Review and investigation of automatic brightness/dose rate control logic of fluoroscopic imaging systems in cardiovascular interventional angiography.

In this article, we review automatic brightness control (ABC) for fluoroscopy imaging systems. Starting from the simple manual control, the discussion is extended to the kV-primary ABC system, and then to the most recent contrast-to-noise ratio optimized (CNR Optimized) automatic dose rate control system (ADRC). The nature of this review article is trifold. First, it describes the ABC/ADRC and associated circuits governing the operation of the fluoroscopy imaging chain. Second, we show the characteristics of a control logic from a radiation physics point of view. Third, we introduce the most recent activities in the evaluation of CNR-optimized fluoroscopy systems and the phantom design that would be compatible with the design concept of the ADRC. Because of these three subject items in the discussion process, this article is also educational in nature written for medical physicists and radiological technologists who might be less familiar with the design concept of fluoroscopy operation, specifically on the ABC and ADRC. We insert a few related matters associated with fluoroscopy automatic control circuits where they seem applicable and appropriate to enhance the understanding of fluoroscopy operation logic.

AAPM Task Group Report 272: Comprehensive acceptance testing and evaluation of fluoroscopy imaging systems.

Modern fluoroscopes used for image guidance have become quite complex. Adding to this complexity are the many regulatory and accreditation requirements that must be fulfilled during acceptance testing of a new unit. Further, some of these acceptance tests have pass/fail criteria, whereas others do not, making acceptance testing a subjective and time-consuming task. The AAPM Task Group 272 Report spells out the details of tests that are required and gives visibility to some of the tests that while not yet required are recommended as good practice. The organization of the report begins with the most complicated fluoroscopes used in interventional radiology or cardiology and continues with general fluoroscopy and mobile C-arms. Finally, the appendices of the report provide useful information, an example report form and topics that needed their own section due to the level of detail.

Characterization and verification of lead thickness of commercially available lead foil tape for the measurements of lead equivalency of radio-protective shields.

PURPOSE: Radiation protective apparatus is normally specified in "millimeter" of lead equivalence. Typically, it is less than 0.5 mmPb with the exception of lead eyeglasses, which may be 0.75 mmPb equivalent. Upon discovery of commercially available lead foil tape, manufactured by 3M™ "Lead Foil Tape 421" (LFT) which is designed for industrial utility applications. We set out to determine if this LFT can, indeed, be employed as the reference lead in the evaluation of lead equivalency of various protective apparatus. METHOD: The LFT is cut to appropriate size (50 mm × 50 mm) and stacked for varying the total lead thickness for the transmission measurements. The transmission curves are obtained following the geometry spelled out in ASTM Designation F3094-14 standards. The radiation beam qualities corresponding to modern cardiovascular angiography equipment in the range of 60~120 kVp, in increments of 10 kVp, and in combination with the spectral shaping filters of 0, 0.1, 0.2, 0.3, 0.6 and 0.9 mmCu were employed for characterization of the lead foil tape. The transmission data of lead pieces with known thicknesses (1/64", 1/32" and 3/64") are superimposed on the lead foil tape transmission curves to validate that the 3M™ LFT is indeed usable as 0.1 mm lead. RESULTS: The transmission ratio (data points) of lead pieces with known thicknesses at various radiation beam qualities mentioned above, fall right onto the transmission curves of 3M™ LFT with better than 2% accuracy. Therefore, it is indeed behaving like 0.1 mm thick lead sheet, based on the superimposed transmission curves. The 3M™ "Lead Foil Tape 421" is employed as the reference lead for evaluation of radiation protective apparatus at this institution. Verification of lead protective apparatus with unknown lead equivalence can now be determined with a high accuracy and certainty.

Evaluation and verification of a simplified lead equivalency measurement method.

