Gamma knife surgery for arteriovenous malformations in the brain: integration of time-resolved contrast-enhanced magnetic resonance angiography into dosimetry planning

Planning of gamma knife radiosurgery (GKR) for brain arteriovenous malformations using triple magnetic resonance angiography (triple-MRA)

PURPOSE

Intra-arterial Digital Subtraction Angiography (DSA) is the gold standard technique for radiosurgery target delineation in brain Arterio-Venous Malformations (AVMs). This study aims to evaluate whether a combination of three Magnetic Resonance Angiography sequences (triple-MRA) could be used for delineation of brain AVMs for Gamma Knife Radiosurgery (GKR).

METHODS

Fifteen patients undergoing DSA for GKR targeting of brain AVMs also underwent triple-MRA: 4D Arterial Spin Labelling based angiography (ASL-MRA), Contrast-Enhanced Time-Resolved MRA (CE-MRA) and High Definition post-contrast Time-Of-Flight angiography (HD-TOF). The arterial phase of the AVM nidus was delineated on triple-MRA by an interventional neuroradiologist and a consultant neurosurgeon (triple-MRA volume). Triple-MRA volumes were compared to AVM targets delineated by the clinical team for delivery of GKR using the current planning paradigm, i.e., stereotactic DSA and volumetric MRI (DSA volume). Difference in size, degree of inclusion (DI) and concordance index (CcI) between DSA and triple-MRA volumes are reported.

RESULTS

AVM target volumes delineated on triple-MRA were on average 9.8% smaller than DSA volumes (95%CI:5.6-13.9%; SD:7.14%; p = .003). DI of DSA volume in triple-MRA volume was on average 73.5% (95%CI:71.2-76; range: 65-80%). The mean percentage of triple-MRA volume not included on DSA volume was 18% (95%CI:14.7-21.3; range: 7-30%).

CONCLUSION

The technical feasibility of using triple-MRA for visualisation and delineation of brain AVMs for GKR planning has been demonstrated. Tighter and more precise delineation of AVM target volumes could be achieved by using triple-MRA for radiosurgery targeting. However, further research is required to ascertain the impact this may have in obliteration rates and side effects.

Intracranial arteriovenous malformations

The treatment of arteriovenous malformations (AVMs) has evolved over the last 10 years. It is now possible to see that obliteration continues for up to 10 years and that the final obliteration rate may be between 85% and 90%. Improved imaging has made the treatment more efficient and has reduced the complications. It is possible to treat larger AVMs in a single session than was previously thought possible without increases in the complication rates. In addition, treatments of larger lesions can be staged. The use of 3D rotating angiography produces remarkable images which can be imported into GammaPlan. On the other hand efforts are ongoing to avoid the need for digital subtraction angiography, which would make the treatment a lot more comfortable.

Volumetric analysis of intracranial arteriovenous malformations contoured for CyberKnife radiosurgery with 3-dimensional rotational angiography vs computed tomography/magnetic resonance imaging

BACKGROUND

Accurate target delineation has significant impact on brain arteriovenous malformation (AVM) obliteration, treatment success, and potential complications of stereotactic radiosurgery.

OBJECTIVE

We compare the nidal contouring of AVMs using fused images of contrasted computed tomography (CT) and magnetic resonance imaging (MRI) with matched images of 3-dimensional (3-D) cerebral angiography for CyberKnife radiosurgery (CKRS) treatment planning.

METHODS

Between May 2009 and April 2012, 3-D cerebral angiography was integrated into CKRS target planning for 30 consecutive patients. The AVM nidal target volumes were delineated using fused CT and MRI scans vs fused CT, MRI, and 3-D cerebral angiography for each patient.

RESULTS

The mean volume of the AVM nidus contoured with the addition of 3-D cerebral angiography to the CT/MRI fusion (9.09 cm(3), 95% confidence interval: 5.39 cm(3)-12.8 cm(3)) was statistically smaller than the mean volume contoured with CT/MRI fused scans alone (14.1 cm(3), 95% confidence interval: 9.16 cm(3)-19.1 cm(3)), with a mean volume difference of δ = 5.01 cm(3) (P = .001). Diffuse AVM nidus was associated with larger mean volume differences compared with a compact nidus (δ = 6.51 vs 2.11 cm(3), P = .02). The mean volume difference was not statistically associated with the patient's sex (male δ = 5.61, female δ = 5.06, P = .84), previous hemorrhage status (yes δ = 5.69, no δ = 5.23, P = .86), or previous embolization status (yes δ = 6.80, no δ = 5.95, P = .11).

