Question of the day: What is T2*axial susceptibility weighted angiography (SWAN)?

Question:

What is T2*axial susceptibility weighted angiography (SWAN)?

	1. A gradient echo sequence.
	2. An MRI sequence acquired with varied TEs within a single TR period.
	3. An MRI sequence sensitive for paramagnetic substances that include blood products and calcifications.
	4. 3D volumetric thin sections are acquired.
	5. Is a modified conventional T1 weighted sequence.

Answer:

The correct answers for the question "What is T2*axial susceptibility weighted angiography (SWAN)?" are:

1. A gradient echo sequence.

2. An MRI sequence acquired with varied TEs within a single TR period.

3. An MRI sequence sensitive for paramagnetic substances that include blood products and calcifications.

4. 3D volumetric thin sections are acquired.

Explanation
SWAN is a gradient echo T2*-based multi-echo sequence. SWAN is acquired with varied TE times within one TR time period. SWI has a fixed TE and TR and is acquired using magnitude and phase components. Increased susceptibility signal and signal-to-noise ratio is achieved with SWAN and SWI sequences. Both SWI and SWAN are more sensitive for paramagnetic substances than conventional T2* GRE sequences. [T2* weighted susceptibility angiography ( SWAN, Optima 450, General Electric, Milwaukee, WI, USA) is a unique 3D-gradient echo T2*-based multi-echo sequence with varied TE times within one TR time period that allows for imaging of tissues with varying degrees of T2* contrast and is technically distinct from conventional 2D T2*GRE and SWI. A combined weighted average of all the echoes is collated by a specialized post-processing algorithm to obtain whole brain sub-millimeter-resolution 3D images [6]. The varied TE times reduces chemical shift artifact that contributes to image blurring on conventional 2D T2* GRE sequences. This also increases susceptibility signal and doubles the signal-to-noise ratio as compared to conventional 2D T2* GRE sequences].

From the manuscript:
Pediatric Holohemispheric Developmental Venous Anomaly: Definitive characterization by 3D Susceptibility Weighted Magnetic Resonance Angiography
Radiology Case. 2011 May; 5(5):10-18

This article belongs to the Neuro section.

From the manuscript

Pediatric Holohemispheric Developmental Venous Anomaly: Definitive characterization by 3D Susceptibility Weighted Magnetic Resonance Angiography

Free full text article: Pediatric Holohemispheric Developmental Venous Anomaly: Definitive characterization by 3D Susceptibility Weighted Magnetic Resonance Angiography

Abstract
We present a case of an incidentally discovered holohemispheric developmental venous anomaly (DVA) in a 12 year old, conclusively characterized by 3D T2* multi-echo sequence susceptibility weighted angiographic imaging (SWAN). For the evaluation of head trauma, abnormal right intraparenchymal and periventricular vascularity was identified by a non contrast head CT scan. Conventional MRI sequences revealed prominent veins with findings suspicious of a DVA. A definitive diagnosis was made by identifying angiographic features typical for DVA by augmented susceptibility weighted angiographic imaging. Using this sequence the entire hemispheric extent of the anomaly without complicating features was definitively characterized, negating the need for a catheter based angiographic study. A holohemispheric DVA in a child to our knowledge has not been previously described.

References

1. San Millán Ruíz D, Yilmaz H, and Gailloud P. Cerebral Developmental Venous Anomalies: Current Concepts. Ann Neurol 2009; 66(3): 271-283