PURPOSE: This technical note presents an inexpensive tool and method for determining lead equivalency using digital radiography x-ray equipment. METHODS: A test tool was developed using commercially available lead tape (3M™ Lead Foil Tape 421). The test tool consisted of nine varying lead thick squares arranged in a larger square (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 1.0 mm). It was imaged on a DR plate with a digital portable x-ray unit across a range of energies (60-120 kVp) and two beam filtrations. Lead equivalency was determined by using the linear relationship between dose to the detector and pixel values in the raw images. The lead equivalency of the tape was validated using known lead thicknesses (physically measured with caliper). Additional lead equivalency measurements were made for protective eyewear, a thyroid shield, and a lead apron. RESULTS: The test tool and method measured the two known lead thicknesses to be -9.7% to 7.1% different from the actual values across the range of energies under normal x-ray beam conditions and under a 1-mm copper filtered x-ray beam. The additional lead equivalency measurements of radiation protection apparel across energies ranged from -6% to 20% for both beam conditions when compared with the values provided by the manufacturer. CONCLUSION: This work validates the test tool and methodology as an inexpensive alternative to checking the lead equivalency of radiation protection apparel in a clinical setting. The methodology is equipment independent with a few prerequisites.

COVERING THE PATIENT'S ARM SUPPORT IN LEAD REDUCED THE RADIATION DOSE RATE TO THE CARDIOLOGISTS DURING PERCUTANEOUS CORONARY INTERVENTIONS: A PHANTOM STUDY.

The aim of the study was to estimate organ dose rate reduction to a female anthropomorphic phantom, which simulated the cardiologist, during percutaneous coronary interventions (PCI) when the patient's arm support was covered with 0.4-mm lead foil. Organ dose rates were determined using five radiation detectors inserted into the left eye, left thyroid, left breast, left liver lobe and uterus of the phantom. A male anthropomorphic phantom was placed on the examination table of an angiography system. Heart images of the patient phantom were acquired under 10 gantry angulations typical for PCI. The lead-covered arm support did not interfere with any of the cardiac images. The median organ dose rate reductions to the left eye, left thyroid, left breast, left liver lobe and uterus were 7.8, 36.0, 28.8, 35.7 and 33.5%, respectively. The lead-covered arm support substantially reduced scattered radiation to the female cardiologist without interfering with clinical environments.

Evaluation of lead equivalence of radiation protection apparatuses as a function of tube potential and spectral shaping filter.

PURPOSE: This study aims to evaluate the lead equivalence (LE) of radiation protective apparatuses under various combinations of tube potentials and spectral shaping filter. METHOD: In this study, the commercially available 3M™ Lead Foil Tape 421, with nominal lead thickness of 0.1 mm, was employed to determine the LE of four different radiation protective apparatuses. The LE of protective apparatus was determined by utilizing the X-ray transmission curves obtained with the lead foil tape at 60-120 kVp in combination with the spectral shaping filters of 0.1, 0.2, 0.3, 0.6, and 0.9 mmCu. The experimental setup and test method, for the transmission measurements with narrow beam geometry, was performed in accordance to ASTM Designation F2547-18 Standards. All measurements were obtained using cardiovascular interventional angiography system. RESULTS: A much larger discrepancies between the measured LE and stated (nominal) LE were observed at low tube potential (<70 kVp) for non-lead protective apparatus. At higher tube potentials (>80 kVp) and thicker spectral shaping filters, the measured LE appears to be more consistent with the manufacturer specified nominal thickness for the protective apparatus investigated. On the other hand, for the lead protective eyeglasses, the measured lead equivalence of both the lead side shield and the lens of eyeglasses (0.38 and 0.85 mmPb respectively) are consistent across all tube voltage. CONCLUSION: The conventional specification of LE without considering spectral shaping filter is a valid measure for tube voltages at and above 80 kVp. The measured LE generally exceed the specifications. The difference is most significant at lower tube potentials, and especially with thicker spectral shaping filters. At higher voltages (>100 kVp), the measured LE and the nominal LE are in good agreement with each other irrespective of the spectral shaping filter thickness.

