1. MR Angiography at 3T in the follow-up of coiled cerebral aneurysms:
ESNR-ESONR Exams 2010 Session
Fellowship in Neuroradiology
XIX Symposium Neuroradiologicum
Bologna, 6th October 2010
MR Angiography at 3T in the follow-up of coiled cerebral aneurysms:
to use Gadolinium or not?
Good morning to all listeners.
Paolo Vezzulli

2. 3D-TOF limitations: DSA 3D TOF CE-MRA
3D-TOF MRA at 3.0T yields images with a higher quality than that of 1.5 T TOF-MRA in terms of better spatial resolution and better delineation of vessel walls (Gibbs GF, AJNR 2004).
Intermodality agreement between 3D-TOF MRA at 3.0T and DSA is excellent (k=0.86 in Urbach H, Neuroradiology, 2008 and k=0.86 in Ferrè JC Eur Radiol, 2009).
The sensitivity of TOF-MRA compared with DSA for detection of residual aneurysms ranged from 71 to 97% and specificity from 89 to 100% (Ferré JC Eur Radiol, 2009)
3D-TOF limitations:
turbulent and slow residual flow in a coiled aneurysm may result in signal loss, because of intravoxel dephasing and spin saturation (particularly in large remnants) (Ozsarlak O, Neuroradiology 2004; Yamada, N, AJNR 2004; Atlas SW, 4th Ed 2008).
susceptibility artifacts due to coil packing : related to distortion of local B0 field and to eddy currents (Hartmann J, AJNR, 1997; Roy D, AJNR 1997; Weber B Eur Radiol, 2001). 3T could lead to greater coil-related artifacts (Majoie CB, AJNR 2005).
intra- or extra-luminal blood-clot interpreted as flow (Kahara VJ, AJNR 1999; Gauvrit, AJNR 2005)
TOF MRA at 3T yields higher spatial resolution and delineation of vessel walls than 1.5T. It has excellent intermodality agreement with DSA, with good sensitivity and specificity in remnants detection. However 3D-TOF acquisition suffers some limitations, the most relevant of which is its inherited low sensitivity to turbulent and slow flow, resulting in signal loss inside remnants, particularly in large ones.
DSA
3D TOF
CE-MRA

3. spin saturation effect can be eliminated by Gd-injection (T1-shortening effects of flowing blood from 1.2 sec down to ms) (Cottier JP, AJNR 2003; Atlas SW, 4th Ed 2008)
use of ultra-short TE in CE-MRA reduce signal loss related to transverse dephasing (Anzalone N, AJNR 2000; Anzalone N, Invest Radiol 2008; Atlas SW, 4th Ed 2008). The use of short TE (<2.5 msec) reduced artifacts (Gonner F, AJNR 2005; Walker MT, AJNR 2005).
CE-MRA
More precise detection of slow flow in CE-MRA may improve evaluation of residual patency in treated large and giant aneurysms and better definition of the distal branch arteries (AnzaloneN, AJNR 2000, Cottier JP, AJNR 2003, Pierot L, AJNR 2006)
To overcome this problems Gd-injection and ultra-short TE could be used in order to reduce spin saturation effect and transverse dephasing, obtaining CE-MRA, which is more sensitive to slow flow inside the coils, improving large and giant aneurysms remnants evaluation. CE-MRA has high sensitivity and specificity in remnants detection, at least equivalent to DSA, being particular useful to rule out “helmet remnants” and to assess early aneurysm recanalization.
CE-MRA is at least equivalent to DSA (Agid R, AJNR 2208; Gauvrit JY, Stroke 2006) for characterization of aneurysm remnants after coiling (sens. 86.8%; spec. 91.9% Kwee TC, Neuroradiology 2007): contrast filling within coils is more clearly seen with CE-MRA.
CE-MRA was preferred over DSA in 91% of the “helmet type” remnants (Agid R, AJNR 2008, Farb RI, Neuroradiology 2005) and seems to be highly sensitive to predict early aneurysm recanalization (Gauvrit JY, AJNR 2005)

