PACS: ERGONOMIC CONSIDERATIONS 1 - AMOS Online

21 Pages·2012·6.18 MB·English

RADIOLOGY
RESEARCH
Radiographic Tomosynthesis:
Acquisition Parameters
Michael J. Flynn, PhD
Henry Ford Health System
Detroit, MI
Learning Objectives
Learn ..
1. Appreciate the importance of scan direction ,
2. Understand how tomosynthesis (TS) images can
have better resolution than CT images
3. Learn guidelines for performing TS examinations,
.. [with muskuloskeletal examples]
M 2012
AP
A 22
A -DR & Tomosynthesis (TS)
Digital Radiography (DR)
detectors capable of rapid
sequence acquisitions are
effective for xray
TomoSynthesis (TS) imaging;
• High resolution
• No geometric
distortion
• High frame rate
(pulsed)
• Minimal lag
Accurate mechanical
movement of the detector
M 2012 aton da cxh-ireavye thuibgeh idse rteaqilu ired
AP from TS reconstruction.
A 3
PACS: ERGONOMIC
CONSIDERATIONS 1
A –Shimadzu Sonialvision / Safire
•The Shimadzu
Sonialvision / Safire
system integrates the
digital detector within a
radiographic tilt table.
•Shown in the tilt
position for a lateral
knee tomosynthesis
acquisition ( 60o), the
detector translates up
and the x-ray tube
moves downward.
• The x-ray central beam
is directed at the joint
surface with an angle
M 2012 t+h2a0t d veagrrieese sfrom -20 to
AP
A 4
A –GE VolumeRAD
• For the GE VolumeRAD system, the tube angle
APM 2012 • Tchhaen dgeeste acst othr er etmubaein ms oinu nat s mtaotvieosn alirnye paorlsyi.tion.
A 5
B.1 –Acquisition lag
•Tomosynthesis requires the
acquisition of many views
acquired as a very rapid
sequence.
•Minimal lag from frame to
frame is required
M 2012
AP
A 6
PACS: ERGONOMIC
CONSIDERATIONS 2
B.1 –Transient Response
Rapid Edge Movement Test
• 1.51 mm Cu edge
• High edge position
• Low central layer
• 74 frames
• 30 frames/second
Radiographic technique
• RQA5 ‘equivalent’
• 70 kVp, 1 mA-S
M 2012 • .5 Cu, 2 mm Al
AP
A 7
B.1 –Transient Response
Rapid Edge Movement Test
• 1.51 mm Cu edge
• High edge position
• Low central layer
• 74 frames
• 30 frames/second
Radiographic technique
• RQA5 ‘equivalent’
• 70 kVp, 1 mA-S
M 2012 • .5 Cu, 2 mm Al
AP
A 8
B.1 –Transient Response
• Edge advances
~ 1 cm per frame
• Signal measure
from the same
region for each
frame.
M 2012
AP
A 9
PACS: ERGONOMIC
CONSIDERATIONS 3
B.1 –Transient Response High to Low Transient
25000
Linear Image Value vs Time
20000
e
u
al15000
V
e
g
ma10000 0.061 of transient change
I T1/2= 2 frames (66 mS)
5000
0
0 200 400 600 800 1000 1200
M 2012 millisecs
AP
A 10
B.1 –Transient Response Low to High Transient
25000
Linear Image Values vs Time
20000
e
alu15000
e V 0.062 of transient change
mag10000 T1/2 = 1.5 frames (50 mS)
I
5000
0
0 200 400 600 800 1000
M 2012 Time [sec]
AP
A 11
B.2 -Tomosynthesis Line Response
Tomosynthesis Line Response
• Slice sensitivity
• Resolution (LSF FWHM)
M 2012
AP
A 12
PACS: ERGONOMIC
CONSIDERATIONS 4
B.2 -TS Wire Phantom • Wire test phantom
• 80 micron Tungsten
M 2012
AP 1 : 10 pitch
A 13
B.2 -TSAcquisition Response
Acquisition frame 65 kv, 1 mA-S .5 Cu filtration
10 cm height .4 mm focal spot
0 degrees
6 degrees
M 2012
AP
A 14
B.2 -TS Reconstructed Response
Tomosynthesis Reconstruction of wire phantom
• Slice intervals of 1 mm
• Well focused over 5 mm thickness
• Slice sensitivity ~ 3 mm (FWHM)
3 mm
M 2012
AP
A 15
PACS: ERGONOMIC
CONSIDERATIONS 5
B.2 -TS spatial response
SliceThickness (Sensitivity):
Peak contrast of a thin line vs height
FWHM = 3.02 mm
(rsna 2007)
M 2012
AP
A 16
B.2 -TS response
TS Resolution:
•Thin wire
response at TS reconstruction
maximum • 80 micron wire
contrast. •• C40ut doefgfr feielt earc q#u4isition
•Re-projection • 2x2 bin, 300x300 µm
with 1/10thsub-
pixels
FWHM = 0.24
mm
(rsna 2007)
M 2012
AP
A 17
B.2 -TS line response
Fourier
transform
(magnitude) of
TS reconstruction
LSF •80 micron wire
•Cutoff filter #4
•40 degree acquisition
Extended spatial •2x2 bin, 300x300 µm
frequency
response but no
low frequency,
DC, information.
