Johnsrud Kjersti, Skretting Arne, Naum Alexandru G, Bogsrud Trond V, Bach-Gansmo Tore
Department of Radiology and Nuclear medicine, Oslo University Hospital, Oslo, Norway.
Clin Physiol Funct Imaging. 2013 Nov;33(6):478-82. doi: 10.1111/cpf.12057. Epub 2013 Jun 12.
The aim of the study was to investigate a new principle for collimation of gamma probes for radioguided surgery and sentinel node detection: the use of asymmetric lateral shielding. The intension was to maintain the sensitivity in the lateral and forward directions on the unshielded side while at the same time to shield the probe against high activity sources that could mask the signal from the object to be detected.
The device was constructed to shield only against photons that come from a region in space that spans approximately 180° sideways and forwards relative to the detector. The intension of the study was to demonstrate the principle rather than to document its use in the clinic. Sensitivity profiles were derived from measurements obtained while stepwise moving the probe relatively to a point source of known activity surrounded by water. The measurements were taken in the symmetry plane of the collimator where the shielding effects were expected to be most pronounced.
The asymmetric collimator led to nearly unchanged sensitivity in the lateral and forward directions. At the same time, the field of view was effectively shrunk on the shielded side. Contributions from sources lateral and close to the shield were reduced by factors up to 45.
By rotating the probe around its longitudinal axis, an asymmetric add-on shield collimator could potentially make it easier to detect a sentinel node when this is located close to a neighbouring high activity region like the urinary bladder or the injection site.
本研究的目的是探讨一种用于放射性引导手术和前哨淋巴结检测的γ探测器准直新原理：使用不对称侧向屏蔽。其目的是在未屏蔽侧保持侧向和向前方向的灵敏度，同时屏蔽探测器免受可能掩盖待检测物体信号的高活度源的影响。
该装置被设计成仅屏蔽来自相对于探测器在空间中侧向和向前约180°范围内区域的光子。本研究的目的是证明该原理，而非记录其在临床中的应用。灵敏度曲线是通过将探测器相对于被水包围的已知活度点源逐步移动时获得的测量值推导得出的。测量在准直器的对称平面进行，预计屏蔽效果在此最为明显。
不对称准直器使侧向和向前方向的灵敏度几乎保持不变。同时，屏蔽侧的视野有效缩小。来自侧向且靠近屏蔽的源的贡献降低了多达45倍。
当在前哨淋巴结靠近如膀胱或注射部位等高活度相邻区域时，通过绕探测器纵轴旋转，不对称附加屏蔽准直器可能会使前哨淋巴结的检测变得更容易。
