Carlos Ubeda

Radiation dose and image quality for paediatric interventional cardiology

Radiation dose and image quality for paediatric protocols in a biplane x-ray system used for interventional cardiology have been evaluated. Entrance surface air kerma (ESAK) and image quality using a test object and polymethyl methacrylate (PMMA) phantoms have been measured for the typical paediatric patient thicknesses (4-20 cm of PMMA). Images from fluoroscopy (low, medium and high) and cine modes have been archived in digital imaging and communications in medicine (DICOM) format. Signal-to-noise ratio (SNR), figure of merit (FOM), contrast (CO), contrast-to-noise ratio (CNR) and high contrast spatial resolution (HCSR) have been computed from the images. Data on dose transferred to the DICOM header have been used to test the values of the dosimetric display at the interventional reference point. ESAK for fluoroscopy modes ranges from 0.15 to 36.60 microGy/frame when moving from 4 to 20 cm PMMA. For cine, these values range from 2.80 to 161.10 microGy/frame. SNR, FOM, CO, CNR and HCSR are improved for high fluoroscopy and cine modes and maintained roughly constant for the different thicknesses. Cumulative dose at the interventional reference point resulted 25-45% higher than the skin dose for the vertical C-arm (depending of the phantom thickness). ESAK and numerical image quality parameters allow the verification of the proper setting of the x-ray system. Knowing the increases in dose per frame when increasing phantom thicknesses together with the image quality parameters will help cardiologists in the good management of patient dose and allow them to select the best imaging acquisition mode during clinical procedures.

SCATTER AND STAFF DOSE LEVELS IN PAEDIATRIC INTERVENTIONAL CARDIOLOGY: A MULTICENTRE STUDY

Interventional cardiology procedures usually imply high doses to the staff, as paediatric cardiologists need to stay closer to the patient than during adult procedures. Also, biplane systems are used that imply an additional source of staff doses. The objective of this paper is to measure scatter doses in four X-ray systems, using polymethyl methacrylate phantoms with thicknesses ranging from 4 to 16 cm to simulate paediatric patients, for the different acquisition modes. Scatter dose rates measured at the position of cardiologists eyes ranged from 0.8 to 12 mSv h(-1), and about twice the above values at lower extremities, as a linear function of the surface air kerma at the phantom, keeping the irradiated area constant. Therefore, the respective personal dose equivalent for the lens of the eyes may be around 0.5 and 1 mSv throughout the procedure, if additional protection is not used. Simultaneous cine acquisition in biplane systems yielded scatter doses to cardiologists, increased by factors from 5 to 21, compared with a single C-arm acquisition case and depending on geometry. Knowledge of scatter doses for different operation modes, patient thicknesses and the biplane operation should help paediatric cardiologists to adopt conservative attitudes in respect of their occupational radiation risks.

Radiation protection in pediatric interventional cardiology: An IAEA PILOT program in Latin America.

The aim of this work is to present a methodology and some initial results for a pilot program on radiation protection (RP) in pediatric interventional cardiology under the auspices of the International Atomic Energy Agency. The starting point of the program was a workshop involving several pediatric cardiologists leading this specialty in 11 Latin American countries. The workshop included a pilot RP training course and additional sessions during which the objectives of the program and the methodology to collect and process data on patient and staff radiation doses were discussed. Special attention was dedicated to agree on a common quality control (QC) protocol for the x-ray and imaging systems used in the different catheterization laboratories. The preliminary data showed that only 64% of the cardiologists used their personal dosimeters regularly and that only 36% were aware of their personal dose values. The data on pediatric interventional activity were collected from 10 centers from nine different countries. A total of 2,429 procedures (50% diagnostic and 50% therapeutic) were carried out during 2009 in these centers. Patient dose data were available in only a few centers and were not analyzed on a regular basis in any of the catheterization laboratories involved. Plans were developed for a basic QC protocol of the x-ray systems and construction of a Latin American database on pediatric cardiology with patient and staff dose values with the idea in mind of obtaining distributions of these dose values before promoting several optimization strategies.

Pilot program on patient dosimetry in pediatric interventional cardiology in Chile

PURPOSE The aim of this study was to present the results of a pilot program on patient dosimetry carried out in Chile during the last 5 yr, using a biplane x-ray angiography system settled for pediatrics. This research was conducted in Latin America under the auspices of the International Atomic Energy Agency (IAEA) supporting programs on radiological protection (RP) of patients. METHODS Patient age, gender, weight, height, number of cine series, total number of cine frames, fluoroscopy time, and two dosimetric quantities [air kerma-area product (P(ka)) and cumulative dose (CD) at the patient entrance reference point] were recorded for each procedure. RESULTS The study includes 544 patients grouped into four age groups. The distributions by age group were 150 for <1 yr; 203 for 1 to <5 yr; 97 for 5 to <10 yr; and 94 for 10 to <16 yr. Median values of P(ka) and CD for the four age groups were 0.94, 1.46, 2.13, and 5.03 Gy cm(2) and 23.9, 26.8, 33.5, and 51.6 mGy, respectively. No significant statistical differences were found between diagnostic and therapeutic procedures. A moderate correlation (r = 0.64) was seen between P(ka) and patient weight. CONCLUSIONS The dose values reported in this paper were lower than those published in the previous work for the same age groups as a result of the optimization actions carried out by cardiologists and medical physicists with the support of the IAEA. Methodology and results will be used as a starting point for a wider survey in Chile and Latin America with the goal to obtain regional diagnostic reference levels as recently recommended by the International Commission on Radiological Protection for interventional procedures.

