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

研制的伽马探头系统由直径9 mm的NaI(T1)探测器、数据采集单元、中央处理单元和数据显示单元组成。研制了两种不同类型的钨准直器：一种是长40 mm、直径9 mm、壁厚3.5 mm的直孔。准直器顶端和探测器之间的距离在0到20 mm之间变化。另一种是锥形尖端，直径在5 mm内从8 mm减小到3 mm。准直器顶端与探测器表面之间的距离在5 mm到20 mm之间变化。为F-18建造了两种不同类型的钨准直器：一种是直径9 mm、长33 mm、厚10 mm的直孔式准直器。另一种是锥形尖端，尖端直径3 mm，距尖端5 mm处直径9 mm，长23 mm，厚10 mm。用~(99m)Tc和~(18)F研究了该体系的计数率性能。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差值。在F-18探测器系统中检查了511keV光子的侧面穿透。两种核素的活度和计数之间都有线性关系，最高可达35kcps。直孔准直器在水中的灵敏度在20 mm处迅速降低了70%。对于锥形准直器，在水中的灵敏度损失是逐渐的：在40 mm处灵敏度损失为80%。锥形准直器最小分辨能力为20 mm，直孔准直器最小分辨能力为180 mm。511keV光子的侧面穿透率小于10%。这一结果表明，该系统可用于前哨淋巴结的检测或F-18FDG的淋巴转移检测。

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.