CONCLUSION

For brain AVMs treated with CKRS, the addition of 3-D cerebral angiography to CT/MRI fusions for diagnostic accuracy results in a statistically significant reduction in contoured nidal volume compared with standard CT/MRI fusion-based contouring.

Analysis of the influence of 4D MR angiography temporal resolution on time-to-peak estimation error for different cerebral vessel structures

BACKGROUND AND PURPOSE

Time-resolved MRA imaging is a promising technique for blood flow evaluation in case of cerebrovascular malformations. Unfortunately, 4D MRA imaging is a trade-off between spatial and temporal resolution. The aim of this study was to investigate the influence of temporal resolution on the error associated with TTP estimation from indicator dilution curves derived from different vascular structures.

MATERIALS AND METHODS

Monte Carlo simulation was performed to compute indicator dilution curves with known criterion standard TTP at temporal resolutions between 0.1 and 5 seconds. TTPs were estimated directly and by using 4 hemodynamic models for each curve and were compared with criterion standard TTP. Furthermore, clinical evaluation was performed by using 226 indicator dilution curves from different vessel structures obtained from clinical datasets. The temporal resolution was artificially decreased, and TTPs were estimated and compared with those obtained at the original temporal resolutions. The results of the clinical evaluations were further stratified for different vessel structures.

RESULTS

The results of both evaluations show that the TTP estimation error increases exponentially when one lowers the temporal resolution. TTP estimation by using hemodynamic model curves leads to lower estimation errors compared with direct estimation. A temporal resolution of 1.5 seconds for arteries and 2.5 seconds for venous and arteriovenous malformation vessel structures appears to be reasonable to achieve TTP estimations adequate for clinical application.

CONCLUSIONS

Different vessel structures require different temporal resolutions to enable comparable TTP estimation errors, which should be considered for achieving a case-optimal temporal and spatial resolution.

4D time-resolved magnetic resonance angiography for noninvasive assessment of pulmonary arteriovenous malformations patency

PURPOSE

To assess the capability of four-dimensional (4D) time-resolved magnetic resonance angiography (MRA) to assess pulmonary arteriovenous malformations (PAVMs) patency by analyzing pulmonary arterial and venous enhancement kinetics.

MATERIALS AND METHODS

Seven patients with eight documented patent PAVMs underwent a 4D-MRA with keyhole and viewsharing compression at 3T with the following parameters: spatial resolution 0.87 × 0.87 × 1.4 mm(3); field of view 500 × 350 × 238 mm(3); dynamic scan time (temporal resolution) 1.2 seconds; total acquisition time 18.1 seconds for six dynamic datasets (6 × 1.2 sec + reference scan: 10.9 sec). All images were reviewed by two experienced radiologists. Image quality was rated on a qualitative 5-point scale (1: not assessable to 5: excellent). Signal value was measured on cross-sectional planes for the afferent arteries and efferent veins of the PAVM, and for normal reference healthy arteries and veins. The difference in time to peak for each coupled artery/vein (dTTPav) was calculated and compared with a Mann-Whitney test between PAVMs and reference vessels.

RESULTS

Mean image quality was 3.2 ± 0.9. dTTPav was significantly smaller in PAVMs (0.15 ± 0.76 sec) than in reference vessels (3.75 ± 1.62 sec), P < 0.001.

CONCLUSION

4D-MRA is a promising tool for noninvasive assessment of PAVM patency.

Improved vessel delineation in keyhole time-resolved contrast-enhanced MR angiography using a gadolinium doped flush

PURPOSE

To prospectively assess the influence of a gadolinium doped saline flush compared with a pure saline flush on the image quality of the supra-aortic vessels using time-resolved contrast-enhanced MR angiography (4D CE-MRA) in a randomized double blind clinical trial.

MATERIALS AND METHODS

Twenty-two patients scheduled for contrast-enhanced craniocerebral MRI underwent a supplemental 4D CE-MRA covering the carotids to the superior sinus consisting of 30 dynamics of a T1-weighted 3D gradient-echo sequence (FFE) in sagittal direction. The temporal resolution of 1.1 s per dataset was achieved using the keyhole technique with the reference scan acquired at the end. Immediately after the intravenous (IV) injection of 0.1 mmol Gd/kg body weight of gadoterate, our patients received a 50-mL flush consisting either of a 0.9% saline solution (n = 11) or doped with 50 mM gadolinium (n = 11; total Gd: 0.11 mmol/kg) at a flow-rate of 2 mL/s. Vessel delineation, image quality, signal-to-noise- (SNR) and contrast-to-noise (CNR) ratios over time were compared.

