Cécile R. L. P. N. Jeukens

Efficacy of Radiation Safety Glasses in Interventional Radiology

PurposeThis study was designed to evaluate the reduction of the eye lens dose when wearing protective eyewear in interventional radiology and to identify conditions that optimize the efficacy of radiation safety glasses.MethodsThe dose reduction provided by different models of radiation safety glasses was measured on an anthropomorphic phantom head. The influence of the orientation of the phantom head on the dose reduction was studied in detail. The dose reduction in interventional radiological practice was assessed by dose measurements on radiologists wearing either leaded or no glasses or using a ceiling suspended screen.ResultsThe different models of radiation safety glasses provided a dose reduction in the range of a factor of 7.9–10.0 for frontal exposure of the phantom. The dose reduction was strongly reduced when the head is turned to the side relative to the irradiated volume. The eye closest to the tube was better protected due to side shielding and eyewear curvature. In clinical practice, the mean dose reduction was a factor of 2.1. Using a ceiling suspended lead glass shield resulted in a mean dose reduction of a factor of 5.7.ConclusionsThe efficacy of radiation protection glasses depends on the orientation of the operator’s head relative to the irradiated volume. Glasses can offer good protection to the eye under clinically relevant conditions. However, the performance in clinical practice in our study was lower than expected. This is likely related to nonoptimized room geometry and training of the staff as well as measurement methodology.

Radiation Exposure of Contrast-Enhanced Spectral Mammography Compared With Full-Field Digital Mammography

ObjectivesContrast-enhanced spectral mammography (CESM) shows promising initial results but comes at the cost of increased dose as compared with full-field digital mammography (FFDM). We aimed to quantitatively assess the dose increase of CESM in comparison with FFDM. Materials and MethodsRadiation exposure–related data (such as kilovoltage, compressed breast thickness, glandularity, entrance skin air kerma (ESAK), and average glandular dose (AGD) were retrieved for 47 CESM and 715 FFDM patients. All examinations were performed on 1 mammography unit. Radiation dose values reported by the unit were validated by phantom measurements. Descriptive statistics of the patient data were generated using a statistical software package. ResultsDose values reported by the mammography unit were in good qualitative agreement with those of phantom measurements. Mean ESAK was 10.5 mGy for a CESM exposure and 7.46 mGy for an FFDM exposure. Mean AGD for a CESM exposure was 2.80 mGy and 1.55 mGy for an FFDM exposure. ConclusionsCompared with our institutional FFDM, the AGD of a single CESM exposure is increased by 1.25 mGy (+81%), whereas ESAK is increased by 3.07 mGy (+41%). Dose values of both techniques meet the recommendations for maximum dose in mammography.

Leukemia and brain tumors among children after radiation exposure from CT scans: design and methodological opportunities of the Dutch Pediatric CT Study

Computed tomography (CT) scans are indispensable in modern medicine; however, the spectacular rise in global use coupled with relatively high doses of ionizing radiation per examination have raised radiation protection concerns. Children are of particular concern because they are more sensitive to radiation-induced cancer compared with adults and have a long lifespan to express harmful effects which may offset clinical benefits of performing a scan. This paper describes the design and methodology of a nationwide study, the Dutch Pediatric CT Study, regarding risk of leukemia and brain tumors in children after radiation exposure from CT scans. It is a retrospective record-linkage cohort study with an expected number of 100,000 children who received at least one electronically archived CT scan covering the calendar period since the introduction of digital archiving until 2012. Information on all archived CT scans of these children will be obtained, including date of examination, scanned body part and radiologist’s report, as well as the machine settings required for organ dose estimation. We will obtain cancer incidence by record linkage with external databases. In this article, we describe several approaches to the collection of data on archived CT scans, the estimation of radiation doses and the assessment of confounding. The proposed approaches provide useful strategies for data collection and confounder assessment for general retrospective record-linkage studies, particular those using hospital databases on radiological procedures for the assessment of exposure to ionizing or non-ionizing radiation.

