Imaging soft x-rays using a microchannel plate

The GOLDHELOX Project is a student run project to construct a robotic solar telescope that will be used to take images of the sun in the soft X-ray region (171?181?) of the spectrum. The optical system uses a microchannel plate (MCP) detector. We tested the MCP to familiarize ourselves with and verify that MCP's can be used to image soft X-rays. Soft X-rays were created by a Manson source attached to a proportional counter to determine the amount of emitted X-rays detected by the MCP. The voltages on the MCP were varied to observe responses of varying voltage differences. Most of the observations were visible observations along with images made by a 35 mm camera with a telephoto lens. We found the 1000 V difference to produce the strongest and clearest images.     

The use of absorbers to optimize the surface dosage in treatment using ultrahard x-rays

The surface dose in megavoltage x-ray therapy can be modified using two different techniques: either varying the thickness of an absorber positioned directly on the surface of the patient or varying the distance to the surface of an absorber with constant thickness. Surface dose as a function of distance and absorber thickness has been measured at 4 MV and 8 MV x-rays. Both methods yield sufficiently and well-defined dose enhancements at the surface of the patient as desired clinically. The variation of the absorber-surface distance however has been proved to be the more simple and practicable method, offering the additional advantage of no contacting the patients skin.     

Measurement of depth dose curves of soft x-rays in a water phantom

A device is described which allows to perform dosimetry with a usual flat chamber made of plexiglas (PTW soft ray chamber) in the water phantom. The depth dose curves measured for anode potentials of 10 to 100 kV were compared to the curves measured a) in a plexiglas phantom, b) in a M3 phantom using a soft ray chamber made of M3, c) in a mixed phantom consisting of a plexiglas bottom, a soft ray chamber made of plexiglas flush with its surface, and plates or foils made of M3, polystyrene, and frapan. The results show that there is no difference between the depth dose curves measured in water and those measured in the homogeneous M3 phantom if the curve is plotted over the mass related to the surface (g/cm2). There is also no difference to the dose curve measured in the mixed phantom according to c) if M3 plates determining the depth of measurement are layed on it. With the other substances, considerable deviations are found. An example is presented in order to warn against the uncontrolled use of "plastic foils" as phantom material for soft ray depth dose curves.     

In-vivo quantification of dynamic hip joint center errors and soft tissue artifact

Hip joint center (HJC) measurement error can adversely affect predictions from biomechanical models. Soft tissue artifact (STA) may exacerbate HJC errors during dynamic motions. We quantified HJC error and the effect of STA in 11 young, asymptomatic adults during six activities. Subjects were imaged simultaneously with reflective skin markers (SM) and dual fluoroscopy (DF), an x-ray based technique with submillimeter accuracy that does not suffer from STA. Five HJCs were defined from locations of SM using three predictive (i.e., based on regression) and two functional methods; these calculations were repeated using the DF solutions. Hip joint center motion was analyzed during six degrees-of-freedom (default) and three degrees-of-freedom hip joint kinematics. The position of the DF-measured femoral head center (FHC), served as the reference to calculate HJC error. The effect of STA was quantified with mean absolute deviation. HJC errors were (mean ± SD) 16.6 ± 8.4 mm and 11.7 ± 11.0 mm using SM and DF solutions, respectively. HJC errors from SM measurements were all significantly different from the FHC in at least one anatomical direction during multiple activities. The mean absolute deviation of SM-based HJCs was 2.8 ± 0.7 mm, which was greater than that for the FHC (0.6 ± 0.1 mm), suggesting that STA caused approximately 2.2 mm of spurious HJC motion. Constraining the hip joint to three degrees-of-freedom led to approximately 3.1 mm of spurious HJC motion. Our results indicate that STA-induced motion of the HJC contributes to the overall error, but inaccuracies inherent with predictive and functional methods appear to be a larger source of error.     

Detection of malignant soft tissue tumors in bone imaging

A total of 2530 consecutive bone scans were examined to evaluate the number and the type of soft tissue neoplasms detected with bone-seeking phosphonates. Sixty-eight primary or secondary soft tissue neoplasms of 63 patients accumulated 99mTc -methylene diphosphonate and 2 accumulated 99mTc -diphosphonate, and one metastasis was seen as a nonactive 'cold' focus in the urinary bladder. The localization of tumors was: 19 in the lung, 15 in the liver, 11 in the kidney, 10 in the peritoneal cavity or ascites, 5 in the large bowel, 4 in the vascular or lymphatic system, 3 in the connective tissue or muscles, 2 in the ovary, 1 in the urinary bladder, and 1 in the brain. Our results differ in many respects from those reported in the literature. The causes of the differences are discussed.