA uses an Image
Intensifier/ Television
system combined with a
high speed image
processor in a digital
angiographic
system.

7. Principles Of Subtraction
The principles of subtraction are based on the
following:
• The scout film shows the structural details of the
skull and the adjacent soft tissue.
• Angiogram film shows exactly the same anatomic
details, plus the opacified blood vessels.
• If all the information in the scout film could be
subtracted from the angiogram film, only the
opacified vessel pattern would remain visible.

8. 8
Subtraction
Pre-contrast image Post-contrast image Subtracted image

9. Basis Of Contrast
Blood vessels are not normally seen in an x-ray image, because of low
tissue contrast.
To increase image contrast, contrast agents, which are dense fluids
with elements of high atomic numbers, such as iodine, are injected
into a blood vessel during angiography.
Because of its higher density and high atomic number, iodine absorbs
photons more than blood and tissue.
This creates detailed images of the blood vessels in real time.

10. Mask subtraction
Dual energy subtraction
Time interval differencing
Temporal filtering
3-D Road Mapping
XperCT
3-D Reconstruction
Edge Enhancement
Techniques & Advancements

11. Mask Subtraction
•The image before the contrast agent is administered is called
the mask image.
•Once the contrast is administered, a sequence of images are
taken by a television camera in analog form, which is then
digitised by the computer.
•The DSA processor has two separate image memories, one for
the mask and the other for the images with contrast medium.
•These two image memories are subtracted from one another
arithmetically, and the result goes to an image processing and
display unit.

12. The mask image is
subtracted from the
image with dye to
reveal just the
vessels
uncontaminated by
the overlying bone
structures.
PRE CONTRAST POST CONTRAST
SUBTRACTED ENHANCED

13. 13
Mask Image

14. Dual Energy Subtraction
Two images are taken within a very short period
(no patient movement)
One image is taken at low KVp & the other at high
KVp.
K EDGE HYBRID

15. K edge Subtraction
Iodine attenuates diagnostic x-rays almost entirely.
One method for achieving high iodine contrast is
removal of all x-rays from the beam except those that
lie below the lowest energy shell of Iodine atom.
An x-ray filter made of rare earth named Cerium does
this well.
The image to be subtracted, hence contains few x-rays.

16. Hybrid Subtraction
Mask subtraction + Dual Energy subtraction
High KVp & low KVp image pair is collected.
Consider the subtracted images to consist of only 2
atomic no. materials (iodine & bone).
The hybrid subtraction produces 2 sets of subtracted
images.
The same bone & iodine structures are present on both

17. Time Interval Differencing
In simple mask subtraction, an early image is used as a
mask.
In this technique, a new mask is processed for each
subtraction.
Each subtracted image is the difference between the
images separated by some fixed interval of time.

18. Temporal Filtering
Temporal filters are used in this technique.
This filter generates one final image by adding and
subtracting some of the original images together, and
then shifting & repeating to form the next image.

19. Use of Road Mapping with clinical Images
• .

20. XperCT
With XperCT, clinicians can access CT-like imaging right on the angio system
so that they can assess soft tissue, bone structure and other body
structures before, during or after an interventional procedure.
This reconstruction can be overlaid with the 3D vascular image.
It brings 3-D soft tissue imaging to your angio suite.
3-D soft tissue imaging supports diagnosis, planning, interventions and
treatment follow-up.
Using CT-like imaging for a post-procedural check can help reduce delays
and improve patient comfort.

21. XperCT
XperCT overlay on both the internal carotid and vertebral arteries

22. 3-D Reconstruction

23. 23
Digital Advantage - Edge Enhancement
Original Image Blurred Image
Subtracted Image Edge-Enhanced image
(Edge-enhanced image = [original image - blurred version] + original image)

24. 24
Digital Subtraction Angiography (DSA)
Performed for diagnostic and therapeutic
purposes of vessel visualization in the body.

25. Indications
• Non Traumatic Subarachnoid Hemorrhage (SAH)
• Arterial dissection or laceration
• Aneurysm
• Pseudoaneurysm
• Thrombosis
• Arterio-venous malformation (AVM)
• Arterio-venous fistula (AVF)
• Tumor vascularity
• Gastrointestinal bleed / Uterine artery bleed
• Therapeutic

26. Contraindications
No absolute contraindication
Poor renal reserve
Deranged coagulogram
Allergy to contrast media
Recent contrast based examination

27. Diagnostic Value
• Cerebral - 4 vessel
• Upper & lower limb
• Renal
• IVC graphy
• Pulmonary
• Abdominal - coeliac & branches, SMA, IMA
• Transjugular liver biopsy
• Balloon occlusion test

28. Therapeutic Value
• Embolization
- coil
- gel
- particle
- balloon
• Stenting
• TACE
• Vertebroplasty

29. DIAGNOSTIC
USAGE

30. ACOM Aneurysm

31. ACA Aneurysm

32. MCA Aneurysm

33. PCOM Aneurysm

34. Basilar tip Aneurysm

35. ICA Aneurysm

36. Arterio-venous Malformation

37. Arterio-venous Fistula

38. Tumour vascularity

39. Coiling of cerebral aneurysms

40. THERAPEUTIC
USAGE

41. 41
Embolization

42. Lead pipe embolization

43. Gel embolization

44. Particle embolization
Uterus myoma – post embolization

45. Onyx embolization
 Onyx HD500 is comprised of 20% EVOH
(ethylene vinyl alcohol) copolymer
dissolved in DMSO (dimethyl sulfoxide),
and suspended micronized tantalum
powder to provide contrast for
visualization under fluoroscopy.
 Onyx HD500 (20% EVOH) is used for the
treatment of intracranial, saccular &
sidewall aneurysms that present with a
wide neck (≥ 4mm) or with a dome-to-
neck ratio < 2 that are not amenable to
treatment with surgical clipping.
 Onyx HD500 can also be used in
adjunctive therapy with Axium coils and
stents.

46. Stenting of ICA stenosis

47. Thrombolysis

48. Thrombectomy

49. TACE
A 78-year-old man with HCCs treated with TACE using DSA alone. A) CT showed two tumors in
the right lobe of the liver. B) Right hepatic arteriogram showed two tumor stains (arrows).
C) Selective arteriogram of the anterior superior subsegmental artery of the right hepatic artery
showed a tumor stain. Arrow indicates the TACE point. D) Selective arteriogram of the paracaval
branch of the caudate artery of the liver also showed a tumor stain. TACE was performed at this

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