ASSESSMENT OF OCCUPATIONAL EXPOSURE IN THE MAIN PAEDIATRIC INTERVENTIONAL RADIOLOGY PROCEDURES.

The aim of this study is to evaluate the personal dose equivalent Hp(10) in the most frequent (non-cardiac) paediatric interventional radiology (PIR) procedures: central venous catheters (CVC), hepatic/biliary and sclerotherapy interventions. i2 active solid-state dosemeters placed over the lead apron were used to monitor the exposure of three interventional radiologists over 18 months. A database was created to register all procedures performed by each radiologist (including the type of procedure and the kerma-area product, PKA). The mean Hp(10) per procedure for CVC, sclerotherapy and hepatic/biliary interventions was respectively 0.01 ± 0.01 mSv, 0.18 ± 0.13 mSv and 0.12 ± 0.06 mSv (k = 2). A similar value of Hp(10)/PKA was found despite the type of procedure or the patient weight (~10 µSv/Gy·cm2). There was high variability among individual interventions, probably due to the variable level of complexity, which led to uncertainties in the measurements' mean higher than those associated with the dosemeter's angular and energy dependence. i2 therefore proved suitable for monitoring Hp(10) in PIR procedures.

Role of correlated noise in textural features extraction.

Predictive models of tumor response based on heterogeneity metrics in medical images, such as textural features, are highly suggestive. However, the demonstrated sensitivity of these features to noise does affect the model being developed. An in-depth analysis of the noise influence on the extraction of texture features was performed based on the assumption that an improvement in information quality can also enhance the predictive model. A heuristic approach was used that recognizes from the beginning that the noise has its own texture and it was analysed how it affects the quantitative signal data. A simple procedure to obtain noise image estimation is shown; one which makes it possible to extract the noise-texture features at each observation. The distance measured between the textural features in signal and estimated noise images allows us to determine the features affected in each observation by the noise and, for example, to exclude some of them from the model. A demonstration was carried out using synthetic images applying realistic noise models found in medical images. Drawn conclusions were applied to a public cohort of clinical images obtained using FDG-PET to show how the predictive model could be improved. A gain in the area under the receiver operating characteristic curve between 10 and 20% when noise texture information is used was shown. An improvement between 20 and 30% can be appreciated in the estimated model quality.

Occupational doses to the eye lens in pediatric and adult noncardiac interventional radiology procedures.

PURPOSE: To assess occupational lens exposure in a mixed interventional radiology department, comparing pediatric and adult procedures. To analyze the correlation between the lens dose and the doses measured at the chest and collar level and the kerma-area product (PKA ). METHODS: For 17 months, three radiologists performing both pediatric and adult interventions were monitored by means of 14 dosimeters per worker: 12 single-point optically stimulated luminescent (OSL) dosimeters calibrated in terms of Hp (0.07) were placed on the inside and outside of two pairs of lead glasses, one for pediatric procedures and one for adult interventions; another whole-body OSL dosimeter calibrated in terms of Hp (10) was placed over the thyroid shield; finally, an additional active solid-state dosimeter, also calibrated for Hp (10), was worn on the chest, over the apron. Furthermore, a database was created to register the demographic and dosimetric data of the procedures, as well as the name of the radiologist acting as first operator. RESULTS: For the three radiologists, who performed 276-338 procedures/year (20% pediatric), cumulative annual doses to the left bare eye exceeded 20 mSv (21-61 mSv). Considering the glasses' protection, annual doses exceeded 6 mSv (13-48 mSv) for both eyes. No important differences were observed in lens dose per procedure between pediatric and adult interventions (0.16 vs 0.18, 0.12 vs 0.09, and 0.07 vs 0.07 mSv), although lens dose per PKA was 4.1-4.5 times higher in pediatrics (5.8 vs 1.3, 3.3 vs 0.8, and 2.6 vs 0.6 µSv/Gy·cm2 ) despite a similar use of the ceiling-suspended screen. Lens doses were highly correlated with collar readings (with Pearson coefficients [r] ranging from 0.86 to 0.98) and with chest readings (with r ranging from 0.75 to 0.93). However, slopes of the linear regressions varied greatly among radiologists. CONCLUSIONS: There is real risk of exceeding the occupational dose limit to the eye lens in mixed interventional radiology rooms if radiation protection tools are not used properly. Regular monitoring of the lens dose is recommended, given lens exposure might easily exceed 6 mSv/yr. Using a collar dosimeter for this purpose might be suitable if it is preceded by an individualized regression analysis. The same radiation protection measures should be applied to interventional radiologists regardless of whether they are treating pediatric or adult patients.

