CONE BEAM CT IN DENTAL IMPLANT PLANNING: HOW CLOSE ARE PATIENT DOSIMETRY RESULTS WITH DATA FROM PHANTOM STUDIES FOUND IN LITERATURE?

Advantages of Cone Beam Computed Tomography (CBCT) include high-quality 3D imaging and reduced radiation exposure with relatively low cost. In this study, patient radiation exposure in CBCT implant planning dentistry was measured in terms of Kerma Area Product (KAP). Data were obtained from 217 CBCT scans on 168 individuals using a CS9300 Carestream system. Scans were made using 80-90 kVp, 4-5 mA, 8 and 13.3 s exposure time (depending on voxel size) and a fixed field of view (FOV) of 10 × 10 cm2 (medium). Mean KAP was estimated using two voxel sizes 180 × 180 × 180 µm3 and 200 × 200 × 200 µm3 and found to be 399 and 314 mGycm2, respectively. Corresponding KAP values found in literature ranged between 210 and 2140 mGycm2. Mean E was estimated using conversion coefficient factors found in literature, according to FOV size and tube voltage value and found to range between 24 and 161 µSv.

Towards the definition of Institutional diagnostic reference levels in paediatric interventional cardiology procedures in Greece.

This study aimed to evaluate paediatric radiation doses in a dedicated cardiology hospital, with the objective of characterising patterns in dose variation. The ultimate purpose was to define Local (Institutional) Diagnostic Reference Levels (LDRLs) for different types of paediatric cardiac interventional procedures (IC), according to patient age. From a total of 710 cases performed during three consecutive years, by operators with more than 15 years of experience, the age was noted in only 477 IC procedures. The median values obtained for Fluoroscopy Time (FT), Number of Frames (N) and Kerma Area Product (PKA) by age range were 5.8 min, 1322 and 2.0 Gy.cm2 for <1 y; 6.5 min, 1403 and 3.0 Gy.cm2 for 1 to <5 y; 5.9 min, 950 and 7.0 Gy.cm2 for 5 to <10 y; 5.7 min, 940 and 14.0 Gy.cm2 for 10 to <16 y, respectively. A large range of patient dose data is observed, depending greatly on procedure type and patient age. In all age groups the range of median FT, N and PKA values was 3.1-15.8 min, 579-1779 and 1.0-20.8 Gy.cm2 respectively. Consequently, the definition of LDRLs presents challenges mainly due to the multiple clinical and technical factors affecting the outcome. On the other hand the lack of paediatric IC DRLs makes the identification of good practices more difficult. A consensus is needed on IC procedures nomenclature and grouping in order to allow a common assessment and comparison of doses.

Accuracy of CT dose monitor values: a multicentric study.

Four hundred and ninety-five adult patients in 16 medical centres participated in this study aiming to investigate the congruence between the volume CT dose index (CTDIvol) monitor values and measured ones during common CT procedures, performed by 20 systems. Tube output CTDIair measurements were carried out on single and multislice scanners for any kV, slice thickness, mA and FOV combination used. The maximum/minimum ratio of measured CTDIvol values found to be 3.1, 3.5, 7.4, 7.5, 4.2, 11.3 and 5.5 for head base, head cerebrum, thorax, abdomen, pelvis, cervical spine and lumbar spine protocols, respectively. The mean divergence between the measured and displayed CTDIvol values was 4.2, 3.5, -1.0, 2.7, 4.9, -3.9 and -2.8 % for protocols as mentioned above, respectively. From the perspective of the number of detector rows of the scanners, the mean divergence was -6.7, -6.0, 0.8, -1.1, -0.4, -1.9, -5.3, 5.2 and 10.1 % for single, dual, 4, 6, 16, 24, 64, 128 and dual source 256-slice systems, respectively.

The effect of a combined tube current modulation system on dose delivered to patients undergoing thoracic and abdominal CT with a 128-slice scanner.

