Phillips DoseWise: a set of techniques, programs and practices that ensure optimal image quality with minimum radiation.
Eleva system for fluoroscopy & Allura system for angiography incorporate DoseWise.
Smart beam management: Based on the selection of exam-type and patient-type, EPX-based program automatically selects the following:
- Radiographic exposure factors
- Focal spot size
- Spectral filtration
- Fluoroscopy type, dose and exposure rate
Radiographic Exposure Factors:
Grid-controlled Fluoroscopy (GCF) vs. Continous fluoroscopy, saves radiation. These are designed to maintain 70kV level even in very small patients.
IQX (Intelligent Exposure Control) rapidly regulates digital radiographic exposures when children are imaged.
Spectral beam filter:
"Soft radiation" (X-rays that enter patient's skin but do not have enough energy to reach image detector) are removed from the beam. Such filtration reduces dose to patient and personnel. Depending on patient size & type of exam, the filters are automatically inserted into the beam:
Copper spectral filters (0.1mm, 0.2 mm, 0.4 mm and 0.9 mm thickness)
&
Aluminum spectral filter (1 mm thickness)
Typically, 0.1 mm Cu filter reduces exposure by 50% & 0.2 mm by 70%.
Typically, 0.1 & 0.4 mm Cu filters are used in adult interventional procedures where long exposure times are common.
0.9 mm Cu filter is used for newborn & small children; and also for long EP procedures.
In cardiac & vascular procedures, 0.1 mm Cu filter & 0.4 mm Cu filter provide max. exposure of 10 R/min and 5 R/min respectively during fluoroscopy. (0.9 mm Cu filter provides 1.5 R/min max).
In standard pediatric radiology, 0.1 mm Cu filter provides best relationship best diagnostic images with lowest dose.
Customizing beam shape: 3 successive steps
1) Lead iris shape shutter (at the outlet port of X-ray tube)
2) Two Lead square shutters (positioned above 1)
3) Copper wedge filters within collimator
These shutters and wedges can be adjusted on Last-image-hold image (without using extra radiation to adjust these).
Adaptive Measuring Field (AMF):
When the field is panned through anatomic structures of varying (radio)opacity, brightness of fluoroscopic image changes. Automatic Exposure Control (AEC) - designed to maintain consistent image brightness level - would respond and increase X-ray dose to maintain brightness when very opaque object comes into the field. (Same occurs when collimator shutter are closed too small). AMF system continously monitors shutter position and uses sensors from the included areas only to set radiation output.
AEC lock-in helps to maintain image quality during panning through objects that are too dark and too light on the field. Thus, it eliminates "blooming".
Radiation-on time:
1) In-pulse radiation control (IQX) - Radiographic settings (tube voltage - kV, tube current - mA and pulse width - ms) are adjusted within the first millisecond of exposure.
2) Pulsing the beam during fluoroscopy (vs. Traditional, continous beam)
For fluoroscopy, GCF is used.
For angiography, IQX is used.
GCF (Grid-controlled Fluoroscopy):
GCF extends the in-pulse control concept to pediatric fluroscopy curves @ short pulse widths.
Production instant rise and fall of exposure (creating "square pulse"; achieved by DoseWise "Grid Switching") in stead of pulses with slight "ramp" in rise and fall (in "conventional pulse fluoroscopy") decreases radiation dose by 80-90%.
Grid switching also reduces soft radiation & motion blur.
(Two studies demonstrated GCF system reduced radiation dose between 4.6 - 17 times compared to conventional fluoroscopy: In children - Pediatr Radiol 2000;30:236-42 & In pigs - Radiol 2006;238:96-106).
Display of radiation exposure on physician's monitor display:
Air kerma dose levels
Dose Area Product (DAP) - measured from a meter located in X-ray tube collimator
Future: Display of patient entrance dose - monitored from predetermined points on patients body to warn when it approaches deterministic damage level.
