Post on 20-Mar-2018
transcript
Mark P. Supanich, PhD
Henry Ford Health System
Detroit, MI
marks@rad.hfh.edu
CT HEAD PROTOCOLS
DISCLOSURES• Research Grant: Siemens AG
• All patient images acquired and used under IRB approval
OUTLINE• Dose and image quality requirements
• Protocol examples from vendors
• Axial vs. Helical and other scanning considerations
• Is 120 kVp the optimal tube potential?
• Pediatric Head CT
ACR CT ACCREDITATION PROGRAM DOSE LIMITS• Based Solely on CTDIvol (not DLP)• Two levels:
• Reference level and Pass/Fail level
• Exam Ref Level Pass/Fail Level• Adult Head 75 mGy 80 mGy• Adult Abdomen 25 mGy 30 mGy• All values pertain to a single phase, NOT cumulative from multi-phase exams
• Low contrast CNR must be >= 1
ACR DOSE INDEX REGISTRY DATA• 295 Facilities
• More than 300,000 Adult Non-Contrast Head CTs
• Mean CTDIvol~ 57 mGy
• 25th Percentile: 46 mGy
• Median: 55 mGy
• 75th Percentile: 65 mGy
• No information on image thickness
GE – TYPICAL AAPM CTWGNP PROTOCOLSAxial Helical
Nominal Collimation 20 20
Pitch NA ~0.5
kVp 140 Base/120 Cerebrum 120
Iterative Level 40% (if available) 40% (if Available)
AEC? No No
Typical CTDIvol (mGy) 55 Base/60 (40 w/ ASIR) Cerebrum
54(35)
Image Thickness (mm) 5 mm 4 mm
HFHS GE VCT PROTOCOLCTDIvol ~ 60 mGy, 2.5 mm Image Thickness, Axial Acquisition, uses AEC, Nominal
Collimation Width= 20 mm
HITACHI – TYPICAL AAPM CTWGNP PROTOCOLS
Axial Helical
Nominal Collimation 20 30
Pitch NA 1
kVp 120 120
Iterative Level No No
AEC? No No
Typical CTDIvol (mGy) 50 50
Image Thickness (mm) 5 mm 5
NEUSOFT – TYPICAL AAPM CTWGNP PROTOCOLS
Axial Helical
Nominal Collimation 18 12
Pitch NA 0.75
kVp 120 120
Iterative Level NA NA
AEC? No No
Typical CTDIvol (mGy) 70 55
Image Thickness (mm) 4.5 5
PHILIPS – TYPICAL AAPM CTWGNP PROTOCOLS
Axial Helical
Nominal Collimation 10 40
Pitch NA 0.4
kVp 120 120
Iterative Level NA NA
AEC? No No
Typical CTDIvol (mGy) 55 55
Image Thickness (mm) 5 5
HFHS PHILIPS BRILLIANCE 64 PROTOCOLCTDIvol ~ 57 mGy, 2.5 mm Image Thickness, pitch = .671, No AEC, Collimation Width
= 40 mm
SIEMENS – TYPICAL AAPM CTWGNP PROTOCOLS
Axial Helical
Nominal Collimation 16-38 38-75
Pitch NA .55
kVp 120 120
Iterative Level No No
AEC? No No
Typical CTDIvol (mGy) 60 59
Image Thickness (mm) ~5 5
HFHS SIEMENS SENSATION 64 PROTOCOLCTDIvol ~ 55 mGy, 3 mm Image Thickness, Pitch = 0.8, No AEC, Collimation Width =
28.8 mm
TOSHIBA – TYPICAL AAPM CTWGNP PROTOCOLS
Axial Helical
Nominal Collimation 16-160 16
Pitch NA 0.65
kVp 120/135 120/135
Iterative Level
AEC? No No
Typical CTDIvol (mGy) 73/60 60
Image Thickness (mm) 4 5
HFHS* TOSHIBA AQUILION 64 PROTOCOLCTDIvol ~ 51 mGy, 5 mm Image Thickness, pitch = 0.65, No AEC, Collimation Width