Combined tube current modulation techniques (such as Care Dose4D used in this study) during computed tomography (CT) procedures bring together the benefits of the angular and z-axis modulation techniques, measuring X-ray attenuation profile in the z-axis together with the data from the perpendicular x-y direction with a sophisticated algorithm. The purpose of this study was to investigate the radiation dose, in terms of computed tomography dose index (CTDI(vol)), delivered to patients during thoracic and abdominal CT using this technique and compare it with the corresponding CTDI(vol) of the fixed tube current CT technique. The results revealed a 5-32% dose reduction for chest CT and a dose reduction of 7.6-60% for the three-sequence abdominal CT scan of normal and overweight patients. In the case of obese patients a 15.4-18.7% dose increase for chest CT and a (-1.5) - (26.3)% dose increase for the three-stage abdominal examinations for females and males, respectively, was revealed.

Investigation of breast dose in five screening mammography centres in Greece.

The objectives of this study were to investigate the techniques currently used for screening mammography in Greece, to estimate the mean glandular dose (MGD) for establishing a baseline radiation dose database, to analyse the effects of various factors on MGD, and to compare the results with others in the literature. Five mammographic facilities and 250 women having as a routine screening mammogram one craniocaudal (CC) and one mediolateral oblique (MLO) projection in each breast were included in the study. The parameters recorded were age, weight, compressed breast thickness (CBT), tube potential (kV), tube loading (mA s) and MLO projection angle. Large differences were observed among the different mammography facilities, mainly in terms of the tube potential setting and the MLO angle used. The average MGD per exposure was 1.4 +/- 0.6 mGy while the respective averages separately for the CC and MLO projections were 1.2 +/- 0.5 and 1.5 +/- 0.7 mGy, respectively. The average MGD values recorded in this study were below the limit of 2 mGy established for the reference medium-sized breast of 4.5 cm CBT. However, the variety of techniques observed revealed the need for a nationwide survey concerning screening mammography in Greece.

High patient doses in interventional cardiology due to physicians' negligence: how can they be prevented?

Interventional cardiology procedures are usually associated with high patient doses and even deterministic radiation effects may occur. Expensive digital flat panels are preferably used to lower doses, and Athens General Hospital has recently installed one. However, this study shows that it is the cardiologists' practice that lowers patients' doses. Doses delivered to patients during two time periods (pre and after radiation protection training) on a total of 1196 coronary angiographies and 506 percutaneous transluminal coronary angioplasties were measured and analysed per cardiologist. Local reference levels (LRLs) were assessed and compared with the preliminary RLs provided by the European Research Program DIMOND. Results showed that although after the training patients' dose area product, fluoroscopy time, cumulative dose and number of images acquired were lowered, the situation remained unchanged for the cardiologist who delivered the highest doses. The question to answer next is how this bad practice can be prevented since no dose constraints apply to diagnostic or therapeutic procedures using ionising radiation.

Quality control measurements for fluoroscopy systems in eight countries participating in the SENTINEL EU coordination action.

Quality control (QC) is becoming increasingly important in relation to the introduction of digital medical imaging systems using X rays. It was, therefore, decided to organise and perform a trial on image quality and physical measurements. The SENTINEL toolkit for QC measurements of fluoroscopy systems containing equipment and instructions for their use in the assessment of dose and image quality circulated among participants in the trial. The participants reported on their results. In the present contribution, the impact of the trial on the selected protocols is presented. The Medical Physics and Bioengineering protocol appeared to be useful for QC, and also for digital systems. The protocol needs an additional section, or an addition to each section, to state compliance with the requirements. The circular cross-sections of the Leeds test objects need adaptation for rectangular flat panel detector (FPD) systems. Only one participant was able to perform the monitor test using MoniQA. This is due to the fact that assistance is required from the suppliers of the X-ray systems. This problem needs to be solved to apply MoniQA in practice.

Survey on performance assessment of cardiac angiography systems.

