[Optimal beam quality for chest digital radiography]

[Usefulness of Copper Filter Addition and Potential for Dose Reduction in Hip-joint Radiography]

PURPOSE

In this study, we evaluated image quality and radiation dose reduction when a Copper (Cu) filter was added to hip joint X-ray imaging.

METHODS

We measured effective energy without (0 mm) and with (0.1/0.2 mm) Cu-added filter at 70 kV, and we calculated soft tissue-bone contrast and signal-difference-to-noise-ratio (SDNR) under constant entrance surface dose. After that, we estimated the dose reduction rate.

RESULTS

The effective energy was 32.07 keV for 0 mm Cu, 37.59 keV for 0.1 mm Cu, and 40.91 keV for 0.2 mm Cu. As the thickness of the Cu-added filter was increased, contrast decreased, but SDNR increased. The dose reduction rate in bone calculated measuring SDNR was 34% for 0.1 mm Cu and 47% for 0.2 mm Cu in max.

CONCLUSION

It was suggested that adding Cu filter to hip-joint X-ray imaging could reduce entrance surface dose while maintaining the image quality based on SDNR.

[Subjective Contrast of Pulmonary Tissues in CsI-FPD Chest Radiography Using Model Phantom by Monte Carlo Simulation]

OBJECTIVE

Subject contrast of pulmonary tissues was investigated for five X-ray beams (70 kV without filter, 90 kV with 0.15 mm Cu filter, 90 kV with 0.2 mm Cu filter, 120 kV without filter, and 120 kV with 0.2 mm Cu filter) in CsI-FPD chest radiography using two types of model phantoms by Monte Carlo simulation.

METHODS

A total of 72 million photons were entered to the model lung phantom (width, 300 mm; length, 300 mm; thickness, 200 mm; air space, 120 mm) and model mediastinum phantom (width, 300 mm; length, 300 mm; thickness, 200 mm; air space, 40 mm). Individual primary and secondary photon's process (absorption, scattering, and penetration) in the phantom and CsI-detector was recorded by Monte Carlo simulation. Subject contrast was calculated by entered and absorbed photon's number in the CsI-detector.

RESULTS

Subject contrast pulmonary tissues were high to low energy X-ray beam; however, the ones of soft tissue and soft tissue overlaying bone had few differences for beam quality except 70 kV without filter. Moreover, the subject contrast by absorbed photons was higher compared to the one by entered photons in CsI.

CONCLUSION

It was shown that the subject contrast study by Monte Carlo calculation can be replaced by the way of physical chest phantom, and that the subject contrast by absorbed photons and by injected photons in CsI was different. Furthermore, be verified that the subject contrast of soft tissue and soft tissue overlaying bone differs hardly.

[Study of X-ray Beam Quality and Contrast-to-Noise Ratio of Lung Nodules in Chest FPD Radiography: Monte Carlo Simulation Using Chest Model Phantom]

OBJECTIVES

Contrast-to-noise ratio (CNR) of four X-ray beams (90 kV with 0.15-mm Cu filter, 90 kV with 0.2-mm Cu filter, 120 kV without filter and 120 kV with 0.2-mm Cu filter) in CsI-flat panel detector (FPD) radiography for lung cancer diagnosis was investigated using Monte Carlo simulation.

METHOD

Two billion photons were injected to the chest phantom model (width: 300 mm, length: 300 mm, thickness: 200 mm) with imitated lung nodules (10 mm diameter, CT value: +30 Hounsfield unit (HU), -375 HU, and -620 HU). Individual primary and secondary photon's process (absorption, scattering and penetration) in the phantom and CsI-detector was recorded by Monte Carlo simulation. CNR was calculated using primary and secondary absorbed photon's number in the CsI-detector.

RESULTS

CNR of 90 kV X-ray beam with 0.15 mm and 0.2 mm Cu filters was higher to 120 kV X-ray beam because of higher primary object contrast and photon's contribution, and high photon's absorption to CsI.

CONCLUSION

By Monte Carlo calculation, it was verified that 90 kV X-ray beam with 0.15 mm and 0.2 mm Cu filters yielded higher CNR to 120 kV X-ray beam.