放射治療標誌物在多模式影像之可視性及假影分析

Fiducial markers visibility and artifacts in multi- modality imaging

張慎分(Shen-Fen Chang)

指導教授 ： 莊濬超

中山醫學大學/醫學科技學院/醫學影像暨放射科學系/碩士(2021年)

https://doi.org/10.6834/csmu202100157

摘要

目的：
在癌症的放射治療中，當使用影像上可見的標誌物時，影像導引放射治療前的位置校準能夠得到改善。
由於先前研究提到CoHA(Cobalt- Hydroxyapetite)是適合作為放射治療的標誌物的，而得知BG(Bioglass)在體內會生成氫氧基磷灰石的特性，並且其中BG在影像上的不透射性是由氧化鈉及氧化鈣提供，在此基礎上將鈣元素用鈷來替換，可使不透射性增加，期望讓此材質在一般放射線影像下可視性更高。本篇將會使用CoBG(Cobalt- Bioglass)來研究是否同樣適合作為放射治療的標誌物。
材料與方法：
本研究使用了臨床使用的5個標誌物(PointCoilTM(POINT)、CyberMarkTM(CYBER)、Gold Soft Tissue Markers(ST)、Bone Markers(BONE)、PolyMarkTM(POLY))及兩個自製標誌物(CoBG、BG)以平放及插入兩種狀態放入明膠假體中，以電腦斷層、錐束電腦斷層、磁振造影、電子照野驗證系統(EPID)影像及一般診斷X光影像來造影分析。針對影像失真，利用測量影像上標誌物長度及面積來評估。對於電腦斷層及磁振造影影像，利用SI(假影指標)和MAI(金屬假影指標)來評估假影。CNR及CBR用於評估三維以及二維影像之可視性。
結果：
電腦斷層影像中，CoBG相較於其他標誌物有較小的放大率，約1.3倍，SI值也比假影最嚴重的標誌物少了至少十倍，並且在經過MAR處理後(6.56mm2)，與未使用MAR處理測得的面積(7.32mm2)相似，代表CoBG在CT影像上並未造成過多的金屬假影，這與SI值的結果相呼應。
MRI影像的放大程度在1.5T時平放狀況下除了POLY和CoBG在T1 MPRAGE波序下長度有較明顯的放大，分別為2.59±0.43(2.6倍)、6.66±0.20(2.4倍)，其餘約1.2至2倍左右，插入狀況下約1.1倍左右。MRI影像上面積測量數據中，CoBG不論在哪個擺放方向、磁場強度或是波序下皆有最大的放大率，在所有標誌物裡，只有CoBG是在不同磁場強度及不同波序下MAI皆大於1%，代表CoBG在MRI影像上是產生了非常嚴重的假影。
EPID影像之CBR大於2被認定為能辨別的，POLY、CoBG及BG之CBR不論是平放或插入狀況皆小於2，此數據結果與影像是相符的，使用一般診斷X光攝影時，所有標誌物都是能夠容易辨認的。
結論：
在電腦斷層影像上，CoBG有很好的表現，包括了好的可視性及少量的假影，但在使用MRI造影時，會造成非常嚴重的假影，而對於EPID影像則是沒有可視性的，期望未來可以利用其他材料替代掉鈷以更提高原子序。並且避免MRI影像假影。

關鍵字

影像導引放射治療 ； 放射治療標誌物 ； 電腦斷層 ； 磁振造影

並列摘要

Purpose
In radiotherapy, when using a visible fiducial markers on the image, the position alignment before image-guided radiotherapy can be improved.
Since previous studies mentioned that CoHA (Cobalt-Hydroxyapetite) is suitable as a marker for radiotherapy, it is known that BG (Bioglass) can generate hydroxylapatite in the body. On this basis, replacing the calcium with cobalt can increase the radiopacity. It is hoped that this material will be more visible under radiographic images. In this study, we will use CoBG (Cobalt-Bioglass) to study whether it is also suitable as a fiducial marker for radiotherapy.
Materials and Methods
This study used 5 clinical fiducial markers and two self-made markers . The markers are placed in two situation in gelatin phantom, and analyzed by CT, CBCT, MRI, EPID and general diagnostic X-ray images. For evaluate the image distortion, use the length and area of the marker on the image. For CT and MRI images, SI (Streak Artifact Index) and MAI (Metal Artifact Index) are used to evaluate artifacts. CNR and CBR are used to evaluate the visibility of 3D and 2D images.
Result
In the CT image, CoBG has a smaller magnification than other markers, about 1.3 times, and the SI value is at least ten times less than that the marker with the most serious artifacts. After MAR processing, which measured area is similar to the without MAR processing image. It means that CoBG did not cause excessive metal artifacts on the CT image, which corresponds to the result of the SI value.
The magnification of MRI images is about 1.2 to 2 times, but
2.6 times and 2.4 times in the perpendicular position for POLY and CoBG under the T1 MPRAGE sequence, and about 1.1 times in the parallel position. In the area measurement data on MRI images, CoBG has the largest magnification regardless of its placement direction, magnetic field strength, or sequence. In all markers, only CoBG has the MAI that is greater than 1% under different magnetic field strengths and sequences. It means that CoBG has produced a very serious artifact on the MRI image.
EPID images whose CBR is greater than 2 are indicated clear visibility. The CBR of POLY, CoBG and BG is less than 2 whether it is placed perpendicular or parallel. When using general diagnostic X-ray photography, all markers are easily identifiable.
Conclusion
On CT image, CoBG has a good performance, including good visibility and a least artifacts, but when using MRI imaging, it will cause very serious artifacts, and there is no visibility for EPID images. It is hoped that in the future, other materials can be used to replace cobalt to further improve the atomic number. And to avoid MRI image artifacts.

並列關鍵字

IGRT ； Fiducial Marker ； CT ； MRI

參考文獻

參考文獻

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