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A practical MRI-based reconstruction method for a new endocavitary and interstitial gynaecological template.

Richart J, Otal A, Rodriguez S, Nicolás AI, DePiaggio M, Santos M, Vijande J, Ballester F, Perez-Calatayud J - J Contemp Brachytherapy (2015)

Bottom Line: The differences observed in the positioning were significantly smaller than 1 mm in all cases.The presented algorithm also allows the use of only T2W sequence either for contouring or reconstruction purposes.The proposed method is robust and independent of the visibility of the artifact at the tip of the needle.

View Article: PubMed Central - PubMed

Affiliation: Radiotherapy Department, Benidorm Hospital, Benidorm, Alicante.

ABSTRACT

Purpose: There are perineal templates for interstitial implants such as MUPIT and Syed applicators. Their limitations are the intracavitary component deficit and the necessity to use computed tomography (CT) for treatment planning since both applicators are non-magnetic resonance imaging (MRI) compatibles. To overcome these problems, a new template named Template Benidorm (TB) has been recently developed. Titanium needles are usually reconstructed based on their own artifacts, mainly in T1-weighted sequence, using the void on the tip as the needle tip position. Nevertheless, patient tissues surrounding the needles present heterogeneities that complicate the accurate identification of these artifact patterns. The purpose of this work is to improve the titanium needle reconstruction uncertainty for the TB case using a simple method based on the free needle lengths and typical MRI pellets markers.

Material and methods: The proposed procedure consists on the inclusion of three small A-vitamin pellets (hyperintense on MRI images) compressed by both applicator plates defining the central plane of the plate's arrangement. The needles used are typically 20 cm in length. For each needle, two points are selected defining the straight line. From such line and the plane equations, the intersection can be obtained, and using the free length (knowing the offset distance), the coordinates of the needle tip can be obtained. The method is applied in both T1W and T2W acquisition sequences. To evaluate the inter-observer variation of the method, three implants of T1W and another three of T2W have been reconstructed by two different medical physicists with experience on these reconstructions.

Results and conclusions: The differences observed in the positioning were significantly smaller than 1 mm in all cases. The presented algorithm also allows the use of only T2W sequence either for contouring or reconstruction purposes. The proposed method is robust and independent of the visibility of the artifact at the tip of the needle.

No MeSH data available.


Example with poor visibility of artifact at the end of the needle
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Figure 0005: Example with poor visibility of artifact at the end of the needle

Mentions: During commissioning and using phantom measurements, one can well correlate the actual tip of the needle with the black signal produced at its end on MR images. This is done by registering CT and MR scans and finding the position of the needle tip according to its position found in the CT scan. The procedure has been previously described in the work by Haack et al. [13]. Titanium needles produce a clear and reproducible artefact pattern. They generate bright regions in both sides of the needles in a coronal view that can be used to locate the tip position. Nevertheless, unlike phantoms, patient tissues surrounding the needles present heterogeneities that complicate the accurate identification of these artifact patterns, see Figure 5. By using the method presented in this paper, this is not an issue, since it does not depend on the visibility of the artefact at the end of every needle.


A practical MRI-based reconstruction method for a new endocavitary and interstitial gynaecological template.

Richart J, Otal A, Rodriguez S, Nicolás AI, DePiaggio M, Santos M, Vijande J, Ballester F, Perez-Calatayud J - J Contemp Brachytherapy (2015)

Example with poor visibility of artifact at the end of the needle
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663216&req=5

Figure 0005: Example with poor visibility of artifact at the end of the needle
Mentions: During commissioning and using phantom measurements, one can well correlate the actual tip of the needle with the black signal produced at its end on MR images. This is done by registering CT and MR scans and finding the position of the needle tip according to its position found in the CT scan. The procedure has been previously described in the work by Haack et al. [13]. Titanium needles produce a clear and reproducible artefact pattern. They generate bright regions in both sides of the needles in a coronal view that can be used to locate the tip position. Nevertheless, unlike phantoms, patient tissues surrounding the needles present heterogeneities that complicate the accurate identification of these artifact patterns, see Figure 5. By using the method presented in this paper, this is not an issue, since it does not depend on the visibility of the artefact at the end of every needle.

Bottom Line: The differences observed in the positioning were significantly smaller than 1 mm in all cases.The presented algorithm also allows the use of only T2W sequence either for contouring or reconstruction purposes.The proposed method is robust and independent of the visibility of the artifact at the tip of the needle.

View Article: PubMed Central - PubMed

Affiliation: Radiotherapy Department, Benidorm Hospital, Benidorm, Alicante.

ABSTRACT

Purpose: There are perineal templates for interstitial implants such as MUPIT and Syed applicators. Their limitations are the intracavitary component deficit and the necessity to use computed tomography (CT) for treatment planning since both applicators are non-magnetic resonance imaging (MRI) compatibles. To overcome these problems, a new template named Template Benidorm (TB) has been recently developed. Titanium needles are usually reconstructed based on their own artifacts, mainly in T1-weighted sequence, using the void on the tip as the needle tip position. Nevertheless, patient tissues surrounding the needles present heterogeneities that complicate the accurate identification of these artifact patterns. The purpose of this work is to improve the titanium needle reconstruction uncertainty for the TB case using a simple method based on the free needle lengths and typical MRI pellets markers.

Material and methods: The proposed procedure consists on the inclusion of three small A-vitamin pellets (hyperintense on MRI images) compressed by both applicator plates defining the central plane of the plate's arrangement. The needles used are typically 20 cm in length. For each needle, two points are selected defining the straight line. From such line and the plane equations, the intersection can be obtained, and using the free length (knowing the offset distance), the coordinates of the needle tip can be obtained. The method is applied in both T1W and T2W acquisition sequences. To evaluate the inter-observer variation of the method, three implants of T1W and another three of T2W have been reconstructed by two different medical physicists with experience on these reconstructions.

Results and conclusions: The differences observed in the positioning were significantly smaller than 1 mm in all cases. The presented algorithm also allows the use of only T2W sequence either for contouring or reconstruction purposes. The proposed method is robust and independent of the visibility of the artifact at the tip of the needle.

No MeSH data available.