HAPPY EASTER - Faith Lutheran Church

How to Learn MRI
An Illustrated Workbook
Exercise 12: Diffusion Weighted
Imaging (DWI)
Teaching Points:
• Learn about Diffusion weighted imaging
and how to produce these images.
• Learn about Post-Processing Analysis of
Diffusion weighted images.
1
Fig 12.1 Head coil
Step 1: Preparing the head coil
Place the 8-Channel head coil on the table, and put a
cushion pad in the coil and a sanitary sheet on top of
it.
Step 2: Positioning the
volunteer
Place the volunteer on a head-first position, which
means that the coil base should be close to the
magnet bore (Fig 12.2). Cover him/her with a blanket,
remember the ear plugs and squeeze-ball, and put
a cushion under the knees to relieve back pressure.
Sometimes we use medical tape to immobilize the
head further (See fig 12.3).
Fig 12.2 Friend’s Head in coil
Step 3: Landmark the Brain
Landmark at the superior edge of eyebrows.
Fig 12.3 Tape Technique (Note: You can also tape the chin for even better
prevention of motion.)
2
Step 4: Three Plane Localizer
Click New Series in Rx Manager, select INRX, and then click View Edit. Set the parameters (Fig 12.4). Check
if the coil type is 8 Channel Head Coil. Click Save series, Download, Prep Scan, and then Scan.
Fig 12.4 3 Plane localizer parameter
Patient Information
Patient Protocols
Site
Accession 0000
Number
Patient
Position
Head
Patient ID 0000
Patient
Entry
Head First
Coil
8HRBRAIN
Neck/Cervical
Patient Name
Chest Thoracic
Upper Extremities
Auto Start
Supine
Series
Description
3-plane localizer
Abodomen/Lumbar
Plane
3-Plane
Mode 2D
Fiesta
Grad
Mode
Pelvis
LowerExtremities
Imaging
Options
Other
Protocol
Min.
Max
1.0
2.0
Aquisition Timing
Graphic RX
OFF
Phase 128
Flow Comp
Direction
NEX 1.00
Shim
Image
Users CVs
Enhance
Screen
1.4
1.4
TE2
0.0
0.0
Phase
FOV
TR
5.0
5.0
Acqs Before
Pause
Inv. Time
0
0
TI2
0
0
30
30
Echo Train
Length
31.2
31.2
Bandwidth2
31.2
31.2
Auto
Phase Correct
1.00
Contrast
ml
Amf
Agent
Scanning Range
FOV
Bandwidth
Freq DIR Unswap
Freq 256
TE
Flip Angle
HIS/RIS
Protocol
Additional Parameters
Scan Timing
Seq, Fast
Psd Name
Full
Info
# of TE(s)
per scan 1
Pulse Seq
Slice
Thickness:
30.0
5.0
Min.
Max
5
48
S/I
A/P
R/L
Center
0.0
0.0
0.0
Spacing
2.5
2.5
2.5
# Slices:
1
1
1
Table
Delta
0.00
3
Step 5: Asset Calibration
Copy and Paste 3 Plane loc on your Rx Manager then click View Edit. Set your parameters and fill up the
Patient Position, Imaging Parameters, Acquisition Timing, and Scan Timing (Fig 12.5). Click Graphic Rx
and be sure to prescribe enough slices to cover the whole brain. Click Save Series, Download, Prep Scan,
and then click Scan.
Fig 12.5 Calibration sequence parameter
Patient Information
Patient Protocols
Site
Accession 0000
Number
Patient
Position
Head
Patient ID 0000
Patient
Entry
Head First
Coil
8HRBRAIN
Neck/Cervical
Patient Name
Chest Thoracic
Upper Extremities
Auto Start
Supine
Series
Description
Calibration Scan
Abodomen/Lumbar
Plane
Axial
Mode Calib
gradient Echo
Grad
Mode
Pelvis
LowerExtremities
Imaging
Options
Other
Protocol
TE
Min.