M 2012
AP
A 18
PACS: ERGONOMIC
CONSIDERATIONS 6
B.3 –TS vs CT resolution
• In the x direction, TS resolution is about 3 times
better than current CT scanners.
• In the x direction, TS slice thickness about 3
time worse than thin slice CT scans.
M 2012
AP
A 19
B.3 -3D spatial frequency domain
CT
ω
Modern Multi-slice VCT z
scanners have nearly ω
y
isotropic response with
maximum spatial
frequencies of .8 to 1.0
cycles/mm
ω
x
M 2012
AP
A 20
B.3 -CT Resolution (2006 SPIE)
Clinical Multi-slice scanners
• 64 slice scanners
• GE Lightspeed VCT 64
• Siemens Sensation 32x2
• PlSF FWHM
• Transverse 1.14 +/-.05 mm
• Axial 0.87 +/-.11 mm
• 10% MTF Freq.
• Transverse 0.74 +/-.02 cycles/mm
• Axial 0.92 +/-.12 cycles/mm
For purposes of comparison, we
express typical VCT performance as;
M 2012 ••10..0803 cmymcl e s / m m ((1F0W%H MMT PFl)S F)
AP
A 21
PACS: ERGONOMIC
CONSIDERATIONS 7
B.3 -3D spatial frequency domain
TS
Tomosynthesis ωz ω
extends the y
transverse
response at the
expense of the
slice width (Z)
ω
x
M 2012
AP
A 22
B.3 -Frozen Cadaver –Tibial Plateau
standard
GE VCT Shimadzu TS
APM 2012 Nearly matched coronal planes from reformatted 3D CT (GE)
A 23
B.3 -Frozen Cadaver –Tibial Plateau
Bone+
GE VCT Shimadzu TS
M 2012 Nearly matched coronal planes from reformatted 3D CT (GE)
AP
A 24
PACS: ERGONOMIC
CONSIDERATIONS 8
B.3 -3D spatial frequency domain
• In the x direction, TS resolution is about 3 times
better than current CT scanners.
• In the x direction, TS slice thickness about 3
time worse than thin slice CT scans.
• HOWEVER,
the TS image is NOT a tomogram in that large
segments of the volumetric spatial frequency
domain are un-sampled.
M 2012
AP
A 25
B.3 -Tomosynthesis Reconstruction ωz
Frequency coefficients
Filtered Backprojection from the view acquired at
-10o.
• The reconstruction is
similar to cone beam CT but C
wanitghle a. limited acquisition A ωx
• The tomosynthesis image B
quality can be understood
from the Fourier
representation of the
acquired data.
US PAT #s 6643351, 6463116
A.High signal frequencies in the x,y directions provide in-plane detail.
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AP
A 26
B.3 -3D spatial frequency domain
TS vs CT ω
z
Unsampled frequencies ω
y
along the ωyaxis make
TS and CT
complimentary.
ω
x
M 2012
AP
A 27
PACS: ERGONOMIC
CONSIDERATIONS 9
B.3 Orientation effect
Grid phantom made from a the
grid of a fluorescent ceiling light;
• 1 cm aluminum louvers 12 cm x 12 cm
• 14 mm spacing •45oto scan
•0o/ 90oto scan
M 2012
AP
A 28
B.4 –MultipleTS views
• Because of the large slice thickness
and anisotropic spatial resolution,
multiple TS view are needed to
examine organs in different
orientations.
• This is an important distinction
relative to CT where sagital, coronal,
and transverse views are obtained
from the same acquisition.
M 2012 A1Y .Ao ZrP hM2o Vn2gi0e, 1wM2 ,CD Sh AeUsn-tdC eT-r2Ss1o8n-1
AP
A 29
B.4 –MultipleTS views
AP View 60-30 View
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A 30
PACS: ERGONOMIC
CONSIDERATIONS 10