Angiography Approaches to Dose Reduction
Dose Reduction Advances in Angiography
This section focuses on various technologies that Siemens has implemented or developed to reduce, monitor, and report the radiation dose applied during interventional procedures.
Siemens strives to implement all dose-saving, monitoring, and reduction methods available in the interventional market today. As a leader in the field of dose reduction, we consistently develop our own solutions. As such, we were the first to implement several features that save and monitor the radiation dose in the interventional routine. In addition, we are a leading vendor to offer these cutting-edge solutions for a large number of features.
Our products clearly follow the ALARA principle (As Low As Reasonably Achievable) to reduce radiation dose to the lowest possible level. This desire for as little radiation exposure as possible is at the heart of the CARE (Combined Applications to Reduce Exposure) research and development philosophy.To maintain our leading position, and to improve health care for patients, we cooperate closely with experts at universities, and at public and private radiology centers all over the world – to convert research developments into practical components of everyday clinical routine.
In addition to implementing the newest technology, dose reduction efforts in angiography require training to become familiar with reduction methods and factors. We therefore attempt to make our dose-saving products as transparent as possible. We also provide a broad range of dose-monitoring products to interventionalists and technologists, and offer an ongoing selection of seminars and resources on dose reduction.
Figure 1 outlines our dose-saving, monitoring, and reporting products and tools for angiography, which are all available with all Artis systems.
Features pioneered by Siemens to reduce dose in AX include:
- CARE features
- Crystalline silicon detector
Dose Saving in Angiography – CARE
Reducing the dose during interventional procedures is not only critical for the patient, but also for the cardiologist and staff in the examination room. By integrating a broad range of dose-saving features into the Artis zee, Siemens minimizes the dose to both patients and the interventional staff.
Variable Fluoro Pulse Rates - CAREvision
CAREvision provides variable fluoro pulse rates. The pulsing frequency of the Artis systems can be adapted according to the clinical need: from 30 pulses per second (p/s) in various steps, down to 0.5 p/s. This is the easiest way to reduce exposure to the patient. A reduction to half pulse rate reduces the dose by about half. The reduction from 30 p/s to 7.5 p/s results in a dose saving of 75%2 (Figure 2).
Continuous Variable Filter Adjustment - CAREfilter
CAREfilter achieves skin dose reduction by allowing adjustment of the filter thickness. Additional copper filters reduce the skin dose through beam hardening. The variable filtration, 0.2 to 0.9 mm during fluoroscopy and 0.0 to 0.9 mm during digital acquisition, is adjusted automatically according to the absorption of the patient entrance dose along the path of the X-ray beam through the patient. This automatic filter insertion always maintains the lowest skin dose possible without degrading image quality. The filter selection is shown on the data display section of the monitor. Increasing prefiltering from 0.2 to 0.9 mm at 70 kV results in a dose saving of approximately 50% (Figure 3).
Radiation-Free Collimator and Filter Setting - CAREprofile
Using the last image hold (LIH) as a reference, CAREprofile allows radiation-free collimation and semitransparent filter position setting to precisely target the region of interest.
Radiation-Free Positioning - CAREposition
CAREposition provides radiation-free object positioning. Graphic display of the outline of the upcoming image allows panning the table without fluoroscopic radiation exposure (Figure 5).
CAREprofile and CAREposition can reduce the total fluoroscopy time by 0.5 to 3 minutes. This can results in a dose saving for normal fluoro at a SID of 100 cm and a phantom and table equivalent thickness of 207 mm at 70 kV of 12 to 70 mGy.1
1 Nickoloff et al., Cardiovasc Intervent Radiol (2007) 30:168-176.
The operator can easily reduce the radiation exposure by changing the fluoroscopy protocol – i.e. by switching tableside ECC/TSC1 from “Fluoro med” to “Fluoro low” during fluoroscopy using the touch screen; or by increasing the exposure to “Fluoro high” because of a thick object or a steep angulation (Figure 6).
1 ECC = Examination Control Console, TSC = Touch Screen Control.
Switching between the three different fluoroscopy modes can be done tableside in the Examination tab card (see Figure 6) or in the control room in the Examination Set (see Figure 6). “Fluoro low” typically means half dose compared to “Fluoro med.”
For especially dose-sensitive patients, it is possible to generate a special low-dose acquisition protocol. An acquisition pedal of the footswitch can be configured as a low-dose acquisition alternative to the ECC/TSC (Figure 7).
A dose saving of 67%1 can be achieved by using an acquisition dose of 80 nGy/f instead of 240 nGy/f for interventional cardiology and an acquisition dose of 0.8 μGy/f instead of 2.4 μGy/f for interventional radiology.
1Product Dose Reduction Claims for Artis Q / Q.zen.
Low-Dose syngo DynaCT
The low-dose syngo DynaCT protocol achieves acceptable image quality at lowest possible dose values in a lot of cases (Figure 66). This protocol is for radiosensitive patients, such as pediatric patients, and provides adequate diagnostic image quality. In clinical practice, the balance between image quality and dose has to be considered. For the prerequisites mentioned above, a five-second high-contrast DR rotational 3D run applying 0.36 μGy/f can be reduced to 0.1 μGy/f. Switching from 0.36 μGy/f to 0.1 μGy/f results in a dose saving of up to 72%.1 Low-dose syngo DynaCT can be achieved with an effective dose of 0.1 mSv.
In combination with syngo InSpace3D/3D Fusion, low-dose syngo DynaCT results can be fused with diagnostic preinterventional CT, MR, or PET•CT results. These fused data sets provide an excellent basis for planning and guidance during interventional procedures.
1Product Dose Reduction Claims for Artis Q / Q.zen.