4. CE-MRA AT 3.OT
Increased conspicuity of contrast enhancement should be associated with increased intravascular signal compared to background (Merkle EM, Acad Radiol 2007)
3D-TOF MRA and CE-MRA perform comparably at 3.0T for evaluation of intracranial aneurysms (Nael K, AJNR 2006; Wilkstrom J, Acta Radiol 2008; k=0.71 in Sprengers MES, AJNR 2009), The sensitivity
of TOF-MRA and CE-MRA is 75%, the specificity of TOF-MRA is 98% and of CE-MRA is 97%, with good correlation with DSA for both techniques (Sprengers MES, AJNR 2009)
Use of contrast material has no additional value in the evaluation of occlusion status… (Majoie CB, AJNR 2005)
…nor in the evaluation of parent or branch vessel patency
(Majoie CB, AJNR 2005)
3D-TOF
CE-MRA
3D-TOF
CE-MRA
Gadolinium injection should be associated, especially at 3T, with increase intravascular signal compared to background tissue. But, according to literature, enhanced and unenhanced MRA are rated as equal at 3T in the follow-up of treated aneurysms. Many of the published papers that deal with this issue stated that Gadolinium injection does not improve the detection of residual patency nor the definition of parent artery.
NPV for incomplete occlusion at 6-month follow-up are the same for TOF and CE-MRA; PPV of CE-MRA was somewhat lower than that of TOF
(Sprengers MES, AJNR 2009)

5. (Anzalone N, Invest Radiol 2008)
TOF-MRA follow-up of coiled aneurysms is better at 3T than at 1.5T; nevertheless, greater definition of residual patency is achieved with ultrafast CE-MRA at 1.5T
TOF-MRA at 3 T was preferred to TOF-MRA at 1.5 T in 37.9% of cases
CE-MRA at 1.5T was preferred to TOF-MRA at 3T in 10.3% of cases
“…we noted a benefit of CE-MRA at 1.5 T compared to 3D TOF-MRA at both 1.5 T and 3 T…”
(Anzalone N, Invest Radiol 2008)
However, in this recent paper, which came out in 2008, CE-MRA at 1.5T achieved greater definition of remnants over 3T TOF. As you can appreciate in the images at the bottom of the slide, a benefit from Gadolinium injection at 1.5 T was noted, in the evaluation of residual patency, even when images were compared to TOF at 3T.
CE-MRA 1.5T
3D-TOF 3T
3D-TOF 1.5T
DSA

6. To compare unenhanced 3DTOF MRA and CEMRA at 3T for the evaluation of coiled aneurysms
44 patients (14♀ e 30♂ - mean age 56y, range 38-74y)
46 aneurysms (40 small, 6 large);
mean interval between coiling and MRA: 25 months (1d-36m)
3T Philips Intera
In order to evaluate the role and supposed usefulness of Gadolinium in the follow-up of coiled intracranial aneurysms, we compared enhanced and unenhanced MRA at 3T. In this is a personal series, 44 Patients with 46 coiled aneurysms underwent, in the same session, 3D-TOF and CE-MRA on a 3T MR-scanner.
3D TOF MRA (10’) - TR 23, TE 3.5, FOV 250, SENSE factor 2.5, 180 slices, voxel size 0.5 x 0.5 x 1 mm
3D CEMRA (24”) - TR 5.9, TE 1.8, FOV 220, SENSE factor 3, 50 slices, voxel size 0.43 x 0.43 x 0.4 mm Gd-BOPTA 0.1mmol/kg + 25ml flush of the 0.9% saline injected at a 1.8ml/sec rate.
Source images, 3D reconstructions MIP and VR were evaluated

7. Patency (Roy-Raymond classification)
Coil Artifacts
3D TOF: 5 aneurysms
CEMRA: 0 aneurysms
Patency (Roy-Raymond classification)
Each acquisition was evaluated independently. We looked for coil-related artifacts, and patency, accordingly to the classification Roy Raymond classification in which treated aneurysms are classified as completely occluded or with residual neck (class 1) or as residual aneurysm (class 2). As you can see from we had only one mismatch.
These are the key cases
3D TOF 20 19 18 19 8
CEMRA

8. 3D TOF
CEMRA
This is a Patient with a ruptured aneurysm of the Anterior Communicating Artery treated with coils. If you look at the TOF study, and focus on the MIP, you will notice that the right anterior cerebral artery is partially hidden by coils artifact, while it is assessable after contrast injection. This case demonstrate that contrast injection could help in overcoming coil-related artifacts.
3D TOF