Does gantry rotation time influence accuracy of volume computed tomography dose index (CTDIvol) in modern CT?

PURPOSE: The purpose of this study was to develop a gantry overrun corrected CTDIvol (cCTDIvol) dosimetry and evaluate the differences between the displayed CTDIvol (dCTDIvol), measured CTDIvol (mCTDIvol), and the cCTDIvol. METHODS AND MATERIALS: The each 8 rotation times between 275 and 1000ms of two CT scanners were investigated. Rotation time (Trot) and the beam-on time (Tbeam) in axial scanning were measured accurately to determine the gantry overrun time (Tover) as Tbeam-Trot. Subsequently, mCTDIvol was measured by using a 100mm ionization chamber and CTDI phantoms. Furthermore, we introduced a gantry overrun correction factor (Co=Trot/Tbeam) to obtain cCTDIvol. Upon completion of the data acquisition, the dCTDIvol and mCTDIvol were compared with the cCTDIvol. RESULTS: The discrepancies of Trot were 0.2±0.2ms as compared to the preset rotation times, and Tover was machine-specific and almost constant (22.4±0.5ms or 45.1±0.3ms) irrespective of the preset rotation time. Both dCTDIvol and mCTDIvol were increasingly overestimated compared to cCTDIvol as the faster the preset rotation time was selected (1.7-23.5%). CONCLUSION: The rotation time influences the accuracy of CTDIvol in modern CT, and should be taken into consideration when assessing the radiation output in modern CT.

Accuracy of gantry rotation time of less than 300 ms for modern MDCT systems.

The accuracy of gantry rotation times of less than 300 ms has been assessed for two "state-of-the art" MDCT systems. The rotation time was measured at selected nominal rotation times (275 and 280 ms) with a solid-state detector; Unfors Xi probe. The detector was positioned on the inner bottom of the gantry bore. Because a pair of two successive radiation peaks is necessary for determination of the rotation time, the radiation detection was performed with the helical scan mode of operation. Upon completion of the data acquisition, we determined the peak times with the Unfors Xi View software program to obtain the rotation time. The means and standard deviations of the measured rotation times were 275.3 ± 0.5 and 285.1 ± 0.4 ms, respectively. The inaccuracy of the rotation time was approximately 5 ms at most, which was comparable to that previously reported for slower rotation times.

Cancerogenesis Risks between 64 and 320 Row Detector CT for Coronary CTA Screening.

OBJECTIVES: This study compares cancerogenesis risks posed by the 64 row detector and the 320 row detector computed tomography scanners used during coronary computed tomography angiography (CCTA) following decennial screening guidelines. MATERIAL AND METHODS: Data of the radiation absorbed after CCTA by lung, thyroid, and female breast in patients between 50 and 70 years of age obtained from prior published literature for the 64 row CT scanner were compared with data from our study using 320 row detector CT scanner. Data from the 64 row and the 320 row detector CT scanners was used to determine lifetime attributable risks (LAR) of cancer based on the biological effects of ionizing radiation (BEIR) VII report. RESULTS: The relative reduction of LAR (%) for 50-, 60-, and 70-year-old patients undergoing scanning with the 320 row detector CT scanner was 30% lower for lung, and more than 50% lower for female breast when compared with results from 64 row detector CT scanner. The use of 320 row detector CT would result in a combined cumulative cancer incidence of less than 1/500 for breast in women and less than 1/1000 for lung in men; By comparison, this is much lower than other more common risk factors: 16-fold for lung cancer in persistent smokers, 2-fold for breast cancer with a first degree family member history of breast cancer, and 10-fold for thyroid cancer with a family member with thyroid cancer. Decennial screening would benefit at least 355,000 patients from sudden cardiac death each year, 94% of whom have significant coronary artery disease, with at least one stenosis >75%. LAR for thyroid cancer was negligible for both scanners. CONCLUSION: Lung and female breast LAR reductions with 320 row detector compared with 64 row detector CT are substantial, and the benefits would outweigh increased cancer risks with decennial screening in the age group of 50-70 years.