Local diagnostic reference levels for paediatric non-cardiac interventional radiology procedures.

PURPOSE: To establish local diagnostic reference levels (DRLs) for non-cardiac interventional procedures in paediatrics. METHODS: The type of procedure, the patient's weight and age and dose-related data from 279 interventions was recorded in a database completed by interventional radiologists, radiographers and technicians of the Medical Physics department. These procedures were classified into 14 categories and 6 weight ranges. Local DRLs were proposed for those ranges in which a sample of at least 15 patients could be gathered and were calculated as the third quartile (Q3) of the air kerma-area product (PKA) values. The Q3 of the fluoroscopy time (FT) and number of digital subtraction angiography (DSA) images were also obtained. Finally, the correlation between PKA and weight was analysed. RESULTS: Local DRLs are proposed for three types of procedures: hepatic/biliary interventions (5-15 kg, 1304 cGy·cm2; 15-30 kg, 2121 cGy·cm2), sclerotherapy procedures (15-30 kg, 704 cGy·cm2; 30-50 kg, 4049 cGy·cm2; 50-80 kg, 3734 cGy·cm2) and central venous catheter (CVC) procedures (5-15 kg, 84 cGy·cm2). Hepatic/biliary interventions showed a moderate correlation (r = 0.61), while sclerotherapy procedures presented a poor correlation (r = 0.34) between PKA and weight, possibly due to the PKA dependence on the complexity level. Regarding CVC procedures, a clearly higher correlation was found when the fluoroscopy PKA value was normalised to the FT (r = 0.85 vs r = 0.35). CONCLUSIONS: The results support the feasibility of establishing DRLs for the most common procedures (sclerotherapy, hepatic/biliary and CVC interventions) despite the small number of paediatric interventions.

Segmentation improvement through denoising of PET images with 3D-context modelling in wavelet domain.

Positron emission tomography (PET) images have been incorporated into the radiotherapy process as a powerful tool to assist in the contouring of lesions, leading to the emergence of a broad spectrum of automatic segmentation schemes for PET images (PET-AS). However, not all proposed PET-AS algorithms take into consideration the previous steps of image preparation. PET image noise has been shown to be one of the most relevant affecting factors in segmentation tasks. This study demonstrates a nonlinear filtering method based on spatially adaptive wavelet shrinkage using three-dimensional context modelling that considers the correlation of each voxel with its neighbours. Using this noise reduction method, excellent edge conservation properties are obtained. To evaluate the influence in the segmentation schemes of this filter, it was compared with a set of Gaussian filters (the most conventional) and with two previously optimised edge-preserving filters. Five segmentation schemes were used (most commonly implemented in commercial software): fixed thresholding, adaptive thresholding, watershed, adaptive region growing and affinity propagation clustering. Segmentation results were evaluated using the Dice similarity coefficient and classification error. A simple metric was also included to improve the characterisation of the filters used for induced blurring evaluation, based on the measurement of the average edge width. The proposed noise reduction procedure improves the results of segmentation throughout the performed settings and was shown to be more stable in low-contrast and high-noise conditions. Thus, the capacity of the segmentation method is reinforced by the denoising plan used.

Denoising of PET images by context modelling using local neighbourhood correlation.

Positron emission tomography (PET) images are characterised by low signal-to-noise ratio and blurred edges when compared with other image modalities. It is therefore advisable to use noise reduction methods for qualitative and quantitative analyses. Given the importance of the maximum and mean uptake values, it is necessary to avoid signal loss, which could modify the clinical significance. This paper proposes a method of non-linear image denoising for PET. It is based on spatially adaptive wavelet-shrinkage and uses context modelling, which explicitly considers the correlation between neighbouring pixels. This context modelling is able to maintain the uptake values and preserve the edges in significant regions. The algorithm is proposed as an alternative to the usual filtering that is performed after reconstruction.