Advances in imaging technology have facilitated the development of increasingly complex interventional cardiac equipment. Consequently, there is a need for definitive equipment requirements. The aim of the study is to assess the performances of different cardiac angiographic systems. A questionnaire was sent to centres participating in SENTINEL Project to collect dosimetry data (typical entrance dose rate in fluoroscopy and imaging mode), image quality evaluations (low and high contrast resolutions) and KAP calibration factors. Results from this survey could contribute to the explanation of patient dose variability in angiographic cardiac procedures and to derive reference levels for cardiac angiographic equipment performance parameters.

Patient skin dose assessment during CT-guided interventional procedures.

The purpose of this study was to investigate patient skin doses in the most frequent computed tomography-guided interventional radiology procedures. The study includes 14 abdominal biopsies and 15 radiofrequency (RF) ablations. Patient skin dose was assessed by slow verification films. The technical factors recorded were: tube kilovoltage (kVp), tube load (mAs), slice thickness and the total number of slices (S). The median value of maximum entrance skin dose (ESD(M)) in biopsy was 108 mGy (9.5-282 mGy). S had a range of 4-152 with a median of 44 slices. Significant correlation was found between S and dose (r = 0.80). Median ESD(M) in RF ablation was 238 mGy (104-500 mGy). S had a range of 108-175 with a median of 155 slices. No significant correlation was found between S and dose. The large range of results show that a more extensive investigation should be performed. In summary, diagnostic procedures such as biopsy present patient skin doses that are relatively low. On the other hand, patient skin dose in RF ablation can be high and can reach values higher than the value that a slow verification film is capable of measuring (1.2 Gy). For these procedures, an alternative method should be investigated.

Commissioning and constancy protocols for digital angiographic units.

During the European Concerted Action SENTINEL 'Safety and Efficacy for New Techniques and Imaging using New Equipment to Support European Legislation', protocols for commissioning and constancy tests for dynamic digital flat detectors angiography units have been developed in order to harmonise practice among the European counties. The commissioning protocol includes measurements on X-ray tube and generator, patient and detector radiation dose and image quality. The constancy protocol is based on the dose and image quality measurements. The commissioning protocol was tested by SENTINEL partners who expressed an interest in checking their dynamic digital systems using this protocol. The results of basic tests are reported.

Level of patient and operator dose in the largest cardiac centre in Greece.

The objective of this study was to investigate the patient and staff doses in the most frequent interventional cardiology (IC) procedures performed in Onassio, the largest Cardiac Centre in Greece. Data were collected from three digital X-ray systems for 212 coronary angiographies, 203 percutaneous transluminal coronary angioplasties (PTCA) and 134 various electrophysiological studies. Patient skin dose was measured using suitably calibrated slow radiotherapy films and cardiologist dose using suitably calibrated thermoluminescent dosemeters placed on left arm, hand and foot. Patient median dose area product (DAP) (all examinations) ranged between 6.7 and 83.5 Gy cm2. Patient median skin dose in PTCA was 799 mGy (320-1660 mGy) and in RF ablation 160 mGy (35-1920 mGy). Median arm, hand and foot dose to the cardiologist were 12.6, 27 and 13 microSv, respectively, per procedure. The great range of radiation doses received by both patients and operators confirms the need for continuous monitoring of all IC techniques.

Patient dose in interventional radiology: a European survey.

Patient doses for a few common fluoroscopy-guided procedures in interventional radiology (IR) (excluding cardiology) were collected from a few radiological departments in 13 European countries. The major aim was to evaluate patient doses for the basis of the reference levels. In total, data for 20 procedures for about 1300 patients were collected. There were many-fold variations in the number of IR equipment and procedures per population, in the entrance dose rates, and in the patient dose data (total dose area product or DAP, fluoroscopy time and number of frames). There was no clear correlation between the total DAP and entrance dose rate, or between the total DAP and fluoroscopy time, indicating that a number of parameters affect the differences. Because of the limited number of patients, preliminary reference levels were proposed only for a few procedures. There is a need to improve the optimisation of IR procedures and their definitions and grouping, in order to account for their different complexities.

