1. Comparison of MRA Techniques for Calcification Detection
M. Mossa-Basha1, H. Liu1, D. Hippe1, N. Balu1, J. Sun1, D. Shibata1, C. Yuan1
1Department of Radiology, University of Washington

2. Disclosures
None relevant to this presentation

3. Background Intracranial vascular calcifications Associated with
Current and future stroke1,2
Cognitive decline and dementia 3,4
Microstructural changes on DTI and increased volume of white matter disease4

4. Background Intracranial vascular calcification detection
Thin-slice CT is the reference standard
Development of MRI techniques for detection important to avoid radiation and with CTA, potentiation of radiation-related mutations from iodinated contrast CT
CTA

5. Background 3D TOF MRA has been employed for calcification detection CT

6. Background
Simulataneous Non-Contrast Angiography and intraPlaque Hemorrhage (SNAP)5
Slab selective phase sensitive inversion recovery sequence
Produces heavily T1-weighted dark blood (plaque hemorrhage) and bright blood (MRA) images

7. SNAP: Plaque Hemorrhage
Background- SNAP
Slab selective phase-sensitive inversion recovery sequence
Negative signals creates MRA
Positive signals produces iph
SNAP: MRA
SNAP: Plaque Hemorrhage
SNAP: Joint

8. Dual SNAP Contrast using Phase Sensitive Polarity Maps
Balu N et al, ISMRM 2014, Milan
SNAP1
IPH
Angiogram (Stenosis)
SNAP2
Calcification
Plaque burden
SNAP1 I1 I2
SNAP2
Phase Sensitive Polarity Map

9. Dual contrast with phase sensitive maps:
S1 shows phase corrected T1w image. This is the traditional SNAP image but does not show calcification or outer wall boundaries.
S1<0 provides MRA of SNAP for luminal surface evaluation.
I2 shows juxtaluminal calcification
S2 is generated from I2 using the phase sensitive polarity function map generated from S1 or the original SNAP and reference images. S2 provides a PD weighted black- blood image to show plaque boundaries (lumen and outerwall).
High risk plaque identification using four weightings from a single scan. Red arrow: Intraplaque hemorrhage, yellow arrows: Calcification

10. Purpose
To evaluate the ability of SNAP Ref to detect intracranial artery wall calcifications as compared 3D TOF MRA relative to thin slice CT/CTA.

11. Methods
After IRB approval, radiology database was reviewed for consecutive patients who underwent a clinical MRA exam
Requirements
3D TOF MRA and SNAP imaging performed
Scanned on a 3T Philips Ingenia (Philips Healthcare; Best, Netherlands) MR scanner
Thin-slice (0.625 mm) CT or CTA examination within 1 year of the MRA exam

12. MRI Parameters TOF MRA SNAP TR/TE (ms) 23/3.45 13/7.3
TOF MRA
SNAP
TR/TE (ms)
23/3.45
13/7.3
In-plane resolution (mm)
0.4 x 0.6
0.6 x 0.6
Slice thickness (mm)
0.6
Flip angle 18 15
FOV (mm)
200 x 200 x 126
180 x 180 x 45
Matrix
500 x 332
300 x 300
NSA 1
SENSE (RL/FH)
2.5/1 -
Slices
210
150
Oversample factor
1.25
Scan time
7:45
9:38

13. Image Analysis
A blinded review was performed by a board certified neuroradiologist
Consecutive SNAP2 sequences reviewed in random order, followed by 3D TOF MRA and finally thin slice CTA images in consecutive days, all images reviewed in axial plane
Intracranial arterial segments evaluated individually:
cavernous, ophthalmic, supraclinoid and terminal carotid artery segments, M1 middle cerebral, A1 anterior cerebral, P1 posterior cerebral arterial segments on the right and left and the basilar artery

14. Statistical Methods
Sensitivity and specificity for detecting calcification per vessel was computed for SNAP2 and TOF-MRA using CT as the reference standard.
Overall agreement with CT was assessed using unweighted Cohen’s kappa and linearly weighted Cohen’s kappa for both SNAP2 and TOF-MRA.

15. Statistical Methods
Agreement was assessed for presence/absence of calcification per vessel and calcification size category per vessel (none, <50% circumferential involvement and >50% circumferential involvement) based on previously established evaluation.
Diagnostic performance and agreement metrics were compared between SNAP2 and TOF-MRA using the non-parametric bootstrap, to account for potential dependence between vessels from the same subject.

