LEAD COMPOSITE VS. NONLEAD PROTECTIVE GARMENTS: WHICH ARE BETTER? A MULTIVENDOR COMPARISON.

This study aims to provide more insight in attenuation characteristics and corresponding lead (Pb) equivalences of a broad range of commercially available lead composite and nonlead protective garments. Thirty garments of five manufacturers (listed as 0.25-0.35-0.50 mm Pb equivalent) were tested. Transmission values were determined at 70, 90 and 110 kVp using an inverse broad beam geometry. Pb equivalence was determined using lead sheets as reference material. A substantial variability in photon transmission across garments was found. Differences between lead composite and nonlead garments were not statistically significant. Depending on tube voltage, between 9 and 12 out of 30 garments had a lower Pb equivalence than the indicated value. This work shows that lead equivalence as indicated on a garment's label may overestimate its protective performance. Depending on the application a more thorough verification of the effectiveness of protective garments at the desired kVp is warranted.

MULTICENTRE COMPARISON OF PATIENT AND DETECTOR DOSE FOR X-RAY-GUIDED EMBOLISATIONS OF ARTERIOVENOUS MALFORMATIONS IN THE BRAIN.

Dosimetric benchmarking at four hospitals was performed to investigate incident entrance dose and dose rate on a phantom, and entrance detector dose and dose rate for protocols that are used in routine clinical practice for complex neuroradiological treatment of arteriovenous malformations (AVMs). Measurements were performed with a head phantom that simulates the attenuation and scattering of the human head for the lateral and posteroanterior (PA) views. For fluoroscopy, the measured incident entrance dose rate and entrance detector dose rate were in the range of 44-172 and 0.3-1.3 µGy s(-1), respectively. The pulse rate in fluoroscopy varied between 6.3 and 15 frames per second (fps). For digital subtraction angiography (DSA), incident entrance dose per frame and entrance detector dose per frame were in the range of 744-2800 and 2.6-8.1 µGy/frame, respectively. Optimisation of acquisition parameters such as pulse rate in fluoroscopy, dose per frame in DSA, beam filtration and tube voltage may further improve imaging protocols and lower the patient dose in very complex X-ray-guided embolisations of AVMs in the brain. However, differences in these acquisition parameters observed in this study were relatively small, suggesting that a relatively high degree of optimisation has already been achieved.

MULTICENTRE COMPARISON OF IMAGE QUALITY FOR LOW-CONTRAST OBJECTS AND MICROCATHETER TIPS IN X-RAY-GUIDED TREATMENT OF ARTERIOVENOUS MALFORMATION IN THE BRAIN.

The treatment of brain arteriovenous malformations (AVMs) can be performed as a minimally invasive X-ray-guided procedure using a microcatheter for navigation to reach the target site. The performance of the interventional vascular surgery devices used for AVM was compared in four hospitals. The relation between image quality and the entrance surface air kerma (ESAK) was assessed for the default protocols for digital subtraction angiography (DSA) and fluoroscopy. A custom phantom, built with PMMA and aluminium plates was used to mimic the attenuation properties of the patient head. Image quality was assessed using low-contrast objects and catheters embedded in two phantoms. Differences were found in the ESAK values, especially for the fluoroscopy, whereas for DSA, the ESAK values were similar. The differences in image quality can be related to acquisition parameters, such as kV and filtration, and post-processing. The proposed method can be used to optimise the existing AVM protocols.

General ion recombination for ionization chambers used under irradiation conditions relevant for diagnostic radiology.

General ion recombination has been studied under irradiation conditions relevant for diagnostic radiology and with four different ionization chambers. When the exposure time is appreciably shorter than the ion transit time, the exposure can be designated as pulsed irradiation. On the contrary, for relatively long irradiation times, the term continuous irradiation can be applied. Recombination was estimated by measuring the collected charge at various collecting potentials of the ionization chamber. This is a well-known method in radiotherapy, but unfortunately it cannot be used in diagnostic radiology with typical exposure meters, since they do not offer the option of varying the collecting potential. For exposures with diagnostic x-ray units, an alternative approach is to vary the exposure or exposure rate over a wide range at a constant collecting potential. Experimental and theoretical estimates of ion recombination did not yield similar values. This might be due to several causes, such as differences between the actual and the nominal dimensions and volumes of the ionization chambers, due to errors and uncertainties in the physical parameters used in the theoretical models or due to deviations of the shape of the ionization chambers from the perfect cylindrical or parallel plate geometry. For better accuracy, corrections for recombination losses should therefore be based on experimental verification rather than on theoretical models.

