Radiographic detail and variation of the nominal focal spot size: the "focal effect"

Can the anode heel effect be used to optimise radiation dose and image quality for AP pelvis radiography?

INTRODUCTION

A study was conducted to determine whether the anode heel effect can be used to influence optimisation of radiation dose and image quality (IQ) for AP pelvis radiography.

METHODS

ATOM dosimetry phantom and an anthropomorphic phantom were positioned for AP pelvis. Using a CR system, images were acquired and doses were measured with phantom feet toward anode and then feet toward cathode. Exposure factors (kVp, mAs and SID) were systematically generated using a factorial design. Images were scored visually for quality using relative visual grading together with a 3 point Likert scale. Signal to noise ratio was also calculated as a physical measure of image quality. Dosimetry data were collected for the ovaries and testes.

RESULTS

The optimum technique for male, which resulted in lower dose and suitable image quality, was with feet positioned toward the anode (0.80 ± 0.03 mGy; SNR of 38 ± 2.9; visual IQ score 3.13 ± 0.35). The optimum technique for female was with feet toward anode (0.23 ± 0.02 mGy; SNR of 34.7 ± 2.6; visual IQ score 3.15 ± 0.26). kVp had the biggest effect on both visual and physical image quality metrics (p < 0.001) for both tube orientations, whereas SID had the lowest effect on both visual and physical image quality metrics compared with mAs and kVp (p < 0.001). The effect of SID on the SNR was not significant (p > 0.05) with feet toward anode.

CONCLUSION

Positioning the patient with feet toward the anode, as opposed to the cathode, has no adverse effect on visual image quality assessment but it does have an effect on physical image quality.

IMPLICATIONS FOR PRACTICE

This study would add a new clinical concept in positioning of AP pelvis radiography especially for male positioning.

The reliability of measurements taken from radiographs in the assessment of paediatric flat foot deformity

BACKGROUND

Radiographic charted values are widely applied in the assessment of paediatric flat foot and as quantitative markers of intervention success. Nearly all literature pertaining to the reliability of these measures relates to the adult foot. In view of the importance placed on these charted values we assessed the inter and intra-rater reliability of 10 key radiographic measures in children aged 7-14 years.

METHODS

We present the reliability of these measures in terms of intra class correlation and standard error based on repeated measures of 50 radiographs across five independent trained observers. Two new detailed methods are presented for the calculation of lateral and dorso-plantar talo-calcaneal overlap in an attempt to better define the talo-calcaneal inter-relationship.

RESULTS

The results demonstrate wide variation of measurement reliability, with some measures being highly reproducible and others showing poor reproducibility. A strong negative correlation between reliability and the number of steps required for the measurement was demonstrated. Consistent with other studies intra-rater reliability tended to be higher than that of inter-rater reliability.

CONCLUSION

In conclusion, we have provided evidence as to which radiographic charted measures may be reliably used in evaluating the paediatric flat foot in children aged 7-14 years, and which measures are not reliable and we advise against their application.

X-ray tubes--continuous innovative technology

The X-ray tube is one of the most important components in any X-ray system. In the beginning, physicists and physicians used gas ion tubes. The so-called Coolidge tube applied a high vacuum and is still used today. Medical examinations have required continuously improved designs of X-ray tubes (smaller focal spots at a higher output). The principle of the Goetze line focus is still applied in any diagnostic X-ray tube. Different anode materials and the rotating anode contributed to an increased output and reduced exposure time. Bearings needed special attention. Spiral groove bearings are the most advanced design today. The heat storage capacity of the anode and the tube housing assembly influences examination time and patient throughput. Cardiac imaging required less motion blurring in cine film images and increasing radiation exposure in interventional procedures called for measures to reduce dose. Protection against radiation and electric shock has always been a concern of design engineers. Focal spot sizes dedicated to specific applications and heat management within the total tube housing assembly will be future issues. Even with the event of ultrasound and MR technology, X-ray procedures will still be applied for diagnostic and interventional purposes.