Differences in behavior of tube current modulation techniques for thoracic CT examinations between male and female anthropomorphic phantoms.

Our objective was to investigate the differences in behavior of tube current modulation (TCM) techniques for thoracic CT examinations between male and female anthropomorphic phantoms. The phantoms were scanned with an automatic exposure control system in the longitudinal (z-) and angular-longitudinal (xyz-) TCM, in addition to the fixed-mA which was used as a reference. Axial dose distributions were measured at the levels of the breasts and the diaphragm, and longitudinal dose distributions were measured from the thoracic-inlet level to the diaphragm level at the center and periphery of the phantoms by use of eight solid-state detectors. Image noise was quantitatively measured continuously from the top to the bottom images of the phantoms. With the male phantom, the percentage of average absorbed dose with the xyz-TCM mode compared to the z-TCM mode was 90.2 % at the level of the nipples. This value was significantly smaller than that for the female phantom (95.6 %, P < 0.0001). With either phantom, the percentage of absorbed doses in the longitudinal direction with the xyz-TCM mode compared to the z-TCM mode at the center of the phantom was almost the same as the percent ratio at the periphery of the phantom. Therefore, the effect of xyz-TCM was less pronounced with the female phantom, especially on the reduction of the breast dose. The increase of image noise at the level of the supraclavicular fossa (in the male phantom) and at the level of the diaphragm (both phantoms) could not be avoided with the use of TCM techniques.

Functionality and operation of fluoroscopic automatic brightness control/automatic dose rate control logic in modern cardiovascular and interventional angiography systems: a report of Task Group 125 Radiography/Fluoroscopy Subcommittee, Imaging Physics Committee, Science Council.

Task Group 125 (TG 125) was charged with investigating the functionality of fluoroscopic automatic dose rate and image quality control logic in modern angiographic systems, paying specific attention to the spectral shaping filters and variations in the selected radiologic imaging parameters. The task group was also charged with describing the operational aspects of the imaging equipment for the purpose of assisting the clinical medical physicist with clinical set-up and performance evaluation. Although there are clear distinctions between the fluoroscopic operation of an angiographic system and its acquisition modes (digital cine, digital angiography, digital subtraction angiography, etc.), the scope of this work was limited to the fluoroscopic operation of the systems studied. The use of spectral shaping filters in cardiovascular and interventional angiography equipment has been shown to reduce patient dose. If the imaging control algorithm were programmed to work in conjunction with the selected spectral filter, and if the generator parameters were optimized for the selected filter, then image quality could also be improved. Although assessment of image quality was not included as part of this report, it was recognized that for fluoroscopic imaging the parameters that influence radiation output, differential absorption, and patient dose are also the same parameters that influence image quality. Therefore, this report will utilize the terminology "automatic dose rate and image quality" (ADRIQ) when describing the control logic in modern interventional angiographic systems and, where relevant, will describe the influence of controlled parameters on the subsequent image quality. A total of 22 angiography units were investigated by the task group and of these one each was chosen as representative of the equipment manufactured by GE Healthcare, Philips Medical Systems, Shimadzu Medical USA, and Siemens Medical Systems. All equipment, for which measurement data were included in this report, was manufactured within the three year period from 2006 to 2008. Using polymethylmethacrylate (PMMA) plastic to simulate patient attenuation, each angiographic imaging system was evaluated by recording the following parameters: tube potential in units of kilovolts peak (kVp), tube current in units of milliamperes (mA), pulse width (PW) in units of milliseconds (ms), spectral filtration setting, and patient air kerma rate (PAKR) as a function of the attenuator thickness. Data were graphically plotted to reveal the manner in which the ADRIQ control logic responded to changes in object attenuation. There were similarities in the manner in which the ADRIQ control logic operated that allowed the four chosen devices to be divided into two groups, with two of the systems in each group. There were also unique approaches to the ADRIQ control logic that were associated with some of the systems, and these are described in the report. The evaluation revealed relevant information about the testing procedure and also about the manner in which different manufacturers approach the utilization of spectral filtration, pulsed fluoroscopy, and maximum PAKR limitation. This information should be particularly valuable to the clinical medical physicist charged with acceptance testing and performance evaluation of modern angiographic systems.

