Computed radiography versus indirect digital radiography for the detection of glass soft-tissue foreign bodies

Exploring the reliability of the exposure index with a range of kV and mAs values: An experimental study

INTRODUCTION

The exposure index (EI) is a numerical post-exposure tool that provides feedback to diagnostic radiographers undertaking digital X-ray examinations. The EI seeks to provide an indicator of the quantity of incident ionising radiation imparted on an image receptor. However, any large increase to X-ray intensity could interfere with the calculation of the EI. The aim of this paper was to evaluate detector overexposure by increasing X-ray beam intensity and quantifying the resultant effect on the EI.

METHODS

A porcine hip was purchased and exposed with varying tube potentials (50 to 110 kVp) and tube current-time products (5 to 100 mAs). Entrance surface dose (ESD) and EI values were determined for each exposure. For each acquisition parameter, two dose readings were collected. Linear regression was utilised to ascertain the relationship between the EI and varying tube exposures.

RESULTS

Tube exposures between 50 and 80 kVp demonstrated strong positive linear correlation coefficients (r = 0.993, p <0.001; r = 0.999, p <0.001; r = 0.983, p <0.001; r = 0.925, p <0.001) between ESD and EI. However, upon increasing tube exposures (90 to 110 kVp), interference with the EI calculation was demonstrated, which impacted both linearity, strength and direction of correlation (90 kVp r = 0.083, p = .248; 100 kVp r = -0.066, p = .479; 110 kVp r = -0.110, p = .601). Consequently, the use of higher tube exposures demonstrated variability with the EI by not demonstrating an expected positive linear relationship, which remained the initial expectation in this study.

CONCLUSION

The EI value is generally associated with providing reliable feedback to radiographers, yet this paper identifies some unexpected findings at high tube exposures (90 to 110 kVp). In short, this experiment provides insight that the EI value demonstrates inconsistent values within certain energy ranges.

IMPLICATIONS FOR PRACTICE

The findings have implications because it identifies variability of EI values at higher tube exposures. EI values may, therefore, not be helpful in providing meaningful feedback to radiographers when making changes to exposure factors.

Construction and validation of a low cost paediatric pelvis phantom

PURPOSE

Imaging phantoms can be cost prohibitive, therefore a need exists to produce low cost alternatives which are fit for purpose. This paper describes the development and validation of a low cost paediatric pelvis phantom based on the anatomy of a 5-year-old child.

METHODS

Tissue equivalent materials representing paediatric bone (Plaster of Paris; PoP) and soft tissue (Poly methyl methacrylate; PMMA) were used. PMMA was machined to match the bony anatomy identified from a CT scan of a 5-year-old child and cavities were created for infusing the PoP. Phantom validation comprised physical and visual measures. Physical included CT density comparison between a CT scan of a 5-year old child and the phantom and Signal to Noise Ratio (SNR) comparative analysis of anteroposterior phantom X-ray images against a commercial anthropomorphic phantom. Visual analysis using a psychometric image quality scale (face validity).

RESULTS

CT density, the percentage difference between cortical bone, soft tissue and their equivalent tissue substitutes were -4.7 to -4.1% and -23.4%, respectively. For SNR, (mAs response) there was a strong positive correlation between the two phantoms (r > 0.95 for all kVps). For kVp response, there was a strong positive correlation between 1 and 8 mAs (r = 0.85), this then decreased as mAs increased (r = -0.21 at 20 mAs). Psychometric scale results produced a Cronbach's Alpha of almost 0.8.

CONCLUSIONS

Physical and visual measures suggest our low-cost phantom has suitable anatomical characteristics for X-ray imaging. Our phantom could have utility in dose and image quality optimisation studies.