= 16 cm (*Different Radiology Group than Other Systems)
NPS
ProjectionNPSFFT of ProjectionFilter –Derived from NPS
Filter * FFT of ProjectionFiltered ProjectionFiltered Projection with Bone NPS
Bone NPS
NPS OF DIFFERENT SYSTEMS
0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5
Nor
mal
ized
Rad
ial N
PS
mm-1
NPS of Different Systems and Kernels
Normalized GE StandardNPS
Normalized Philips UB NPS
Normalized Toshiba FC63NPS
Normalized Siemens H45sNPS
SUMMARY OF TYPICAL/SUGGESTED DOSESManufacturer/Organization CTDIvol (mGy)
ACR DIR Mean 57
GE 55
Hitachi 50
Neusoft 55
Philips 55
Siemens 60
Toshiba 60
AXIAL VERSUS HELICAL• Axial
• Easy to repeat a single section
• Switch kVp between cerebrum and base
• Longer acquisition time
• May get more cone beam artifacts at extremes of trans-axial coverage
• Helical
• Faster scan time possible
• Windmill artifacts in posterior fossa
• Helical over-scanning may increase total dose
• Tilt may not be available
HELICAL SCAN ISSUESPitch ~ 1.5 Pitch < 1
WHAT IS THE OPTIMAL TUBE POTENTIAL?
140 kVp 120 kVp 100 kVp
SAME DOSE – DIFFERENT KVP140 kVp 120 kVp
SAME DOSE- DIFFERENT KVP140 kVp 120 kVp
SAME PATIENT – DIFFERENT DOSE
140 kVp (103 mGy) 120 kVp (62 mGy)
SAME PATIENT DIFFERENT DOSE140 kVp 120 kVp
WHAT IS AN APPROPRIATE DOSE FOR A PEDIATRIC HEAD CT?
• ACR CT Dose Index Registry values (Jan - June 2012)• Brain w/o IV Contrast
• Mean CTDIvol (0-2 yr olds) 30 mGy
• N = 2135 exams, Std Dev 13 mGy
• Highest dose single pass in exam
0
10
20
30
40
50
60
70
80
90
CTDI vol(mGy)
0-2 3-6 7-10 11-14 15-18Sample Size (2135) (1479) (1433) (2061) (3974)
Age (yrs)
ACR CT Dose Index RegistryBrain Exam w/o IV Contrast Age Range
(years)Mean
CTDIvol(mGy)
0-2 30
3-6 36
7-10 45
11-14 49
15-18 55
PEDIATRIC HEAD CT DIR DATA JULY-DECEMBER 2012
Age Number25th
Percentile Median75th
Percentile
0-2 4243 17 26 37
3-6 2866 23 33 44
7-10 2651 28 40 50
11-14 4364 34 47 56
15-18 8238 43 52 62
PEDIATRIC PATIENTS100 kVp (12.9 mGy) 120 kVp (19.8 mGy)
ACR CT ACCREDITATION PROGRAM DOSE LIMITS• Based Solely on CTDIvol (not DLP)• Two levels:
• Reference level and Pass/Fail level
• Exam Ref Level Pass/Fail Level• Adult Head 75 mGy 80 mGy• Adult Abdomen 25 mGy 30 mGy• Pediatric (5 y/o) Abd 20 mGy 25 mGy• Pediatric (1/y/o) Head
HENRY FORD PEDIATRIC PROTOCLS
0-2 Years Old 2-18 Years Old
kVp 100 120
Image Thickness 2.5 5
CTDIvol 12.5 26
PEDIATRIC HEAD CT OPEN QUESTIONS• How many protocols and at what age/size ranges?
• Is a lower CNR acceptable given the expected imaging tasks?
• Are limited studies sufficient for repeat patients?
• How to best protect the lens of the eye?
• AAPM CTWGNP currently working on Pediatric Head protocols
Who has pediatric specific head protocols?How many age groups?
Thank You!