Calculation of computed tomography dose index to effective dose conversion factors based on measurement of the dose profile along the fan shaped beam.

The variation in computed tomography dose index (CTDI) to effective dose conversion factors between different types of CT scanner is large (i.e. a factor of about 2 due to differences in beam shaping filters). Consequently, scanner specific conversion factors have to be applied. For some types of scanner, however, detailed information on the construction of beam shaping filters is not provided by the manufacturers. It is of interest to investigate the use of measured dose profiles for the calculation of conversion factors. Based upon measured dose profiles, two appropriate photon spectra selected on the basis of measured half value layers, gender specific adult phantoms Adam and Eva, and the Monte Carlo neutron and photon radiation transport code (MCNP), organ and effective dose conversion factors are calculated. To validate the method, a comparison is made between results for measured and calculated beam profiles for a Philips Tomoscan 350. The results in terms of effective dose per slice per unit of CTDI are compared with published data. Relative difference in conversion factors per slice averaged over all slices used for the calculations is 13 +/- 4% between the two spectra, 10.2 +/- 0.2% between measured and calculated beam profiles and 50 +/- 191% between the phantoms of different gender. The relative difference between the averaged results for the Adam and Eva phantoms and published results for a hermaphrodite phantom is on average equal to or less than 15 +/- 13%, depending on the spectrum and beam profile used, although larger differences can occur for specific slices. It is concluded that CTDI to effective dose conversion factors can be derived on the basis of measured beam profiles.

Comparison of two methods for assessing patient dose from computed tomography.

Radiation exposure of the patient during routine computed tomography (CT) examinations is known to be relatively high. In this study organ doses were determined using two methods and these served as a basis to calculate the effective dose. Thermoluminescence dosemeters (TLDs) were used to measure organ doses in an anthropomorphic Rando Alderson phantom. In addition organ doses were obtained from measurement of the computed tomography dose index (CTDI) and the application of published organ dose conversion factors. Effective dose values obtained with the Rando phantom for CT head examinations are about 1-2 mSv. For CT examinations of thorax and abdomen the estimation of effective doses with the Rando phantom yielded values of 18 and 24 mSv respectively. Effective doses determined from CTDI values were similar for CT head examinations (1-2 mSv) but were smaller for the CT thorax scan (11-15 mSv) and the CT abdomen scan (15-20 mSv). In this study effective dose values are relatively high compared with the results of other investigators who indicate effective doses and effective dose equivalents of 7-9 mSv for CT of the thorax and of 4-16 mSv for CT of the abdomen. Discrepancies between our results and those from other studies could be attributed to differences in the selected CT protocols and to differences in the phantoms employed. Measurements in an anthropomorphic phantom were laborious and time-consuming. Assessment of organ doses from CTDI values and organ dose conversion factors will therefore be the preferable method for future dose intercomparisons at different locations in The Netherlands. It should be realized, however, that this method tends to yield up to 40% lower effective dose values compared with the assessment of effective dose with a Rando phantom.

Survey of CT techniques and absorbed dose in various Dutch hospitals.

The purpose of this study was to make an inventory of the radiation dose from CT in the Netherlands and to relate the dose to the way the examination was performed. Details were obtained from approximately 3000 CT examinations carried out in 18 hospitals (22 CT scanners). Effective dose was calculated for each examination using CTDI-to-effective dose conversion factors. For most scanners, the conversion factors were available from the literature, for some they had to be derived with a computer model using a Monte Carlo algorithm. The data on effective dose, examination parameters and patient population are presented on a per hospital basis. Mean effective doses from brain CT were 0.8-5 mSv, from lumbar spine CT 2-12 mSv, from chest CT 6-18 mSv and from abdominal CT 6-24 mSv. The general indications for the various CT examinations were as follows: for the brain ischaemia and malignancy, for the lumbar spine disc herniation and for the chest and abdomen a known malignancy. This explains the relatively advanced age of the patients. In many hospitals intravenous contrast is used less than is recommended in current literature.

Patient and staff radiation dose in fluoroscopy-guided TIPS procedures and dose reduction, using dedicated fluoroscopy exposure settings.