Radiation safety program for the cardiac catheterization laboratory.

The Society of Cardiovascular Angiography and Interventions present a practical approach to assist cardiac catheterization laboratories in establishing a radiation safety program. The importance of this program is emphasized by the appropriate concerns for the increasing use of ionizing radiation in medical imaging, and its potential adverse effects. An overview of the assessment of radiation dose is provided with a review of basic terminology for dose management. The components of a radiation safety program include essential personnel, radiation monitoring, protective shielding, imaging equipment, and training/education. A procedure based review of radiation dose management is described including pre-procedure, procedure and post-procedure best practice recommendations. Specific radiation safety considerations are discussed including women and fluoroscopic procedures as well as patients with congenital and structural heart disease.

Absorbed radiation dose in radiosensitive organs during coronary CT angiography using 320-MDCT: effect of maximum tube voltage and heart rate variations.

OBJECTIVE: The purpose of this article is to estimate the absorbed radiation dose in radiosensitive organs during coronary MDCT angiography using 320-MDCT and to determine the effects of tube voltage variation and heart rate (HR) control on absorbed radiation dose. MATERIALS AND METHODS: Semiconductor field effect transistor detectors were used to measure absorbed radiation doses for the thyroid, midbreast, breast, and midlung in an anthropomorphic phantom at 100, 120, and 135 kVp at two different HRs of 60 and 75 beats per minute (bpm) with a scan field of view of 320 mm, 400 mA, 320 × 0.5 mm detectors, and 160 mm collimator width (160 mm range). The paired Student's t test was used for data evaluation. RESULTS: At 60 bpm, absorbed radiation doses for 100, 120, and 135 kVp were 13.41 ± 3.59, 21.7 ± 4.12, and 29.28 ± 5.17 mGy, respectively, for midbreast; 11.76 ± 0.58, 18.86 ± 1.06, and 24.82 ± 1.45 mGy, respectively, for breast; 12.19 ± 2.59, 19.09 ± 3.12, and 26.48 ± 5.0 mGy, respectively, for lung; and 0.37 ± 0.14, 0.69 ± 0.14, and 0.92 ± 0.2 mGy, respectively, for thyroid. Corresponding absorbed radiation doses for 75 bpm were 38.34 ± 2.02, 59.72 ± 3.13, and 77.8 ± 3.67 mGy for midbreast; 26.2 ± 1.74, 44 ± 1.11, and 52.84 ± 4.07 mGy for breast; 38.02 ± 1.58, 58.89 ± 1.68, and 78 ± 2.93 mGy for lung; and 0.79 ± 0.233, 1.04 ± 0.18, and 2.24 ± 0.52 mGy for thyroid. Absorbed radiation dose changes were significant for all organs for both tube voltage reductions as well as for HR control from 75 to 60 bpm at all tube voltage settings (p < 0.05). The absorbed radiation doses for the calcium score protocol were 11.2 ± 1.4 mGy for midbreast, 9.12 ± 0.48 mGy for breast, 10.36 ± 1.3 mGy for lung, and 0.4 ± 0.05 mGy for thyroid. CONCLUSION: CT angiography with 320-MDCT scanners results in absorbed radiation doses in radiosensitive organs that compare favorably to those previously reported. Significant dose reductions can be achieved by tube voltage reductions and HR control.

Extraction of tube current values from DICOM CT images for patient dose estimation.