9. CEMRA DSA post DSA post 3D TOF CEMRA
This is the mismatch-case between 3D-TOF and CE-MRA, involving a partially thrombosed giant aneurysm of the right internal carotid bifurcation, treated with an internal-external carotid by-pass followed by coiling. 3D TOF MRA shows a significant signal drop at the level of the right MCA and no flux within omolateral A1, suggesting occlusion of the bypass. No residual aneurysm can be detected, maybe due to saturation effect or hidden by the paramagnetic artifact due to the thrombus. CEMRA depicts a small neck remnant and, furthermore, patency of the bypass can also be assessed.
3D TOF
CEMRA

10. 3D TOF CEMRA CEMRA 3D TOF CEMRA CEMRA
This is another case of an Anterior Communicating Artery ruptured aneurysm treated with coils. On source images you can see the presence of high signal spots within the coils. After the injection of Gd-BOPTA you can appreciate the presence of narrow stripes of contrast both at the neck and in the sac, confirming patency.
3D TOF
CEMRA
CEMRA

11. DSA pre DSA post DSA post CEMRA 3D TOF CEMRA CEMRA
This are DSA images of a patient with large sovraofthalmic carotid artery aneurysm, partially trombosed and treated with GDC. Even in this case patency is better assessed by CEMRA.
3D TOF
CEMRA
CEMRA

12. DSA post 3D TOF CE MRA DSA post 3D TOF CEMRA CEMRA DSA post
The last case I would like to show you is this Patient with a giant basilar tip aneurysm, who underwent endovascular treatment after rupture. Patency was detected at DSA performed 8 months after endovascular procedure. 3D-TOF showed the presence of blood flow inside the aneurysmatic sac. Source images and 3D-reconstruction of the CEMRA acquisition aid in the understanding of the architectural features and the entity of the patency, as well as the relationship between the aneurysmatic sac and the posterior cerebral arteries.
DSA post

13. Our data confirm that follow-up with
CEMRA of coiled aneurysms at 3T is feasible.
CEMRA demonstrated the presence of residual patency at neck
not evident at TOF MRA in 1 case.
Moreover it demonstrated to be less sensitive to the presence of artifacts and better showed the residual patency (30.7% of cases; p=0.001)
In conclusion CEMRA at 3T is feasible. CEMRA is less sensitive than TOF to coil-related artifacts and it better shows patency, being able to show a small neck remnant not detected by TOF MRA in 1 case. Our results confirm what Wallace reported in his nice review, published in 2007, in which he stated that even if TOF MRA and CE-MRA closely correlates, in several cases CE-MRA could aid in the visualization of small remnants and moreover could uncover a larger neck remnant that were not anticipated on TOF acquisition. However, since the real advantage of CEMRA over TOF is in the demonstration of small type 1 remnants, it is important to underline that we do not know how many of them will grow to become treatable and how long this process will take; so actually, from a clinical point of view, we do not know how relevant is the advantage of CE-MRA over TOF.
“…the real advantage of CE-MRA over TOF acquisitions is in the demonstration of small type 1 remnants; however, such remnants are not considered treatable by most interventionists. We do not yet know how many of these residual aneurysms will grow to become treatable, and consequently, we do not really know how relevant the advantage of CE-MRA actually is from a clinical perspective…”
“…3D TOF MRA without contrast is generally accurate and closely correlates with the findings of contrast-enhanced techniques…” but “…in several cases contrast enhancement aided the visualization of small remnants and uncovered a larger neck remnant or filling of the coil pack that was not anticipated on the noncontrast MRA technique…”

14. Blood-Pool Contrast Medium (BPCM)
7T-9T
FUTURE PERSPECTIVES
Blood-Pool Contrast Medium (BPCM)
Time-Resolved 3D-MRA (3D-TRICKS/TREAT) ?
Von Morze C, J Magn Reson Imag, 2007
BPCM, due to prolonged blood-retention time resulting in increased relaxivity, overcomes false neck remnant in CE-MRA (GD-enhancement of the organized thrombus) and shows sharper definition of parent vessel. (Kau T, AJNR 2009).
BPCE-MRA shows higher sensitivity (91.7% vs. 87.5%) and higher specificity (92.3% vs. 76.9%) compared with TOF-MRA (Kau T, AJNR 2009).
In the next future higher-field strength scanner and Blood-Pool Contrast media could further improve CEMRA image quality and accuracy.
Drawback: venous contaminations in steady-state acquisitions (FP)

15. Thank you