Comparison of patient doses in interventional radiology procedures performed in two large hospitals in Greece.

Purpose of the study was to determine patient doses in the most common interventional radiology (IR) procedures performed in two large Greek hospitals. A total of 164 patients who underwent 4 types of IR procedures were studied. Fluoroscopy time, total exposure time, number of frames, number of runs, radiation field size, and cumulative dose-area product (DAP) were recorded. The median DAP values for carotid arteriography and lower limb arteriography were 66 and 123 Gy cm2 for hospital 'A' and 21 and 49 Gy cm2 for hospital 'B'. For the cerebral arteriographies performed in hospital 'A', the median DAP was 116 Gy cm2, while for the hepatic embolizations performed in hospital 'B', it was 104 Gy cm2. The DAP values observed in hospital 'A' for carotid arteriography and lower limb arteriography were almost three times than those of hospital 'B'. From the data analysis, it is evident that dose optimization in hospital 'A' should be pursued through revision of the techniques used.

Comparison of a CCD and a flat-panel digital system in an Interventional Cardiology Laboratory.

We evaluated the performances of angiographic units equipped with a flat-panel (FP) detector and image intensifier (II) charge-coupled device (CCD) in the Interventional Cardiology (IC) Department. Entrance dose rate and dose per image, along with the dose at the II level were measured using 2 mm copper sheets to simulate a patient. Image quality (IQ) was evaluated using a phantom. Doses increased with fluoroscopy level changing from low to high. FP presented higher doses than CCD. Periodic measurements showed differences of up to 35%. Low mode IQ did not significantly differ from normal and high mode for both systems. Low fluoroscopy mode was decided to be used routinely. Both X-ray systems performed within international recommendations for conventional systems with the exception of higher cine radiation doses and II dose rates, stressing the fact that more studies are required to investigate whether dose levels should be adjusted.

On the use of DICOM cine header information for optimisation: results from the 2002 European DIMOND cardiology survey.

The paper explores the level of information contained within the DICOM header in images from various cardiology systems. Data were obtained in the European DIMOND survey on image quality (Italy, Ireland, Belgium, Greece and Spain). Images from five standard diagnostic cardiology procedures carried out in six European hospitals have been analysed. DICOM header information was extracted to a database in order to analyse how it could help in the optimisation of the procedures. The level of data contained in the headers differs widely between cardiology systems. None of the X-ray systems in the 2002 survey archives the dosimetric data in the DICOM header. The mean number of runs per procedure ranges between 7.5 and 15.4 and the mean number of frames per procedure between 575 and 1417. Differences in kVp, mA, pulse time, distances and C-arm angulations are substantial and suggest that there exists a wide range for optimisation.

Correlation of patient and staff doses in interventional cardiology.

The purpose of this study was to measure staff radiation doses in representative institutions of five European countries performing coronary angiographies (CA) and percutaneous transluminal coronary angioplasties (PTCA), as well as to investigate any correlation with patient doses. Patient doses were recorded in terms of dose-area product (DAP). Staff doses were measured by thermoluminescence dosemeters placed on the operator's left shoulder and left foot. Radiation protection measures were also recorded. Third quartile shoulder and foot doses were 90 and 66 microSv in CA, and 157 and 173 microSv in PTCA, respectively. Shoulder dose was poorly correlated with DAP in CA (R2 = 0.29) and only moderately correlated in PTCA (R2 = 0.69). DAP and foot dose correlation was poor both in CA (R2 = 0.16) and in PTCA (R2 = 0.02). Protective measures taken by staff varied between countries, which may explain the poor correlation of patient and staff radiation doses.

Does digital imaging decrease patient dose? A pilot study and review of the literature.