Hippocampal MRI Volumetry at 3 Tesla: Reliability and Practical Guidance

Objectives:Although volumetry of the hippocampus is considered to be an established technique, protocols reported in literature are not described in great detail. This article provides a complete and detailed protocol for hippocampal volumetry applicable to T1-weighted magnetic resonance (MR) images acquired at 3 Tesla, which has become the standard for structural brain research. Materials and Methods:The protocol encompasses T1-weighted image acquisition at 3 Tesla, anatomic guidelines for manual hippocampus delineation, requirements of delineation software, reliability measures, and criteria to assess and ensure sufficient reliability. Moreover, the validity of the correction for total intracranial volume size was critically assessed. The protocol was applied by 2 readers to the MR images of 36 patients with cryptogenic localization-related epilepsy, 4 patients with unilateral hippocampal sclerosis, and 20 healthy control subjects. Results:The uncorrected hippocampal volumes were 2923 ± 500 mm3 (mean ± SD) (left) and 3120 ± 416 mm3 (right) for the patient group and 3185 ± 411 mm3 (left) and 3302 ± 411 mm3 (right) for the healthy control group. The volume of the 4 pathologic hippocampi of the patients with unilateral hippocampal sclerosis was 2980 ± 422 mm3. The inter-reader reliability values were determined: intraclass-correlation-coefficient (ICC) = 0.87 (left) and 0.86 (right), percentage volume difference (VD) = 7.0 ± 4.7% (left) and 6.0 ± 3.8% (right), and overlap ratio (OR) = 0.82 ± 0.04 (left) and 0.82 ± 0.03 (right). The positive Pearson correlation between hippocampal volume and total intracranial volume was found to be low: r = 0.48 (P = 0.03, left) and r = 0.62 (P = 0.004, right) and did not significantly reduce the volumetric variances, showing the limited benefit of the brain size correction. Conclusions:A protocol was described to determine hippocampal volumes based on 3 Tesla MR images with high inter-reader reliability. Although the reliability of hippocampal volumetry at 3 Tesla was similar to the literature values obtained at 1.5 Tesla, hippocampal border definition is argued to be more confident and easier because of the improved signal-to-noise characteristics.

Memory processes and prefrontal network dysfunction in cryptogenic epilepsy

Purpose:  Impaired memory performance is the most frequently reported cognitive problem in patients with chronic epilepsy. To examine memory deficits many studies have focused on the role of the mesiotemporal lobe, mostly with hippocampal abnormalities. However, the role of the prefrontal brain remains unresolved. To investigate the neuronal correlates of working memory dysfunction in patients without structural lesions, a combined study of neurocognitive assessment, hippocampal and cerebral volumetry, and functional magnetic resonance imaging of temporal and frontal memory networks was performed.

Dynamic Contrast-enhanced CT for Prostate Cancer: Relationship between Image Noise, Voxel Size, and Repeatability

PURPOSE To evaluate the relationship between image noise, voxel size, and voxel-wise repeatability of a dynamic contrast agent-enhanced (DCE) computed tomographic (CT) examination for prostate cancer. MATERIALS AND METHODS This prospective study was approved by the local research ethics committee, and all patients gave written informed consent. Twenty-nine patients (mean age, 69.1 years; range, 56-80 years) with biopsy-proved prostate cancer underwent two DCE CT examinations within 1 week prior to radiation therapy. Parameter maps of transfer constant (K(trans)), the fraction of blood plasma (v(p)), the fraction of extravascular extracellular space (v(e)), and the flux rate constant between the extravascular extracellular space and plasma (k(ep)) were calculated at 15 different image resolutions, with kernel sizes ranging from 0.002 to 2.57 cm(3). Statistical analysis to quantify the voxel-wise repeatability was performed by using a Bland-Altman analysis on all tracer kinetic model parameter maps of each patient. From this analysis, the within-voxel standard deviation (wSD) was calculated as a function of spatial resolution. RESULTS A kernel size in the range of 0.1-0.3 cm(3) yields reliable information. At 0.15 cm(3), the median wSDs of K(trans), k(ep), v(p), and v(e) are 0.047 min(-1), 0.144 min(-1), 0.011, and 0.104, respectively. With increasing kernel size, these values reach stable levels of approximately 0.02 min(-1), 0.05 min(-1), 0.005, and 0.05, respectively. CONCLUSION There is a high voxel-wise repeatability of the DCE CT imaging technique for prostate cancer for kernel sizes as small as 0.1 cm(3). With the relationship between kernel size, image noise and voxel-wise repeatability, it becomes possible to estimate for alternative DCE CT protocols (eg, those with a reduced radiation dose) at what kernel size a sufficient repeatability can be obtained.

Blood–brain barrier leakage is more widespread in patients with cerebral small vessel disease

Objective: As blood–brain barrier (BBB) dysfunction may occur in normal aging but may also play a pivotal role in the pathophysiology of cerebral small vessel disease (cSVD), we used dynamic contrast-enhanced (DCE)–MRI to quantify the rate and the spatial extent of BBB leakage in patients with cSVD and age- and sex-matched controls to discern cSVD-related BBB leakage from aging-related leakage. Methods: We performed structural brain MRI and DCE-MRI in 80 patients with clinically overt cSVD and 40 age- and sex-matched controls. Using the Patlak pharmacokinetic model, we calculated the leakage rate. The mean leakage rate and relative leakage volume were calculated using noise-corrected histogram analysis. Leakage rate and leakage volume were compared between patients with cSVD and controls for the normal-appearing white matter (NAWM), white matter hyperintensities (WMH), cortical gray matter (CGM), and deep gray matter. Results: Multivariable linear regression analyses adjusting for age, sex, and cardiovascular risk factors showed that the leakage volume of the NAWM, WMH, and CGM was significantly larger in patients with cSVD compared with controls. No significant difference was found for leakage rate in any of the tissue regions. Conclusion: We demonstrated a larger tissue volume with subtle BBB leakage in patients with cSVD than in controls. This was shown in the NAWM, WMH, and CGM, supporting the generalized nature of cSVD.

