Artifacts at Cardiac MRI

51 Pages·2013·8.69 MB·English

Artifacts at Cardiac MRI: causes and how to avoid them
Poster No.: 415
Congress: ESCR 2013
Type: Poster Presentation
Authors: A. Gyftopoulos, N. Kiriakopoulos, G. Delimpasis, S. KOROPOULI;
ATHENS/GR
Keywords: MR physics, Cardiac, MR, Diagnostic procedure, Quality
assurance, Artifacts
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Page 1 of 51
Purpose
• To review the artifacts of certain pulse sequences used at Cardiac MRI
• To explain the physics underlying the propagation of each artifact type
• To describe useful tips to avoid them
• To demonstrate the imaging chalenges at CMR and the apropriate solutions
• How to avoid potential diagnostic pitfalls
Methods and Materials
Examinations were performed on a 1.5-T MR unit (Siemens Sonata Maestro).
Images for this section:
Fig. 5
Page 2 of 51
Results
There are numerous kinds of artifacts that can occur in Cardiac MRI (motion-related
Fig. 31 on page 42 or ghosting artefacts , aliasing , turbulent flow, suspectibility
artefacts ,dark band artifacts (SSFP) Fig. 23 on page 41 ,dark rim and DHE artifacts
etch). Most of them are related to specific pulse sequences. Some effect the quality of
the MRI exam while others do not effect the diagnostic quality but may be confused with
pathology.
Nonetheless cardiac MRI is now entirely feasible thanks to the implemented techniques
such as ECG triggering, respiration gating, ultrafast or even real-time imaging methods
that have efficiently minimized or overcome cardiac and breathing motion artifacts
• In the heart the EPI technique is prone to artifacts.
Balanced SSFP sequences provide high-speed T2*/T1 contrast images. the high speed
allows rapid assessment of acute abdominal conditions in patients who are unstable or
unable to stay in the magnet a long time.
Good blood/myocardium contrast and high speed make balanced SSFP sequences
suitable for cardiac imaging applications.
Page 3 of 51
Fig. 6
References: RADIOLOGY, 251 HELLENIC AIR FORCE HOSPITAL - ATHENS/GR
Page 4 of 51
Fig. 7
References: RADIOLOGY, 251 HELLENIC AIR FORCE HOSPITAL - ATHENS/GR
Page 5 of 51
Fig. 8
References: RADIOLOGY, 251 HELLENIC AIR FORCE HOSPITAL - ATHENS/GR
Page 6 of 51
Fig. 9
References: RADIOLOGY, 251 HELLENIC AIR FORCE HOSPITAL - ATHENS/GR
Page 7 of 51
Fig. 10
References: RADIOLOGY, 251 HELLENIC AIR FORCE HOSPITAL - ATHENS/GR
Real time imaging is very helpfull in patient who can't hold their breath for a long time
Fig. 22 on page 40 .
Darkband artefact is not apparent in areas of low signal intensity.
Is is caused by dephasing of the spins with loss of steady -state (field inhomogeneity,off
-resonanse frequency) Fig. 2 on page 22 .
It is contributed by increased TR (inversely related to TR) ,low TE (increased chemical
shift artifact) and is worse at 3Tesla.
T2 IMAGING Fig. 29 on page 44 Fig. 30 on page 43
T2w-imaging is prone to several problems :
• variability in signal intensity caused by phased array coils,
Page 8 of 51
• improper timing causing signal loss in the posterior wall,
• high signal from slow flowing blood adjacent to the jeopardized myocardium
( can mimic and mask adjacent myocardial edema ),
• motion artifacts, and
• subjective nature of image interpretation of T2w sequences
Saturation bands are extremely usefull. We use three bands for SA images and one at
4CH.
A slight increase (10-20msec) in TI may help when there is signal loss in the lateral or
posterior wall.
T2-values for normal myocardium typically range between 50 and 55 ms on a 1.5T
scanner.
Fig. 11
References: RADIOLOGY, 251 HELLENIC AIR FORCE HOSPITAL - ATHENS/GR
Phase contrast
Page 9 of 51
Two opposites gradients are used , the first induces phase shift in flowing blood and
stationary tissue and the second reverses the phase shift of the latter.
Three images are obtained:
• Magnitude (used for anatoming contouring) Fig. 3 on page 23
• Re-phased magnitude (reconstructed image -flowing blood appears bright)
• Phase which is a substracted velocity image (grayscale value: White:
positive direction ,Black: negative direction , gray : Stationary spins) Fig. 1
on page 21
Fig. 12
References: RADIOLOGY, 251 HELLENIC AIR FORCE HOSPITAL - ATHENS/GR
Page 10 of 51