Francis Zarb

AP diameter shows the strongest correlation with CTDI and DLP in abdominal and chest CT

The purpose of this study is to investigate the relationships among cross-sectional diameters, weight and computed tomography (CT) dose descriptors (CTDI and DLP) to identify which is best used as a measure for the establishment of DRLs in CT. Data (gender, weight, cross-sectional diameters, dose descriptors) from 56 adult patients attending for either a CT examination of the abdomen or chest was obtained from two spiral CT units using automatic milliampere modulation. The AP diameter was demonstrated as the main contributing factor influencing the dose in CT (CTDI: r(2) = 0.269, p-value < or =0.001; DLP: r(2) = 0.260, p-value < or =0.001) since it has a greater correlation with radiation dose than body weight and can thus be its substitute in dose-reduction strategies and establishment of DRLs. The advantages of using the AP diameter are that it can easily be measured prior to scanning or retrospectively from previous CT images. However, further studies on the practicality of this approach are recommended.

Negative Poisson's ratios in tendons: An unexpected mechanical response.

UNLABELLED Tendons are visco-elastic structures that connect bones to muscles and perform the basic function of force transfer to and from the skeleton. They are essential for positioning as well as energy storing when involved in more abrupt movements such as jumping. Unfortunately, they are also prone to damage, and when injuries occur, they may have dilapidating consequences. For instance, there is consensus that injuries of tendons such as Achilles tendinopathies, which are common in athletes, are difficult to treat. Here we show, through in vivo and ex vivo tests, that healthy tendons are highly anisotropic and behave in a very unconventional manner when stretched, and exhibit a negative Poissons ratio (auxeticity) in some planes when stretched up to 2% along their length, i.e. within their normal range of motion. Furthermore, since the Poissons ratio is highly dependent on the materials microstructure, which may be lost if tendons are damaged or diseased, this property may provide a suitable diagnostic tool to assess tendon health. STATEMENT OF SIGNIFICANCE We report that human tendons including the Achilles tendons exhibits the very unusual mechanical property of a negative Poissons ratio (auxetic) meaning that they get fatter rather than thinner when stretched. This report is backed by in vivo and ex vivo experiments we performed which clearly confirm auxeticity in this living material for strains which correspond to those experienced during most normal everyday activities. We also show that this property is not limited to the human Achilles tendon, as it was also found in tendons taken from sheep and pigs. This new information about tendons can form the scientific basis for a test for tendon health as well as enable the design of better tendon prosthesis which could replace damaged tendons.

A multi-phased study of optimisation methodologies and radiation dose savings for head CT examinations

The impact of optimisation methods on dose reductions for head computerised tomography was undertaken in three phases for two manufacturer models. Phase 1: a Catphan(®)600 was employed to evaluate protocols where the impact of parameter manipulation on dose and image quality was gauged by psychophysical measurements of contrast and spatial resolution in terms of contrast discs and line pairs. mA, kV and pitch were systematically altered until the optimisation threshold was identified. Phantom studies provide dose comparisons during optimisation but lack anatomical detail. Phase 2: optimised protocols were tested on a porcine model permitting further dose reductions over phantom findings providing anatomical structures for image quality evaluation using relative visual grading analysis of anatomical criteria. Phase 3: patient images using pre- and post-optimised protocols were clinically audited using visual grading characteristic analysis and ordinal regression analysis providing a robust analysis of image quality data prior to clinical implementation.

AN INVESTIGATION INTO CT RADIATION DOSE VARIATIONS FOR HEAD EXAMINATIONS ON MATCHED EQUIPMENT

This study investigated radiation dose and image quality differences for computed tomography (CT) head examinations across centres with matched CT equipment. Radiation dose records and imaging protocols currently employed across three European university teaching hospitals were collated, compared and coded as Centres A, B and C from specification matched CT equipment models. Patient scans (n = 40) obtained from Centres A and C were evaluated for image quality, based on the visualisation of Commission of European Community (CEC) image quality criteria using visual grading characteristic (VGC) analysis, where American Board of Radiology examiners (n = 11) stated their confidence in identifying anatomical criteria. Mean doses in terms of CT dose index (CTDIvol-mGy) and dose length product (DLP-mGy cm) were as follows: Centre A-33.12 mGy and 461.45 mGy cm; Centre B -101 mGy (base)/32 mGy (cerebrum) and 762 mGy cm and Centre C-71.98 mGy and 1047.26 mGy cm, showing a significant difference (p ≤ 0.05) in DLP across centres. VGC analysis indicated better visualisation of CEC criteria on Centre C images (VGCAUC 0.225). All three imaging protocols are routinely used clinically, and image quality is acceptable in each centre. Clinical centres with identical model CT scanners have variously customised their protocols achieving a range of dose savings and still resulting in clinically acceptable image quality.

The impact of breast size on mean lung dose for patients receiving tangential radiotherapy to the whole breast

Purpose To explore the impact of breast size on mean lung dose (MLD) for patients receiving breast radiotherapy. Methodology Chest wall separation (CWS), volume of tissue receiving 95% isodose and MLD were measured on 80 radiotherapy treatment plans of patients receiving tangential radiotherapy treatment to the whole breast. Breast size was categorised as small (CWS 25 cm and PTV>1500 cm3). Pearson’s correlation and independent sample t-test were used to analyse data. Results MLD was not affected by CWS (r=−0·13, p=0·24) nor volume of tissue receiving 95% isodose (r=−0·08, p=0·49). Significant variation between small and large breasts was noted for CWS (t=8·24, p=0·00) and volume of tissue receiving 95% isodose (t=5·68, p=0·00). No significant variation was noted between small and large breast for MLD (t=−0·26, p=0·80) and between left and right breasts for CWS (t=1·42, p=0·16) and volume of tissue receiving 95% isodose (t=−1·08, p=0·28). Significant difference between left (18–808 cGy) and right breast (325–365 cGy) was demonstrated for MLD (t=3·03, p=0·00). Conclusion This study demonstrated lack of correlation between breast size and MLD. Further research is recommended for justification of alternative techniques for this subgroup of patients to provide optimised radiotherapy delivery.