Fluoroscopy guided interventions, such as transjugular intrahepatic portosystemic shunt (TIPS) procedures, can results in relatively high radiation doses to patients and staff. The purpose of this study was to evaluate the possible benefit of dedicated fluoroscopy exposure factors in the reduction of doses. Doses to patients and staff were measured during fluoroscopy-guided TIPS procedures in two Dutch university hospitals. Patient doses were calculated from dose-area product (DAP) measurements, entrance beam dimensions and DAP conversion factors. Staff doses were measured outside lead aprons using electronic personal dosemeters. Average patient entrance skin dose (ESD) rate during fluoroscopy was 49 mGy min-1 (13 cases, average fluoroscopy duration 32 min) in one hospital, and 6 mGy min-1 (10 cases, average fluoroscopy duration 50 min) in the other. Estimated staff effective dose per procedure was 28 microSv average in the first hospital compared with 4 microSv average in the other. The use of dedicated fluoroscopy exposure factors, with a relatively high tube voltage and lower tube current resulted in a significant dose reduction for patient and staff in this type of radiological intervention.

Survey of posteroanterior chest radiography in The Netherlands: patient dose and image quality.

Council Directive 97/43/Euratom (Medical Exposure Directive) states that member States of the European Union shall promote the establishment and use of diagnostic reference levels for radio-diagnostic examinations. Dose surveys can form the basis for the establishment of diagnostic reference levels. In view of the implementation of the Medical Exposure Directive in the Netherlands, a survey of dose and image quality has been performed for posteroanterior (PA) chest radiography in 2001. In this survey, 25 participants were selected from a list of 175 Dutch hospitals, whereas in a previous PA chest survey (about 10 years ago) participation was voluntary and participants came predominantly from the south-western part of the Netherlands. For conventional screen-film PA chest radiography, the present results for patient dose and image quality are quite similar to those results from the previous survey. The fraction of conventional X-ray systems utilizing lung compensation filters has remained approximately the same. For dedicated digital chest radiography systems, image quality is better than for conventional systems, but doses vary and can assume relatively high values. The results indicate that there are still possibilities for dose reduction, without loss of image quality. The 75 percentile value of the entrance surface dose distribution is approximately 0.13 mGy.

High prevalence of mannose-binding lectin (MBL) deficiency in premature neonates.

Mannose-binding lectin (MBL) is a component of innate immunity and thus particularly important in neonates in whom adaptive immunity is not yet completely developed. Promoter polymorphisms and structural exon-1 mutations in the MBL2 gene cause reduced or deficient MBL plasma concentrations. The aim of our study was to determine the prevalence of MBL deficiency in neonates admitted to the neonatal intensive care unit (NICU). Eighty-five NICU patients (69 premature) were included in the study. We measured MBL concentrations in umbilical cord and neonatal blood within 24 h after birth by ELISA technique. MBL2 genotypes (n = 67) were determined by Taqman analysis. MBL concentrations were measured longitudinally during three weeks in 26 premature neonates. The association between pre- and intra-partum clinical data and MBL concentrations was investigated. At birth, 29 (42%) premature and six (38%) term neonates had MBL plasma concentrations < or = 0.7 microg/ml which was regarded as deficient. Twenty-one (38%) premature and four (36%) term neonates had variant MBL2 haplotypes, corresponding to exon-1 mutations and the LXPA haplotype. MBL concentrations increased over time in neonates with wild-type MBL2 haplotypes, but not in neonates with variant haplotypes. Low MBL plasma concentrations were related to lower gestational age and variant MBL2 haplotypes. Umbilical cord and neonatal MBL plasma concentrations appeared to be similar. In conclusion, almost half of our NICU patients, especially the premature ones, were MBL-deficient at birth. These infants may be at increased risk of neonatal infections. MBL concentration can reliably be measured in umbilical cord blood and it is positively correlated with gestational and postnatal age.

Cardiac subluxation in traumatic rupture of diaphragm and pericardium.

A patient is described with a traumatic rupture of diaphragm and pericardium which caused intermittent cardiac subluxation. Aspects of diagnosis and surgical treatment are discussed. A survey of the literature is given.

AMBER and conventional chest radiography: comparison of radiation dose and image quality.

The authors compared the radiation dose to the patient and the image quality in advanced multiple-beam equalization radiography (AMBER) with those in conventional chest radiography. Organ doses were estimated for an anthropomorphic phantom from measurements with thermoluminescence dosimeters. These measurements were supplemented with area-air kerma products obtained during chest examinations of 223 patients. Image quality was determined by means of a contrast-detail image evaluation test. An improvement in image quality in regions of high absorption and an increased dose to the patient were found for the AMBER technique compared with the conventional technique. However, for both techniques, the radiation exposure was relatively low compared with other reported values of patient dose during chest radiography. The estimated effective dose for an average-size patient during chest radiography with posteroanterior and lateral projections is 0.085 mSv for the conventional and 0.14 mSv for the AMBER technique.