Neurosurgery notes/Radiology/MRI/Black-blood MR angiography (BBMRA)

Black-blood MR angiography (BBMRA)

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MRI

General

  • A dark-blood MR angiogram is not the same as simply inverting the Gray-scale image of a bright-blood MR angiogram. Completely different methods are responsible for the vascular contrast observed.

3 Technique

  • Utilizes a non-T1 contrast spin-echo type technique
  • Inversion Recovery (IR) Black Blood MRA
  • Susceptibility-Weighted (SW) Black Blood MRA

Mechanism

  • Signal from flowing blood is suppressed (rendering it "black") rather than enhanced as it is in conventional Bright Blood MRA techniques
    • Rapidly flowing or turbulent blood has a naturally low signal because of phase-dispersion and time-of-flight signal losses.
    • These effects may be further accentuated by application of flow-spoiling gradients, saturation bands, and/or inversion pulses.
    • The well-recognized vascular "flow voids" seen on routine MR imaging represent a crude form of dark-blood MRA.
  • In theory, dark-blood MRA has some unique advantages compared to bright-blood techniques.
    • Flow separation and turbulence, which cause unwanted signal losses and overestimation of stenoses on bright-blood MRA, paradoxically improve image quality on dark-blood MRA.
    • Because intraluminal signal is suppressed, vessels containing "black blood" do not generate pulsation (ghosting) artifacts.
    • Additionally, the lack of intraluminal signal allows the walls of vessels (or cardiac chambers) to be clearly delineated.

Aim

  • To look at vascular walls
    • Atherosclerotic plaque
    • Dissection
    • Check for SAH
      • Whether a vessel has bled
    • Check for Vasospasm

Disadvantage

  • Difficult in separating black blood from other low signal structures
    • Calcification
    • Bone
    • Air
  • Although an excellent method for imaging high-flow vessels, dark-blood techniques are less sensitive to slower flow states.
    • Vertebral artery dissection (arrow). Note dark blood “flow voids” in other arteries (but not the veins).
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  • To convert a set of dark-blood source images into an angiographic-style picture requires a minimum intensity projection method.
    • By comparison, bright-blood MRA is typically displayed using a maximum intensity projection algorithm.
    • The minimum intensity method required for dark-blood MRA requires considerable manual editing to exclude air (both inside and around the patient) as well as cortical bone and other low signal non-vascular structures.
      • As such, dark-blood MRA studies are usually displayed as tomographic sections rather than as angiogram-like projections.
  • Flow-spoiled black blood MRA is part of Canon’s V-TRACE sequence
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