Klaus Bacher

Patient-Specific Dose and Radiation Risk Estimation in Pediatric Cardiac Catheterization

Background—Because of the higher radiosensitivity of infants and children compared with adults, there is a need to evaluate the doses delivered to pediatric patients who undergo interventional cardiac procedures. However, knowledge of the effective dose in pediatric interventional cardiology is very limited. Methods and Results—For an accurate risk estimation, a patient-specific Monte Carlo simulation of the effective dose was set up in 60 patients with congenital heart disease who underwent diagnostic (n=28) or therapeutic (n=32) cardiac catheterization procedures. The dose-saving effect of using extra copper filtration in the x-ray beam was also investigated. For diagnostic cardiac catheterizations, a median effective dose of 4.6 mSv was found. Therapeutic procedures resulted in a higher median effective dose of 6.0 mSv because of the prolonged use of fluoroscopy. The overall effect of inserting extra copper filtration into the x-ray beam was a total effective dose reduction of 18% with no detrimental effect on image quality. An excellent correlation between the dose-area product and effective patient dose was found (r=0.95). Hence, dose-area product is suitable for online estimation of the effective dose with good accuracy. With all procedures included, the resulting median lifetime risk for stochastic effects was 0.08%. Conclusions—Because of the high radiation exposure, it is important to monitor patient dose by dose-area product instrumentation and to use additional beam filtration to keep the effective dose as low as possible in view of the sensitivity of the pediatric patients.

γ-H2AX Foci as a Biomarker for Patient X-Ray Exposure in Pediatric Cardiac Catheterization Are We Underestimating Radiation Risks?

Background— A better knowledge of patient x-ray dose and the associated radiation risk in pediatric interventional cardiology is warranted in view of the extensive use of x-rays and the higher radiosensitivity of children. In the present study, &ggr;-H2AX foci were used as a biomarker for radiation-induced effects. Patient-specific dose was assessed and radiation risks were estimated according to the linear-no-threshold model, commonly used in radiation protection, and the &ggr;-H2AX foci data. Methods and Results— In 49 pediatric patients (median age, 0.75 years) with congenital heart disease who underwent cardiac catheterization procedures, blood samples were taken before and shortly after the procedure. &ggr;-H2AX foci were determined in peripheral blood T lymphocytes. In each patient, a net increase in &ggr;-H2AX foci, representing DNA double-strand breaks induced by interventional x-rays, was observed. In addition, a patient-specific Monte Carlo simulation of the procedure was performed, resulting in individual blood, organ, and tissue doses. Plotting of &ggr;-H2AX foci versus blood dose indicated a low-dose hypersensitivity. Median effective doses calculated according to the International Commission on Radiological Protection 60 and 103 publications are 5.6 and 6.4 mSv, respectively. The lifetime-attributable risk of cancer mortality was calculated from the linear-no-threshold model and the &ggr;-H2AX foci data. This resulted in lifetime-attributable risk values of 1 per thousand and 4 per thousand, respectively, for the patient population under study. Conclusions— &ggr;-H2AX foci as a biomarker for DNA damage indicate that radiation risk estimates according to the linear-no-threshold hypothesis are possibly underestimates. Great care should be taken to minimize and optimize patient radiation exposure.

Cone beam computed tomography, a low-dose imaging technique in the postoperative assessment of cochlear implantation.

Background: Cone beam computed tomography (CBCT) has become an extremely useful technique for dentomaxillofacial imaging because it provides clear images of highly contrasted structures. Previous studies evaluating the applicability of this technique in otologic imaging were very encouraging but were only performed in vitro on temporal bone specimens. The intracochlear positioning of the individual electrodes after cochlear implantation by means of CBCT has not yet been shown in vivo. Objective: We describe a protocol for in vivo postoperative imaging of cochlear implants by CBCT. Moreover, the effective dose was measured and compared with the effective dose used on 4- and 16-slice multislice computed tomography (MSCT) by using a RANDO-phantom. Main Outcome Measure: Developing a protocol for in vivo postoperative imaging of cochlear implants by CBCT. Results: CBCT provides high-resolution and almost artifact-free multiplanar reconstruction images allowing assessment of the precise intracochlear position of the electrode and visualization of each of the individual contacts. The calculated effective dose of the used CBCT and MSCT acquisitions is 80 &mgr;sv for the CBCT, 3,600 &mgr;sv for the 16-slice computed tomography, and 4,800 &mgr;sv for the 4-slice computed tomography. Conclusion: These preliminary results suggests that, for in vivo postoperative evaluation of cochlear implants, CBCT can provide at least the same information as conventional radiography, digital radiograph, and MSCT but in a more comfortable and a much more safer way.