Evaluation of low-energy contrast-enhanced spectral mammography images by comparing them to full-field digital mammography using EUREF image quality criteria

AbstractObjectiveContrast-enhanced spectral mammography (CESM) examination results in a low-energy (LE) and contrast-enhanced image. The LE appears similar to a full-field digital mammogram (FFDM). Our aim was to evaluate LE CESM image quality by comparing it to FFDM using criteria defined by the European Reference Organization for Quality Assured Breast Screening and Diagnostic Services (EUREF).MethodsA total of 147 cases with both FFDM and LE images were independently scored by two experienced radiologists using these (20) EUREF criteria. Contrast detail measurements were performed using a dedicated phantom. Differences in image quality scores, average glandular dose, and contrast detail measurements between LE and FFDM were tested for statistical significance.ResultsNo significant differences in image quality scores were observed between LE and FFDM images for 17 out of 20 criteria. LE scored significantly lower on one criterion regarding the sharpness of the pectoral muscle (p < 0.001), and significantly better on two criteria on the visualization of micro-calcifications (p = 0.02 and p = 0.034). Dose and contrast detail measurements did not reveal any physical explanation for these observed differences.ConclusionsLow-energy CESM images are non-inferior to FFDM images. From this perspective FFDM can be omitted in patients with an indication for CESM.Key Points• Low-energy CESM images are non-inferior to FFDM images. • Micro-calcifications are significantly more visible on LE CESM than on FFDM. • There is no physical explanation for this improved visibility of micro-calcifications. • There is no need for an extra FFDM when CESM is indicated.

Subtle blood-brain barrier leakage rate and spatial extent: considerations for dynamic contrast-enhanced MRI

Purpose: Dynamic contrast‐enhanced (DCE) MRI can be used to measure blood‐brain barrier (BBB) leakage. In neurodegenerative disorders such as small vessel disease and dementia, the leakage can be very subtle and the corresponding signal can be rather noisy. For these reasons, an optimized DCE‐MRI measurement and study design is required. To this end, a new measure indicative of the spatial extent of leakage is introduced and the effects of scan time and sample size are explored. Methods: Dual‐time resolution DCE‐MRI was performed in 16 patients with early Alzheimers disease (AD) and 17 healthy controls. The leakage rate (Ki) and volume fraction of detectable leaking tissue (vL) to quantify the spatial extent of BBB leakage were calculated in cortical gray matter and white matter using noise‐corrected histogram analysis of leakage maps. Computer simulations utilizing realistic Ki histograms, mimicking the strong effect of noise and variation in Ki values, were performed to understand the influence of scan time on the estimated leakage. Results: The mean Ki was very low (order of 10−4 min−1) and highly influenced by noise, causing the Ki to be increasingly overestimated at shorter scan times. In the white matter, the Ki was not different between patients with early AD and controls, but was higher in the cortex for patients, reaching significance after 14.5 min of scan time. To detect group differences, vL proved more suitable, showing significantly higher values for patients compared with controls in the cortex after 8 minutes of scan time, and in white matter after 15.5 min. Conclusions: Several ways to improve the sensitivity of a DCE‐MRI experiment to subtle BBB leakage were presented. We have provided vL as an attractive and potentially more time‐efficient alternative to detect group differences in subtle and widespread blood‐brain barrier leakage compared with leakage rate Ki. Recommendations on group size and scan time are made based on statistical power calculations to aid future research.

Average glandular dose in digital mammography and digital breast tomosynthesis: comparison of phantom and patient data

For the evaluation of the average glandular dose (AGD) in digital mammography (DM) and digital breast tomosynthesis (DBT) phantoms simulating standard model breasts are used. These phantoms consist of slabs of polymethyl methacrylate (PMMA) or a combination of PMMA and polyethylene (PE). In the last decades the automatic exposure control (AEC) increased in complexity and became more sensitive to (local) differences in breast composition. The question is how well the AGD estimated using these simple dosimetry phantoms agrees with the average patient AGD. In this study the AGDs for both dosimetry phantoms and for patients have been evaluated for 5 different x-ray systems in DM and DBT modes. It was found that the ratios between patient and phantom AGD did not differ considerably using both dosimetry phantoms. These ratios averaged over all breast thicknesses were 1.14 and 1.15 for the PMMA and PMMA-PE dosimetry phantoms respectively in DM mode and 1.00 and 1.02 in the DBT mode. These ratios were deemed to be sufficiently close to unity to be suitable for dosimetry evaluation in quality control procedures. However care should be taken when comparing systems for DM and DBT since depending on the AEC operation, ratios for particular breast thicknesses may differ substantially (0.83-1.96). Although the predictions of both phantoms are similar we advise the use of PMMA  +  PE slabs for both DM and DBT to harmonize dosimetry protocols and avoid any potential issues with the use of spacers with the PMMA phantoms.