Max
1.0
2.0
1.5
1.5
TE2
1.0
1.0
TR
3.2
6000.0
0
100000
50
4000
1
90
Inv. Time
TI2
Flip Angle
Echo Train
Length
Bandwidth
Bandwidth2
0.0
31.2
31.2
Aquisition Timing
Freq DIR AVP
Freq
Graphic RX
OFF
Phase
Flow Comp
Direction
NEX
Shim
Image
Users CVs
Enhance
Screen
Auto
Phase Correct
Phase
FOV
Contrast
Acqs Before
Pause
ml
Amf
Agent
Scanning Range
FOV
31.2
HIS/RIS
Protocol
Additional Parameters
Scan Timing
Fast Calib
Psd Name
Full
Info
# of TE(s)
per scan 1
Pulse Seq
Slice
Thickness:
Spacing
36.0
5.0
Min.
Max
5
48
S/I
Start
I110.0
End
S100.0
# of 41
Slices:
Actual
End S100.0
R/L
0.0
A/P
0.0
Table
Delta
0.00
4
Diffusion Weighted Imaging (DWI)
Diffusion Weighted MRI provides image contrast that is dependent on the molecular motion of
water, which may be altered by disease. It reduces the MR signal due to the diffusion of water
molecules along a field gradient. The use of bipolar strong gradient pulses and suitable pulse
sequences allows the acquisition of diffusion weighted images. If there’s no net movement, the
first pulse dephases the spins, and the second pulse rephrases the spins. Signal attenuation occurs
if there’s a net movement of spins between the gradient pulses. Watery tissues that have mobile
molecules give lower signal intensity and the display from this area is brighter, while more solid and
static tissues give a stronger signal. The degree of diffusion weighting is determined by the strength
of the diffusion gradients, duration of the gradients, and the time between the gradient pulses.
Diffusion weighted imaging is an important method in the assessment and diagnosis of acute
brain infarction and in the differentiation of acute infarction from other disease processes. Area of
acute ischemia can be separated from old strokes and other chronic changes in the brain. Acute
infarcts appear hyperintense, while subacute and chronic infarcts, vasogenic edema, punctuate and
confluent changes of deep white matter ischemia are not bright.
Step 5: Diffusion-weighted Imaging (DWI)
Copy and Paste 3 Plane loc on your Rx Manager then click View Edit. Set your parameters (Fig
12.6a). Click the DWI Screen under Additional Parameters and set the Diffusion Option parameters
(Fig 12.6b). Go to Graphic Rx and adjust the localizer to 3 slices (Fig 12.7). Click Save Series,
Download, Prep Scan, and then click Scan.
5
Fig 12.6 AXL DWI parameter
(a) Set the parameters
Patient Information
Patient Protocols
Site
Accession 0000
Number
Patient
Position
Head
Patient ID 0000
Supine
Patient
Entry
Head First
Coil
8HRBRAIN
Neck/Cervical
Patient Name
Chest Thoracic
Series
Description
Upper Extremities
Auto Start
AXL DWI
Abodomen/Lumbar
Plane
Oblique
Mode 2D
Spin Echo
Grad
Mode
Pelvis
Pulse Seq
LowerExtremities
Imaging
Options
Other
Protocol
Psd Name
Full
Info
Min.
Aquisition Timing
Max
Minimum
TE2
TR
8000.0
99.8
99.8
20.0
2000.0
50
4000
TI2
50
4000
1
180
Flip Angle
Echo Train
Length
Bandwidth
Bandwidth2
Graphic RX
OFF
0.0
250.0
250.0
Shim
1.00
Contrast
Locs Before
Pause
2.00 Ph
Auto
Phase Correct
ml
Amf
Agent
Scanning Range
FOV
62.5
NEX 1.00
Phase
FOV
ASSET
DWI
Screen
Phase 128
Flow Comp
Direction
Image
Users CVs
Enhance
Screen
1000.0 17000.0
Inv. Time
Freq DIR R/L
Freq 128
# of Shots 1
TE
HIS/RIS
Protocol
Additional Parameters
Scan Timing
EPI, DIFF, Asset
Slice
Thickness:
Spacing
22.0
Min.
Max
8
60
5.0
R/L
L13.9
A27.1
I78.5
End
L13.9
A26.6
S101.5
# of
Slices:
0.0
8.0
A/P
S/I
Start
27
Table
Delta
0.00
(b) Diffusion Option window
b-Value 1000
Direction
Directions
ALL
3
# of T2 Images 1
Recon All
Images
ADC
Accept
Optimize TE
Fractional Aniso
!"#$%&'()
*+,-
Combined
6
Fig 12.7 Graphic Rx for DWI sequence
Graphic Rx
X
Erase Selected
Erase All
Reset
Center
Fallback
to SO
Loc Ref
Lines
Report
Cursor
Update All
Keep W/L
2
3
1
3
1
2
Display
Normal
1.0
ZOOM
Copy Rx...