A large-scale multicentre study of patient skin doses in interventional cardiology: dose–area product action levels and dose reference levels

For 318 patients in 8 different Belgian hospitals, the entire skin-dose distribution was mapped using a grid of 70 thermoluminescence dosimeters per patient, allowing an accurate determination of the maximum skin dose (MSD). Dose-area product (DAP) values, exposure parameters and geometry, together with procedure, patient and cardiologist characteristics, were also registered. Procedures were divided into two groups: diagnostic procedures (coronary angiography) and therapeutic procedures (dilatation, stent, combined procedures (e.g. coronary angiography + dilatation + stent)). The mean value of the MSD was 0.310 Gy for diagnostic and 0.699 Gy for therapeutic procedures. The most critical projection for receiving the MSD is the LAO90 (left anterior oblique) geometry. In 3% of cases, the MSD exceeded the 2 Gy dose threshold for deterministic effects. Action levels in terms of DAP values as the basis for a strategy for follow-up of patients for deterministic radiation skin effects were derived from measured MSD and cumulative DAP values. Two DAP action levels are proposed. A first DAP action level of 125 Gy cm(2) corresponding to the dose threshold of 2 Gy would imply an optional radiopathological follow-up depending on the cardiologists decision. A second DAP action level of 250 Gy cm(2) corresponding to the 3 Gy skin dose would imply a systematic follow-up. Dose reference levels - 71.3 Gy cm(2) for diagnostic and 106.0 Gy cm(2) for therapeutic procedures - were derived from the 75 percentile of the DAP distributions. As a conclusion, we propose that total DAP is registered in patients record file, as it can serve to improve the follow-up of patients for radiation-induced skin injuries.

Digital Tomosynthesis in the Detection of Urolithiasis: Diagnostic Performance and Dosimetry Compared With Digital Radiography With MDCT as the Reference Standard

OBJECTIVE The purpose of this study was to evaluate the diagnostic performance of digital tomosynthesis in comparison with digital radiography in the detection of urinary stones with MDCT as the reference standard. SUBJECTS AND METHODS Fifty consecutively enrolled patients (32 men, 18 women; mean age, 51.5 years; range, 19-83 years) referred for unenhanced MDCT of the abdomen with suspicion of urinary stones also underwent digital tomosynthesis and digital radiography (anteroposterior and bladder inlet views). Images from all examinations were randomly read by three blinded radiologists. The mean effective doses for digital tomosynthesis, digital radiography, and low- and high-dose MDCT were measured on a male phantom. Free-response receiver operating characteristics and receiver operating characteristics analyses were used to compare the diagnostic performance of digital radiography with that of digital tomosynthesis. RESULTS Both types of analysis showed significantly better performance of tomosynthesis over digital radiography for all urinary stones (p < 0.05). No such improvement was found for ureteral stones. The gain in sensitivity with tomosynthesis was largest for stones between 2 and 5 mm in diameter. The mean effective dose was 0.5 mSv for digital radiography, 0.85 mSv for tomosynthesis, 2.5 mSv for low-dose MDCT, and 12.6 mSv for high-dose MDCT. CONCLUSION Use of digital tomosynthesis of the abdomen results in improved detection of urinary stones in general over digital radiography with only a slight increase in effective dose. Use of tomosynthesis, however, was not associated with major improvement in the diagnosis of ureteral stones. The technique has potential as an alternative imaging technique in the detection and follow-up of urinary stones.

Correlation of Contrast-Detail Analysis and Clinical Image Quality Assessment in Chest Radiography with a Human Cadaver Study

PURPOSE To determine the correlation between the clinical and physical image quality of chest images by using cadavers embalmed with the Thiel technique and a contrast-detail phantom. MATERIALS AND METHODS The use of human cadavers fulfilled the requirements of the institutional ethics committee. Clinical image quality was assessed by using three human cadavers embalmed with the Thiel technique, which results in excellent preservation of the flexibility and plasticity of organs and tissues. As a result, lungs can be inflated during image acquisition to simulate the pulmonary anatomy seen on a chest radiograph. Both contrast-detail phantom images and chest images of the Thiel-embalmed bodies were acquired with an amorphous silicon flat-panel detector. Tube voltage (70, 81, 90, 100, 113, 125 kVp), copper filtration (0.1, 0.2, 0.3 mm Cu), and exposure settings (200, 280, 400, 560, 800 speed class) were altered to simulate different quality levels. Four experienced radiologists assessed the image quality by using a visual grading analysis (VGA) technique based on European Quality Criteria for Chest Radiology. The phantom images were scored manually and automatically with use of dedicated software, both resulting in an inverse image quality figure (IQF). Spearman rank correlations between inverse IQFs and VGA scores were calculated. RESULTS A statistically significant correlation (r = 0.80, P < .01) was observed between the VGA scores and the manually obtained inverse IQFs. Comparison of the VGA scores and the automated evaluated phantom images showed an even better correlation (r = 0.92, P < .001). CONCLUSION The results support the value of contrast-detail phantom analysis for evaluating clinical image quality in chest radiography.

Biodistribution and dosimetry study of 123I-rh-annexin V in mice and humans.

