Basic evaluation of a single probe system for lymph node detection with F-18 FDG

研制的γ探测系统由直径9mm的NaI（T1）探测器、数据采集器、中央处理器和数据显示器组成。我们为Tc-99 m制作了两种不同的钨准直器：一种是长40 mm、直径9mm、壁厚3.5mm的直孔;准直器尖端和探测器之间的距离在0到20 mm之间变化。另一种是锥形头，直径在5 mm距离内从8 mm减小到3 mm。准直器尖端与探测器表面之间的距离在5 mm至20 mm之间变化。为F-18战斗机研制了两种不同类型的钨准直器：一种是直径9mm、长33 mm、厚10 mm的直孔式钨准直器;另一种是尖端逐渐变细的，尖端直径为3 mm，距尖端5 mm处直径为9mm，长度为23 mm，厚度为10 mm。用Tc-99 m和F-18研究了系统的计数率性能。得到了各准直器在水中的响应曲线。在每个准直器中确定两个点源的最小区分。在F-18的探测器系统中，检测到511 keV光子的侧向穿透，两种核素的活度与计数在35 kcps以内呈线性关系。直孔准直器在水中的灵敏度迅速下降：在20 mm深度处为70%。使用锥形准直器，在水中的灵敏度损失是逐渐的：在40 mm处为80%。锥形准直器的最小区分能力为20 mm，直孔准直器的最小区分能力为180 mm。511 keV光子的侧向穿透率小于10%，可作为F-18 FDG前哨淋巴结或淋巴结转移灶检测的辅助手段。

The gamma probe system developed consists of a NaI(T1) detector 9mm in diameter, a data acquisition unit ,central processing unit and data display unit. Two different kinds of tungsten collimators were constructed for Tc-99m: One is a straight bore of 40mm in length, 9mm in diameter and 3.5mm in wall thickness. The distance between the tip of the collimator and the detector is variable from 0 to 20mm. The other is a one with tapered tip, the diameter decreasing from 8mm to 3mm within 5mm distance. The distance between the tip of the collimator and the surface of the detector is variable from 5mm to 20mm. Two different types of tungsten collimator for F-18 were constructed: One is a straight bore type of 9mm in diameter, 33mm in length and 10mm in thickness. The other is one with tapering tip; 3mm in the tip diameter, 9mm in diameter at the 5mm from the tip, 23mm in length and 10mm in thickness. The counting rate performance of the system was studied with Tc-99m and F-18. The response curve of each collimator in water was obtained. Minimum differentiation of two point sources was determined in each collimator. The side penetration of 511keV photon was checked in the detector system for F-18.There was linear relationship between activities and counts up to 35kcps for both nuclides. The sensitivity in water was rapidly decreased with the straight bore collimator: 70% at the depth of 20mm. With the tapering collimator the sensitivity loss in water was gradual: 80% at 40mm. The minimum differentiation capability was 20mm with the tapering collimator and 180mm with straight bore collimator. The side penetration of 511keV photon was less than 10%.These results indicate that this system may be a useful aid for sentinel node detection or lymph node metastasis detection with F-18 FDG.