PURPOSE: When CT examinations are conducted with automatic mA modulation (z-axis modulation), the tube current (mA) may vary from one CT slice to next, i.e., mA is no longer a fixed constant. Hence, patient dose calculation is no longer a straightforward process. The purpose of this article is to show how the mA information may be extracted from DICOM CT images without having to manually read off "mA values" from the displayed images one at a time. METHODS: A statistical programming language called "R," which is capable of reading DICOM files, is employed to extract the mA values from a series of DICOM CT images. This task is carried out with a "script" designed to read the mA values from the DICOM CT images and generate a file in "delimited ASCII" format. This file can be imported into a spreadsheet program such as Excel (a Microsoft spreadsheet program) for further processing, calculation, and chart production. A CT examination of the chest was selected to carry out this operation for demonstration purposes. RESULTS: The "script" generated a delimited ASCII "file" which is a two column data sheet with the slice location and its corresponding mA values. After the file is imported into Excel for calculation, and with other pertinent scan parameters, the average mA can now be plugged into a CT dosimetry calculation program such as ImPACT for calculation of CTDI*w, CTDIvol, dose-length-product, and critical organ doses. Furthermore, a graphical presentation of the "mA" vs slice location can be produced with Excel. The chart generated by Excel shows the variation in tube current as a function of slice location. The area under the mA curve is equal to a rectangle of "average mA" x "distance". Here, the distance is the range covered by the CT scan. CONCLUSIONS: The script that the authors have written is able to extract mA values from DICOM CT images, generating a delimited ASCII file for further processing with Microsoft Excel spreadsheet program. After the DICOM images are imported into a personal computer, this semiautomated process of extracting mA values enabled the authors to perform dose calculation for patients undergoing CT examination scanned with automatic mA modulation control.

A review of factors that affect artifact from metallic hardware on multi-row detector computed tomography.

Artifact arising from metallic hardware can present a major obstacle to computed tomographic imaging of bone and soft tissue and can preclude its use for answering a variety of important clinical questions. The advent of multirow detector computed tomography offers new opportunities to address the challenge of imaging in the presence of metallic hardware. This pictorial essay highlights current strategies for reducing metallic hardware artifacts and presents some illustrative clinical cases.

Operation logic and functionality of automatic dose rate and image quality control of conventional fluoroscopy.

New generation of fluoroscopic imaging systems is equipped with spectral shaping filters complemented with sophisticated automatic dose rate and image quality control logic called "fluoroscopy curve" or "trajectory." Such fluoroscopy curves were implemented first on cardiovascular angiographic imaging systems and are now available on conventional fluoroscopy equipment. This study aims to investigate the control logic operations under the fluoroscopy mode and acquisition mode (equivalent to the legacy spot filming) of a conventional fluoroscopy system typically installed for upper-lower gastrointestinal examinations, interventional endoscopy laboratories, gastrointestinal laboratory, and pain clinics.

Technical advances of interventional fluoroscopy and flat panel image receptor.