The potential for decreasing patient dose is one of the main arguments for the justification of the cost of digital imaging equipment. However, the literature review with respect to patient doses using digital imaging modalities, presents conflicting results. During this study, patients' entrance surface doses were measured for three simple radiographic examinations, in European centres equipped with a computed radiography digital system. Results showed that doses between centres varied from 30% for chest LAT to 250% for chest PA examination. With the digital image quality criteria still under discussion, and with the post-processing parameters and/or image documentations varying, any dose comparisons between conventional/digital systems, as well as dose comparisons between different centre using digital units, are difficult. Clinical trials are required in order to define reference levels associated with quality of digital image necessary to address specific clinical requirements.

Quality assurance (QA) procedures for software: evaluation of an ADC quality system.

Image viewing and processing software in computed radiography manipulates image contrast in such a way that all relevant image features are rendered to an appropriate degree of visibility, and improves image quality using enhancement algorithms. The purpose of this study was to investigate procedures for the quality assessment of image processing software for computed radiography with the use of existing test objects and to assess the influence that processing introduces on physical image quality characteristics. Measurements of high-contrast resolution, low-contrast resolution, spatial resolution, greyscale (characteristic curve) and geometric distortion were performed 'subjectively' by three independent observers and 'objectively' by the use of criteria based on pixel intensity values. Results show quality assessment is possible without the need for human evaluators, using digital images. It was discovered that the processing software evaluated in this study was able to improve some aspects of image quality, without introducing geometric distortion.

Radiation dose measurements to the interventional cardiologist using an electronic personal dosemeter.

The aim of this study was to investigate the use of an electronic personal dosemeter (EPD) worn by a senior cardiologist in an Interventional Cardiology (IC) Laboratory of a busy cardiac centre and how the results could help in the evaluation of radiation protection equipment used. Patient samples consist of 28 patients (10 coronary angiographies (CAs) and 18 percutaneous transluminal coronary angioplasties (PTCAs)). Patient dose was measured with a dose-area product (DAP) meter. Cardiologist radiation dose value written on the EPD as well as the protective equipment used was collected. Between patient and cardiologist dose, a significant correlation was found in CA and a moderate correlation in PTCA. Mean cardiologist effective dose E per procedure was found to be 0.2 microSv in CA and 0.3 microSv in PTCA. EPD proved to be an easy, direct and straightforward way to measure the radiation dose that the cardiologist receives in an IC laboratory.

Comparison of a conventional and a flat-panel digital system in interventional cardiology procedures.

The purpose of the study was to analyse the technical characteristics of a newly installed flat-panel fluoroscopy (FPF) system in an interventional cardiology (IC) department and compare it with an older conventional system. A patient survey was performed to investigate the radiation doses delivered by the X-ray systems. Finally, methods of technique optimization regarding the new digital system were investigated. Dose rates in all fluoroscopic and cine modes were measured and image quality assessed using a dedicated test tool. 200 patients were investigated, half using the conventional and half using the digital FPF system. Patient data collected were: sex, age, weight, height, dose-area product (DAP), fluoroscopy time (T) and total number of frames (F). Our results are: (1) Digital FPF system: high contrast resolution (HCR) is not affected by fluoroscopic mode, whereas low contrast resolution (LCR) is slightly decreased in the low mode. (2) The digital FPF system has 2.5 times better HCR than the conventional system, with 5 times lower dose in the fluoroscopy mode. (3) Median values of DAP, T and F, respectively, in coronary angiography (CA) are: 27.7 Gycm(2), 4.1 min and 876 for the digital and 39.3 Gycm(2), 5.3 min and 1600 for the conventional system. Median values for percutaneous transluminal coronary angioplasty (PTCA) are: 51.1 Gycm(2), 12.7 min and 1184 for the digital and 44.3 Gycm(2), 7.4 min and 1936 for the conventional system. Digital DAP in CA is reduced by 30%, suggesting that a dose reduction in the FPF system is possible. The results of the study concerning the FPF system lead to the conclusion that the lowest fluoroscopic mode and the lowest frame rate should be used in routine practice.