In this presentation,
we summarized radiation dose reduction technologies in CT.
Radiation Dose Management with Dose Reduction Strategies
1.
ALARA Principle:
One of the main principles in renewal of radiology equipment.
2. Automatic Tube Potential Selection (ATPS):
On the basis of the examination type and the patient size,
the algorithm determines the voltage that will achieve the desired image quality at the lowest CTDIvol (Figs.
2).
Fig. 2: Dose reduction can be maintained by decreasing tube voltage.
3.
Automatic Tube Exposure Control (AEC):
AEC allows automatic modulation of tube current according to patient size and shape (Table 2).
AEC types:
- Angular (X- and Y- axis) modulation (Rotational)
- Z- axis modulation (Longitudinal)
- Combined (X,
Y and Z-axis)
Table 2: AEC systems.
Vendor |
AEC system Name |
Operator Controlled Parameter |
Z-Modulation |
Angular Axis Modulation |
Siemens |
Care Dose 4D |
Image quality Reference mAs |
Yes |
Yes |
Phillips |
Dose Right |
Reference Image |
Yes |
Yes |
Toshiba |
Save Exposure 3 D |
Target Image Quality level |
Yes |
Yes |
GE |
Auto mA |
Noise Index |
Yes |
No |
GE |
Smart mA |
Noise Index |
Yes |
Yes |
5.
Organ-based Dose Modulation
Decreased anterior current with respect to posterior (Fig.
3)
Critical organs in anterior aspect such as the cornea,
thyroid,
and breast are spared
Dose savings to anterior radiosensitive organs: %27-50
Fig. 3: Organ-based modulation reduces dose in cornea, thyroid and breast.
References: Siemens Healthcare, Guide to Right Dose
6.
Iterative Reconstruction (IR)
Computationally complex method of CT postprocessing (Fig.
4)
Reduce image noise by statistical or optic modelling (Table 3).
Strength of IR can be changed (Fig.
5).
Fig. 4: Iterative reconstruction.
Table 3: Iterative reconstruction types.
IR Types |
Vendor |
Year |
Data |
Reconstruction method |
iDose |
Phillips |
2011 |
Raw data,
image space |
Statistical |
IMR |
Phillips |
2013 |
Raw data,
image space |
Model-based |
ASiR |
GE |
2008 |
Image and raw data |
Statistical |
Veo (MIBR) |
GE |
2012 |
Projection |
Model based |
AIDR |
Toshiba |
2010 |
Raw data |
Statistical |
AIDR-3D |
Toshiba |
2012 |
Image and raw data |
Statistical |
IRIS |
Siemens |
2010 |
Image space |
Statistical |
SAFIRE |
Siemens |
2011 |
Raw data,
image space |
Statistical |
ADMIRE |
Siemens |
2013 |
Raw data,
image space |
Model based |
Fig. 5: IR in abdominal CT. Dose reduced from
DLP: 723 to DLP: 333 with SAFIRE.
6.
Adaptive Dose Shielding (ADS)
The pre-patient collimator asymmetrically opens and closes at the beginning and end of each spiral scan
ADS temporarily blocks those parts of the X-ray beam that are not used for image reconstruction (Fig.
6).
Fig. 6: Adaptive Dose Shielding.
References: Siemens Healthcare, Guide to Right Dose
7.
Pediatric CT
A low fixed or automatic tube current or potential
AEC techniques
IR
Pediatric beam-shape filter or bow-tie filter
Dedicated CT equipment with optimal protocols
8.
Automated Dose Monitoring System
Automatically extract CT dose metrics from the CT examinations
Compile dose metrics in a searchable and analyzable database dose tracking system
Receive alerts when exams have exceeded pre-defined threshold levels
Provide a plan to deliver just the right dose for the right clinical outcomes
Quantify results of protocol optimization activities