Select Series
Select image
...
SAT
*
Graphic Rx
Scan Plane: Oblique
FOV: 22.0
Localized image - 1, 3
Phase FOV 1.0
Accel.
Bar:
Fat
Slice
5.0
Thickness:
Fat Classic
0.0
Spacing
SPECIAL
Water
Freq DIR: R/L
Shim FOV:
locs Before
Pause:
Shime Vol
TR: 8000.0
Minimum TR: 1000.0
Hide Shim
Start:
R7.3
P0.2
S17.1
End:
R7.3
P0.2
S22.1
# of
Slices
3
Fig 12.8 Diffusion Weighted Images
!
Step 6: Clean up
!
7
Step 7: Diffusion Post-processing
On the MR computer console, go to the browser list, click your volunteer’s name, click the AXL DWI
sequence, and then click Functool (fig 12.9).
Fig 12.9 Browser list
.''$(+#:(-)T% &8$8+:(-)T%
C8>-78
&-6:T% K8:9-6U%
.6+,(78T% <<&
V"8"8
*;#>()#:(-)?%T%
Exam
| Name
4238/MR55| MR PLASTIC
W:($(:(8?
&867(+8?%
@8??#B8?
*;#>%)-%MFENO%@[email protected]%<S.&542
| Date
Ser
| Description | Mod| PPS | A |
| Mar 04 09 | QA
| MR | -
1
3
4
5
6
7
8+C
9+C
10+C
11+C
98+C
500
501
| N |
| Type
| Imgs
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PROSP
PROSP
PROSP
PROSP
PROSP
PROSP
PROSP
PROSP
PROSP
PROSP
SSAVE
PROC
PROC
3
23
30
60
24
16
16
24
30
20
1
30
30
3 PLANE LO
SAG T1
AXL FLAIR
AXL DWI
COR T2 FS
AXL T1 ORB
AXL T1 FS
COR T1 FS
AXL T1 +C
COR T1 FS
Exam/Serie
Exponentia
Apparent D
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MR
MR
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GEMS
GEMS
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GEMS
GEMS
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E!
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GLE%8;#>()#:(-)?
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Img
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Loc | Flip | Echo |
TE |
(mm)| (deg)|
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S100.0 |
60 | 1/1 | 1.528 |
S 93.5 |
60 | 1/1 | 1.528 |
S 87.0 |
60 | 1/1 | 1.528 |
S 80.5 |
60 | 1/1 | 1.528 |
S 74.0 |
60 | 1/1 | 1.528 |
S 67.5 |
60 | 1/1 | 1.528 |
S 61.0 |
60 | 1/1 | 1.528 |
S 54.5 |
60 | 1/1 | 1.528 |
S 48.0 |
60 | 1/1 | 1.528 |
S 41.5 |
60 | 1/1 | 1.528 |
S 35.0 |
60 | 1/1 | 1.528 |
S 28.5 |
60 | 1/1 | 1.528 |
=($>%2->'-?86
=")+:--$
TI |
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TR
(ms)
160
160
160
160
160
160
160
160
160
160
160
160
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TDEL
(ms)
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Thck/Sp
(mm)
5.0/ 0.0
5.0/ 0.0
5.0/ 0.0
5.0/ 0.0
5.0/ 0.0
5.0/ 0.0
5.0/ 0.0
5.0/ 0.0
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5.0/ 0.0
5.0/ 0.0
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FOV
(cm)
22x22
22x22
22x22
22x22
22x22
22x22
22x22
22x22
22x22
22x22
22x22
22x22
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Matrix | NEX
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128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
128x128 | 2.00
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434
@()(%3(8986
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<6-:-2-'A
<6-:-*;+,#)B8
C8D-6>#:
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EF%(>#B8?
Click ADC to display the Processing Threshold pop-up window (Fig 12.10a). Adjust the Right Slider all the
way to the right, and the Left slider just a little close to the maximum level (Fig 12.10b). Notice that the
brain image (Fig 12.10c) will be highlighted in green, representing the pixels within the selected range
of values you selected. By setting the left slider only close to the maximum means the range will just be
within the perimeter of the brain.