In the past decade, various radiation reducing devices and control circuits have been implemented on fluoroscopic imaging equipment. Because of the potential for lengthy fluoroscopic procedures in interventional cardiovascular angiography, these devices and control circuits have been developed for the cardiac catheterization laboratories and interventional angiography suites. Additionally, fluoroscopic systems equipped with image intensifiers have benefited from technological advances in x-ray tube, x-ray generator, and spectral shaping filter technologies. The high heat capacity x-ray tube, the medium frequency inverter generator with high performance switching capability, and the patient dose reduction spectral shaping filter had already been implemented on the image intensified fluoroscopy systems. These three underlying technologies together with the automatic dose rate and image quality (ADRIQ) control logic allow patients undergoing cardiovascular angiography procedures to benefit from "lower patient dose" with "high image quality." While photoconductor (or phosphor plate) x-ray detectors and signal capture thin film transistor (TFT) and charge coupled device (CCD) arrays are analog in nature, the advent of the flat panel image receptor allowed for fluoroscopy procedures to become more streamlined. With the analog-to-digital converter built into the data lines, the flat panel image receptor appears to become a digital device. While the transition from image intensified fluoroscopy systems to flat panel image receptor fluoroscopy systems is part of the on-going "digitization of imaging," the value of a flat panel image receptor may have to be evaluated with respect to patient dose, image quality, and clinical application capabilities. The advantage of flat panel image receptors has yet to be fully explored. For instance, the flat panel image receptor has its disadvantages as compared to the image intensifiers; the cost of the equipment is probably the most obvious. On the other hand, due to its wide dynamic range and linearity, lowering of patient dose beyond current practice could be achieved through the calibration process of the flat panel input dose rate being set to, for example, one half or less of current values. In this article various radiation saving devices and control circuits are briefly described. This includes various types of fluoroscopic systems designed to strive for reduction of patient exposure with the application of spectral shaping filters. The main thrust is to understand the ADRIQ control logic, through equipment testing, as it relates to clinical applications, and to show how this ADRIQ control logic "ties" those three technological advancements together to provide low radiation dose to the patient with high quality fluoroscopic images. Finally, rotational angiography with computed tomography (CT) and three dimensional (3-D) images utilizing flat panel technology will be reviewed as they pertain to diagnostic imaging in cardiovascular disease.

Radiation dose reduction in chest CT: a review.

OBJECTIVE: This article aims to summarize the available data on reducing radiation dose exposure in routine chest CT protocols. First, the general aspects of radiation dose in CT and radiation risk are discussed, followed by the effect of changing parameters on image quality. Finally, the results of previous radiation dose reduction studies are reviewed, and important information contributing to radiation dose reduction will be shared. CONCLUSION: A variety of methods and techniques for radiation dose reduction should be used to ensure that radiation exposure is kept as low as is reasonably achievable.

The operation logic of automatic dose control of fluoroscopy system in conjunction with spectral shaping filters.

The introduction and extensive application of spectral shaping filters during fluoroscopic imaging procedures have decreased the patient skin entrance exposures (air kerma) dramatically while the image quality is optimized and maintained. The purpose of this article is to demonstrate and understand the functionality and operation of fluoroscopic automatic dose rate control logic installed on a modern cardiovascular angiography system, as seen from the equipment operation point of view. The fluoroscopic "patient" entrance exposure (air kerma) rate and the flat panel image receptor input exposure (air kerma) rate were obtained for reference and future application.

The influence of angiography table shields and height on patient and angiographer irradiation during interventional radiology procedures.

PURPOSE: To quantify the influence of angiography table height on patient and angiographer irradiation, as compared with other routine protective measures such as the use of protective shields hanging at the tableside and from the ceiling of angiography suites. METHODS: An experimental study was carried out in which a phantom (substitute for a human body) placed on the angiography table was irradiated by pulsed fluoroscopy. Entrance exposure rates were measured at the phantom surface (surrogate of patient skin exposure by incident X-ray beam) and at 60 cm from the phantom (analog to angiographer skin exposure by scatter). Exposure rates were measured at levels corresponding to the knees, testes, waist, xyphoid appendix, shoulders, and eyes of an angiographer 178 cm tall. Measurements were repeated at angiography table heights of 85, 95, 105, and 110 cm from the floor, with and without protective shields. RESULTS: Moving the table from its highest to lowest position increased by 32% the phantom entrance exposure but decreased scatter to the angiographer. Scatter to the angiographer could be reduced most by using the protective shields (30-105 times less), but low table heights provided relatively more important protection (412-1121 muSv/hr reduction, or 15-72% scatter reduction) when shields were not used (e.g., for unprotected regions of the angiographer's body such as the hands). CONCLUSION: Working at lower table heights provides a little additional protection to exposed body parts of angiographers, at the cost of somewhat higher patient exposure. Although small, this incremental protection could be clinically relevant in the long term. The choice of table position should be a compromise based on multiple factors, including at least patient exposure, scatter to angiographers, and angiographer comfort.