Determining the orientation angle of directional leads for deep brain stimulation using computed tomography and digital x-ray imaging: A phantom study

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Abstract

Purpose

Orientating the angle of directional leads for deep brain stimulation (DBS) in an axial plane introduces a new degree of freedom that is indicated by embedded anisotropic directional markers. Our aim was to develop algorithms to determine lead orientation angles from computed tomography (CT) and stereotactic x-ray imaging using standard clinical protocols, and subsequently assess the accuracy of both methods.

Methods

In CT the anisotropic marker artifact was taken as a signature of the lead orientation angle and analyzed using discrete Fourier transform of circular intensity profiles. The orientation angle was determined from phase angles at a frequency 2/360° and corrected for aberrations at oblique leads. In x-ray imaging, frontal and lateral images were registered to stereotactic space and sub-images containing directional markers were extracted. These images were compared with projection images of an identically located virtual marker at different orientation angles. A similarity index was calculated and used to determine the lead orientation angle. Both methods were tested using epoxy phantoms containing directional leads (Cartesia™ Boston Scientific, Marlborough, USA) with known orientation. Anthropomorphic phantoms were used to compare both methods for DBS cases.

Results

Mean deviation between CT and x-ray was 1.5° ± 3.6° (range: −2.3° to 7.9°) for epoxy phantoms and 3.6° ± 7.1° (range: −5.6° to 14.6°) for anthropomorphic phantoms. After correction for imperfections in the epoxy phantoms, the mean deviation from ground truth was 0.0° ± 5.0° (range: −12° to 14°) for x-ray. For CT the results depended on the polar angle of the lead in the scanner. Mean deviation was −0.3° ± 1.9° (range: −4.6° to 6.6°) or 1.6° ± 8.9° (range: −23° to 34°) for polar angles ≤ 40° or > 40°

Conclusions

The results show that both imaging modalities can be used to determine lead orientation angles with high accuracy. CT is superior to x-ray imaging, but oblique leads (polar angle > 40°) show limited precision due to the current design of the directional marker.

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