Slab Reconstruction for syngo DynaCT
Slab mode allows you to collimate the image from top to bottom before doing the 3D rotational run (Figure 9). The benefits are lower dose, because of the small exposed area, with better image quality, because of less scattered radiation.
Fluoro Loop – Storage of Fluoroscopic Scenes
The Artis systems can store the last 1024 images from fluoroscopy to hard disk (Figure 10). This feature can be used for documentation, and can make additional digital acquisitions unnecessary. The operator only has to press one button at the ECC/TSC console.
For specific cardiac protocols, using fluoroscopic recording instead of digital acquisition results in a dose saving by a factor of 8 to 10 per minute at 15 fps.1
1Nickoloff et al., Cardiovasc Intervent Radiol (2007) 30:168-176.
A simple way to reduce the dose in pediatric examinations, especially for babies or very thin patients, when scatter radiation can be expected to be negligible, is to remove the scatter grid in the flat detector housing (Figure 11).
The grid factor (i.e. the absorption of primary radiation due to the anti-scatter grid compared to free air) is 1.35, which translates into a dose saving of 26% when removing the grid.
Monitoring the patient dose is another element in controlling radiation exposure. To keep the burden of this task off the interventionalist, the Artis systems are equipped to monitor patient dose in various ways. This allows for more transparency during and after the procedure as to how much radiation was applied. The following sections discuss how to monitor dose with the Artis systems.
Making dose visible - CAREwatch
CAREwatch displays the dose values during the patient examination on the image monitors in the examination room and also in the control room (Figure 12).
- When radiation is off, the dose area product and the accumulated dose at the IRP (Figure 12) are displayed.
- When radiation is on, the dose area product and dose rate at the IRP are displayed.
Multilevel patient entrance dose warning - CAREguard
CAREguard provides an effective way to control patient entrance dose (i.e. air kerma at the patient entrance reference point PERP1). Three dose threshold values (low, medium, and high) can be individually defined. If the accumulated patient entrance dose exceeds one of the defined thresholds:
- An audible warning sound is given
- A patient entrance dose indicator on the live display flashes
- A warning popup is displayed on the ECC/touch screen
1PERP = Patient entrance reference point = IRP.
Peak patient entrance dose monitoring - CAREmonitor
CAREmonitor shows the accumulated peak patient entrance dose according to the current projection in the form of a fill indicator on the live monitor. Any change to the C-arm, table, SID, zoom, or collimator prompts the system to automatically update the calculation. CAREmonitor can help to avoid skin burns during long-lasting interventions.
More and more countries and authorities require the reporting of patient exposure following an intervention. To meet current and future regulations, Artis systems allow effective reporting of dose exposure and thus enable enhanced in-house dose reporting and analysis.
Patient Examination Protocol
After the patient has been examined, an examination or patient protocol is stored together with acquired images. The complete information for each run is stored. At the end of the protocol, the dose information is listed: number of exposures, total fluoro time, total dose area product, and total dose at IRP. These values are separated per plane in the lines below (Figure 16).
The examination protocol can be sent to a PACS system and printed as an image. It can also be stored and sent as a DICOM structured report for further evaluation.
DICOM Structured Report - CAREreport
CAREreport, the DICOM structured dose report, contains all patient demographics, procedure and dose information. Using commercially available programs or in-house software, this information can be filtered for further processing, such as dose analysis (Figure 17).
CAREreport provides consistent dose reporting and prepares for future potential legal requirements.
Focused Power – GIGALIX1
The GIGALIX X-ray tube has been designed around a unique flat emitter technology that generates powerful short pulses. Compared to filament technology, the higher maximum current of the flat emitter enables CLEARpulse and enhances image quality in challenging situations such as with obese patients or in steep angulations. The small square focal spots of the GIGALIX result in higher spatial resolution for all clinical applications and help to better visualize small devices and vessels.
Together with the higher contrast resolution, this results in up to 70% better visibility of small devices2.
With CLEARpulse, the pulse length can be shortened. This allows visualizing moving objects such as coronary vessels more sharply.
CLEARpulse also optimizes the X-ray spectrum by lowering the required tube voltage and allowing for additional filtration. Together with small focal spots, this generates equal image quality with up to 60% less dose2.
The GIGALIX X-ray tube in the Artis Q product line scores a double win: enhanced image quality at a significantly lower dose for both patients and staff.
1Only available with Artis Q/Q.zen.
2Compared to previous X-ray tube technology.
Crystalline silicon detector1 - High Sensitivity for Ultra-Low-Dose Imaging
The active matrix of the Artis Q.zen detector allows the signal to be amplified directly where it is generated at each pixel of the matrix. This on-pixel amplification enhances the signal to electronic noise ratio compared to amorphous silicon detectors significantly and for the first time enables imaging with very low radiation, down to only 6 nGy per pulse.
We call this new acquisition mode “ultra-low-dose imaging”.
The image guidance of EP catheters can now be done with ultra-low-dose imaging. This reduces radiation to the patient and personnel in the room, which is especially important for complex, longlasting procedures such as pulmonary vein isolations. The detector delivers clear image quality even when using other systems in the room, such as mapping systems, without additional shielding.
When treating babies and children, reducing radiation is of particular importance. Especially for complex interventional procedures in pediatric cardiology and radiology, ultra-low-dose imaging might help to reduce the radiation significantly. The ultra-fast readout technology of the new crystalline silicon detector allows for higher frame rates in 3D imaging, up to 99 f/s. In addition, the crystalline silicon detector provides more coverage compared to small cardiology detectors, allowing views of the entire heart.
1Only available with Artis Q.zen.