RESULTS

Both vessel delineation (internal carotid artery [ICA]: slope(saline) = 308.5; slope(Gd) = 528.9; P = 0.006; superior sagittal sinus [SSS]: slope(saline) = 505.3; slope(Gd) = 674.9; P = 0.007) and CNR (ICA: CNR(saline) = 57.3; CNR(Gd) = 80.55; P = 0.0417; SSS: CNR(saline) = 74.15; CNR(Gd) = 117.4; P = 0.0331) of the ICA and SSS were significantly increased using the gadolinium doped flush.

CONCLUSION

A low concentrated gadolinium flush in comparison to a pure saline flush improves significantly vessel contrast and their delineation in time-resolved CE-MRA using the keyhole technique.

A virtual frame system for stereotactic radiosurgery planning

PURPOSE

We describe a computerized (or virtual) model of a stereotactic head frame to enable planning prior to the day of radiosurgery. The location of the virtual frame acts as a guide to frame placement on the day of the procedure.

METHODS AND MATERIALS

The software consists of a triangular mesh representation of the essential frame hardware that can be overlaid with any MR scan of the patient and manipulated in three dimensions. The software calculates regions of the head that will actually be accessible for treatment, subject to the geometric constraints of the Leksell Gamma Knife hardware. DICOM-compliant MR images with virtual fiducial markers overlaid onto the image can then be generated for recognition by the treatment planning system.

RESULTS

Retrospective evaluation of the software on 24 previously treated patients shows a mean deviation of the position of the virtual frame from the actual frame position of 1.6 +/- 1.3 mm. Initial clinical use on five patients indicates an average discrepancy of the virtual frame location and the actual frame location of <1 mm. MR images with virtual fiducial markers can be imported into radiosurgical treatment planning software and used to generate an initial treatment plan.

CONCLUSIONS

The virtual frame provides a tool for prospective determination of lesion accessibility, optimization of the frame placement, and treatment planning before the day of the procedure. This promises to shorten overall treatment times, improve patient comfort, and reduce the need for repeat treatments due to suboptimally placed frames.

Intracranial arteriovenous malformation: time-resolved contrast-enhanced MR angiography with combination of parallel imaging, keyhole acquisition, and k-space sampling techniques at 1.5 T

PURPOSE

To prospectively compare the agreement between digital subtraction angiography (DSA) and time-resolved magnetic resonance (MR) angiography with sensitivity encoding (SENSE) in combination with keyhole acquisition and contrast material-enhanced robust-timing angiography (CENTRA) k-space sampling techniques for the characterization of intracranial arteriovenous malformations (AVMs).

MATERIALS AND METHODS

The institutional review board approved the study; informed consent was obtained from all patients (or their parents). Twenty-eight patients (15 male, 13 female; mean age, 38.6 years; age range, 16-61 years) with 29 previously diagnosed, untreated intracranial AVMs who were referred for stereotactic gamma knife radiosurgery were evaluated. Preinterventional imaging included intraarterial DSA and time-resolved MR angiography. The time-resolved MR angiography sequence included SENSE with a 1.5-T imager and was optimized by applying keyhole acquisition and CENTRA techniques. Time-resolved MR angiograms were reviewed by two independent raters and compared with DSA images with regard to arterial feeders, nidus size, and venous drainage. kappa Statistics were applied to determine interobserver and intermodality agreement.

RESULTS

MR angiography enabled time-resolved (1.7 seconds per volume) visualization of cerebral vessels from axis to vertex at high spatial resolution (true voxel size, 1 x 1 x 2 mm). All 25 nidi detected at intraarterial DSA were visualized at time-resolved MR angiography. Intermodality agreement was excellent for arterial feeders (kappa = 0.91; 95% confidence interval [CI]: 0.786, 1.000) and venous drainage (kappa = 0.94; 95% CI: 0.814, 1.000) and was good for nidus size (kappa = 0.76; 95% CI: 0.562, 0.950).

CONCLUSION

The agreement (good to excellent) between time-resolved MR angiographic and DSA findings suggests that time-resolved MR angiography is a reliable tool for the characterization of intracranial AVMs with respect to arterial feeders, nidus size, and venous drainage.