Summary This study reports on the optimization of the labelling procedure of clinical grade 123I‐rh‐annexin V and on the investigation of the biodistribution and dosimetry of 123I‐rh‐annexin V, a tracer proposed for the study of apoptosis in mice and humans. Research grade 123I‐rh‐annexin V was prepared as described previously, whereas clinical grade 123I‐rh‐annexin V was prepared according to a modified IodoGen method. NMRI mice, 3–4 weeks of age, received research grade 123I‐rh‐annexin V (74.0 + 3.7 kBq/mouse) by intravenous (i.v.) injection and killed at preset time points. Afterwards, the collected organs, blood, urine and faeces were counted for radioactivity and determined as %ID/g tissue or %ID over time. Secondly, six volunteers with normal liver and kidney function underwent whole‐body scans up to 21 h after i.v. injection of clinical grade 123I‐rh‐annexin V (345 ±38 MBq). Time‐activity curves were generated for the organs of interest, e.g., thyroid, heart, liver, kidneys and whole body, by fitting the organ specific geometric mean counts, obtained from region of interest analysis of acquired images in humans. The MIRD formulation was applied to calculate the absorbed radiation doses for various organs. Clinical grade 123I‐rh‐annexin V was obtained in radiochemical yields of 87.0 + 6.5% and radiochemical purities >98%. In mice, research grade 123I‐rh‐annexin V accumulated primarily in liver, kidney, stomach and lung tissue, limiting its usefulness for imaging of ongoing apoptosis in the abdominal and thoracic region. Clearance was predominantly urinary. In humans, acquired images with the clinical grade radioligand showed low lung uptake, resulting in good imaging conditions for the thoracic region. On the other hand, delayed imaging of the abdominal region was impeded due to extensive bowel activity. The highest absorbed doses were received by the thyroid, the kidneys, the heart wall, the liver and bone surfaces. The average effective dose of 123I‐rh‐annexin V was estimated to be 0.02 mSv·MBq‐1. The amount of 123I‐rh‐annexin V required for in vivo imaging, results in an acceptable effective dose to the patient.

Dose-length product of scanners correlates with DNA damage in patients undergoing contrast CT

OBJECTIVES Computed tomography (CT) exams contribute for a large part to the populations radiation burden. This study addresses the question if dose settings of scanners expressed by dose-length product (DLP) are correlated with directly measurable biological effects in patients. METHODS DLP, blood dose, effective dose and DNA damage were analyzed for patients undergoing a thoracic or abdominal contrast CT scan on two CT scanners with different dose settings. The DNA damage was assessed by scoring γ-H2AX foci representing DNA double-strand breaks (DSBs) in patients lymphocytes. Blood dose was calculated using the ImPACT software. RESULTS The CT system operating at higher dose settings represented by higher DLP values, resulted in a significantly higher number of radiation-induced γ-H2AX foci in patients lymphocytes (DLP: 2.1 times higher; γ-H2AX foci: 2.3 times higher; p<0.05). Plotting γ-H2AX foci versus blood dose showed a systematic increase of DNA damage with dose. In vitro experiments ruled out a possible X-ray enhancement of DNA damage effect by contrast agent. CONCLUSIONS Present study demonstrates that optimization of DLP setting of scanners results in a reduction of X-ray effects in patients.

Image Quality and Radiation Dose on Digital Chest Imaging: Comparison of Amorphous Silicon and Amorphous Selenium Flat-Panel Systems

OBJECTIVE The aim of this study was to compare the image quality and radiation dose in chest imaging using an amorphous silicon flat-panel detector system and an amorphous selenium flat-panel detector system. In addition, the low-contrast performance of both systems with standard and low radiation doses was compared. MATERIALS AND METHODS In two groups of 100 patients each, digital chest radiographs were acquired with either an amorphous silicon or an amorphous selenium flat-panel system. The effective dose of the examination was measured using thermoluminescent dosimeters placed in an anthropomorphic Rando phantom. The image quality of the digital chest radiographs was assessed by five experienced radiologists using the European Guidelines on Quality Criteria for Diagnostic Radiographic Images. In addition, a contrast-detail phantom study was set up to assess the low-contrast performance of both systems at different radiation dose levels. Differences between the two groups were tested for significance using the two-tailed Mann-Whitney test. RESULTS The amorphous silicon flat-panel system allowed an important and significant reduction in effective dose in comparison with the amorphous selenium flat-panel system (p < 0.0001) for both the posteroanterior and lateral views. In addition, clinical image quality analysis showed that the dose reduction was not detrimental to image quality. Compared with the amorphous selenium flat-panel detector system, the amorphous silicon flat-panel detector system performed significantly better in the low-contrast phantom study, with phantom entrance dose values of up to 135 muGy. CONCLUSION Chest radiographs can be acquired with a significantly lower patient radiation dose using an amorphous silicon flat-panel system than using an amorphous selenium flat-panel system, thereby producing images that are equal or even superior in quality to those of the amorphous selenium flat-panel detector system.

Novel X‐ray imaging technology enables significant patient dose reduction in interventional cardiology while maintaining diagnostic image quality

The purpose of this study was to quantify the reduction in patient radiation dose during coronary angiography (CA) by a new X‐ray technology, and to assess its impact on diagnostic image quality.