16. Results 11 patients included 143 total arterial segments
129 segments were analyzable on all modalities
7 of the 11 patients had calcification identified in at least 1 arterial segment

17. Results Modality Arteries Segment No. SNAP N(%) TOF-MRA N(%) CT N(%)
Modality
Arteries
Segment
No.
SNAP N(%)
TOF-MRA N(%)
CT N(%)
All arteries
Any segment
129
29 (22.5)
17 (13.2)
24 (18.6)
Internal carotid artery 79
27 (34.2)
13 (16.5)
24 (30.4)
Cavernous 18
5 (27.8)
3 (16.7)
6 (33.3)
Supraclinoid 21
14 (66.7)
4 (19.0)
13 (61.9)
Ophthalmic
1 (5.6)
Terminus 22
3 (13.6)
5 (22.7)
0 (0.0)
Anterior arteries 44
1 (2.3) A1 M1
1 (4.5)
Posterior arteries
Basilar artery 6
2 (33.3)
3 (50.0)

18. Results Using CT as reference standard
SNAP had higher sensitivity (75.0% vs. 29.2%, p=0.01) and similar specificity (89.5% vs. 90.5%, p=0.8) compared to TOF-MRA
SNAP: higher agreement with CT for calcification compared to TOF MRA
Presence/absence (kappa: 0.60 vs. 0.22, p=0.01)
Calcification size categories (weighted kappa: 0.61 vs. 0.20, p=0.008)

19. Diagnostic performance of SNAP and TOF-MRA and agreement with CT
SNAP
TOF-MRA
Difference (SNAP - TOF)
Metric
Estimate
(95% CI)
P-value
Sensitivity, %
75.0%
( %)
29.2%
( %)
45.8%
( %)
0.014
Specificity, %
89.5%
( %)
90.5%
( %)
-1.0%
( %)
0.79
Unweighted kappa (presence/absence)
0.60
( )
0.22
( )
0.38
( )
0.012
Unweighted kappa (size)*
0.51
( )
0.11
( )
0.40
( )
0.003
Weighted kappa (size)*
0.61
( )
0.20
( )
0.41
( )
0.008

20. Comparison of Calcification on CT, SNAP I2 and TOF MRA
Non-contrast CT
SNAP I2
TOF MRA
Calcifications (short arrows) are shown on CT, SNAP I2 and TOF MRA. Due to improved contrast resolution between calcifications and background tissues, on SNAP I2 calcifications are more readily appreciated relative to TOF MRA.

21. Discussion/Conclusion
This study shows the feasibility of SNAP I2 for the evaluation of intracranial calcifications.
In comparison to 3D TOF MRA, SNAP I2 more accurately depicted calcifications.
When combined with the MRA and intraplaque hemorrhage images provided by SNAP, this technique can provide first line luminal and vessel wall imaging information with a single acquisition.

22. References
1. Bos D, Portegies ML, van der Lugt A, et al. Intracranial carotid artery atherosclerosis and the risk of stroke in whites: the Rotterdam Study. JAMA neurology 2014;71(4): Bos D, van der Rijk MJ, Geeraedts TE, et al. Intracranial carotid artery atherosclerosis: prevalence and risk factors in the general population. Stroke; a journal of cerebral circulation 2012;43(7): Bos D, Vernooij MW, de Bruijn RF, et al. Atherosclerotic calcification is related to a higher risk of dementia and cognitive decline. Alzheimer's & dementia : the journal of the Alzheimer's Association 2015;11(6): e1. 4. Bos D, Vernooij MW, Elias-Smale SE, et al. Atherosclerotic calcification relates to cognitive function and to brain changes on magnetic resonance imaging. Alzheimer's & dementia : the journal of the Alzheimer's Association 2012;8(5 Suppl):S Wang J, Bornert P, Zhao H, et al. Simultaneous noncontrast angiography and intraplaque hemorrhage (SNAP) imaging for carotid atherosclerotic disease evaluation. Magnetic resonance in medicine 2013;69(2): Koton S, Tashlykov V, Schwammenthal Y, et al. Cerebral artery calcification in patients with acute cerebrovascular diseases: determinants and long-term clinical outcome. European journal of neurology : the official journal of the European Federation of Neurological Societies 2012;19(5):