Influence of the antiscatter grid on dose and image quality in pediatric interventional cardiology X-ray systems.

To present a methodology and experimental results to assess the influence, in terms of dose and image quality, of the antiscatter grid (AG) in a pediatric cardiology X‐ray system.

Radiation dose and image quality for paediatric interventional cardiology systems. A national survey in Chile

Radiation dose and image quality for paediatric protocols in all five X-ray fluoroscopy systems used for interventional cardiology procedures existing in Chile have been evaluated. Entrance surface air kerma (ESAK) and image quality using a test object (TO) and polymethyl methacrylate (PMMA) phantoms have been measured for the typical paediatric patient thicknesses (4-16 cm of PMMA). Images from fluoroscopy (low (FL), medium and high) and cine (CI) modes have been archived in DICOM format. Signal-to-noise ratio (SNR), figure of merit (FOM) and high-contrast spatial resolution (HCSR) have been computed from the images. The ratio between the maximum and the minimum value of ESAK per frame for a given fluoroscopy mode between the five systems ranges from 2 to 5 and from 14 to 38 for CI mode. SNR, FOM and HCSR showed a great variability for the different acquisition modes (AMs) and PMMA thickness. In the near future, it is urgent to upgrade Chilean legislation on radiation protection to incorporate quality assurance programmes that will allow us to evaluate and optimise the X-ray systems used in medical applications. Increments in doses per frame when increasing phantom thickness and when used CI runs instead of FL runs can be considered by the cardiologist in the good management of patient dose and allow them to select the best imaging AM during clinical procedures.

Patient doses in paediatric interventional cardiology: impact of 3D rotational angiography

The aim of this study was to calculate the contribution of 3D rotational angiography to radiation doses received by paediatric patients in a cardiac catheterisation laboratory. The percentage increase in the median value of air kerma-area product due to cone beam CT was 33 and 16% for diagnostic and therapeutic procedures, respectively. Results are presented separately for five age groups and ten weight groups. Several methods for reducing radiation from 3D rotational angiography are suggested and patient doses are compared with previously published values.

Paediatric interventional cardiology: flat detector versus image intensifier using a test object

Entrance surface air kerma (ESAK) values and image quality parameters were measured and compared for two biplane angiography x-ray systems dedicated to paediatric interventional cardiology, one equipped with image intensifiers (II) and the other one with dynamic flat detectors (FDs). Polymethyl methacrylate phantoms of different thicknesses, ranging from 8 to 16 cm, and a Leeds TOR 18-FG test object were used. The parameters of the image quality evaluated were noise, signal-difference-to-noise ratio (SdNR), high contrast spatial resolution (HCSR) and three figures of merit combining entrance doses and signal-to-noise ratios or HCSR. The comparisons showed a better behaviour of the II-based system in the low contrast region over the whole interval of thicknesses. The FD-based system showed a better performance in HCSR. The FD system evaluated would need around two times more dose than the II system evaluated to reach a given value of SdNR; moreover, a better spatial resolution was measured (and perceived in conventional monitors) for the system equipped with flat detectors. According to the results of this paper, the use of dynamic FD systems does not lead to an automatic reduction in ESAK or to an automatic improvement in image quality by comparison with II systems. Any improvement also depends on the setting of the x-ray systems and it should still be possible to refine these settings for some of the dynamic FDs used in paediatric cardiology.

Impact of the X-ray system setting on patient dose and image quality; a case study with two interventional cardiology systems

This study investigates the influence of the initial X-ray system setting on patient doses and image quality in interventional cardiology procedures. Two dedicated interventional cardiology systems were studied: a system with image intensifier (II) and a flat detector (FD) system. Entrance surface air kerma (ESAK) rates in fluoroscopy and ESAK per frame in the acquisition mode were measured on the surface of a PMMA phantom for the field of views (FOV) of 23 and 17 cm (II system) and 25 and 20 cm (FD system). Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were estimated using DICOM images obtained during the measurements. System performances were compared using a figure of merit combining SNR and ESAK. The influence of system setting on patient doses was investigated analysing the information for air kerma area product (KAP) and cumulative dose (CD) at the patient entrance reference point, for a sample of coronary angiography examinations. ESAK rates in fluoroscopy modes were a factor of 2 higher in the FD system for the similar FOVs, resulting in a factor of 1.9 higher median values of KAP and CD for patients with FD system than for the II system. SNR and CNR for the FD system were better than the equivalent FOVs with II. The resulting FOM was better for the FD system in both FOVs. Potential for optimisation was suggested by adjusting system settings.

Evaluation of patient doses and lens radiation doses to interventional cardiologists in a nationwide survey in Chile.

The objective of this study was to perform a nationwide survey in Chile to determine dose levels to patients and staff in four risk scenarios during cardiac catheterisation procedures. Different phantom thicknesses of polymethyl methacrylate (PMMA) were used to simulate adult patients. Scenario 1: 10-min fluoroscopy and 800 cine frames for 20 cm of PMMA; Scenario 2: 10-min fluoroscopy and 800 cine frames for 28 cm of PMMA; Scenario 3: 30-min fluoroscopy and 2400 cine frames for 20 cm of PMMA; Scenario 4: 30-min fluoroscopy and 2400 cine frames for 28 cm of PMMA. The average values regarding dose-area product and scattered doses at the cardiologist eye lens achieved for the four scenarios were 94, 249, 281, 747 Gy cm(2) and 0.3, 0.8, 0.9 and 2.5 mSv, respectively. Large variations in radiation doses received by both patients and staff for the same type of procedure suggest that optimising procedure protocols and using the most effective types of protective devices may substantially reduce the dose values found here.