8
Fig 12.10 Processing Thresholds
605270 left @ 256 2
185786 left @ 5122
March 4
7:23 PM
Disk 32% full
The patient comfort level has
returned to normal
Idle
iLinq
4237/4/26
28/28
Sent: 4236/10
(DYNACAD61)
Removed
Series 4234/9
Functional 5.2.07
New
Protocol
ADC
ADC -Step 3/3
___ ___
__ ___
___
Processing Thresholds
•
Set sliders to select range of MR Units to be
processed.
Pixels within the selected range of values ae shown in
green
aA
357
16415
Noise
Upper
Pref./
Settings
Film/Save/
Report
Close
Back
1/3
Next
Click Next to go the B-values window. The B-value is the degree of diffusion sensitivity. On the
example given below, B-value is set to 1,000 s/mm2 (Fig 12.11). Click Next again to display the Final
Settings window.
Fig 12.11 B Values
___ ___
__ ___
___
ADC -Step 3/3
B Values
aA
1000 0 - - -
Pref./
Settings
Film/Save/
Report
Close
Back
2/3
Next
9
Click Compute and then click Close (Fig 12.12a). Go to Film/Save/Report and choose Functional Maps
(Fig 12.12b).
Fig 12.12 Final Settings
(a) Compute
(b) Functional Maps
___ ___
__ ___
___
ADC -Step 3/3
Film/Save/
Report
Final Settings
1000 0- - Noise 357
Upper 16415
b-values
Threshold
aA
Advanced
Settings
Film
Composer
Series
Data
Graph
Data
Compute
Functional
Maps
Pref./
Settings
Generate
Report
Film/Save/
Report
3/3
Next
Select All for the Functional Map(s) and then select Multiple locations (Fig 12.13). Click Next to display the
Film/Save Format window.
Fig 12.13 Film/Save Functional Maps
Film/Save Functional Map(s)
Film/Save Functional Map (s)
Select functional map (s)
Visible
maps
Left
Select from available maps...
Select single or multiple location (s)
Single location
Close
Save
Multiple locations
Back
Next
10
Choose Save as processed images (F) then click Save (Fig 12.14).
Fig 12.14 Film/Save Format
___ ___
__ ___
___
Film / Save Functional Map (s)
Film / Save Format
Select format
Send to Film Composer (F1)
Save as SCREENSAVE image (S)
SCREENSAVE + Add To Report
Save as processed images (F)
(PROCESS / REFORMAT / SCPT)
aA
Research
Save as TIFF on
Hard Disk
Floppy Disk
Pref./
Settings
Film/Save/
Report
CloseB
ack
Next
Fig 12.15 Signal Intensity of the Diffusion Data
To get the signal
intensity of a
particularly area of
the brain, place the
cursor on the area
to display the signal
intensity graph
(signal intensity vs
B-value). Compare it
to the same area of
the other side of the
brain.
11
In acute cerebral ischemia, the cerebral blood flow is reduced and there’s failure of the cell membrane
ion pump. Excess sodium enters the cell, followed by a net movement of water from the extracellular to
intracellular compartment causing edema. There will be a decreased ADC due to the restricted diffusion,
causing an increased signal intensity on diffusion-weighted images.
Fig 12.16 Maps of the Apparent Diffusion Coefficient
605270 left @ 256 2
185786 left @ 5122
March 4
7:23 PM
Disk 32% full
The patient comfort level has
returned to normal
Idle
iLinq
4237/4/26
28/28
Sent: 4236/10
(DYNACAD61)
Removed
Series 4234/9
Functional 5.2.07
New
Protocol
ADC
ADC -Step 3/3
___ ___
__ ___
___
aA
Pref./
Settings
Film/Save/
Report
Close
Back
1/3
Next
The Apparent Diffusion Coefficient (ADC) determines the diffusion coefficient calculated for each voxel.
The ADC map is the pixel-by-pixel display of all diffusion coefficients. It is acquired via post-processing by
calculating the ADC for each voxel of tissue and allocating signal intensity according to its value. The map
is needed to standardize the data and to obtain quantitative information from diffusion-weighted images.
Damaged tissues have restricted diffusion, so they have low ADC and appear dark, while normal tissues
with free diffusing area have high ADC and appear bright.
12
Suggested Readings:
http://radiology.rsna.org/content/217/2/331.full
http://spinwarp.ucsd.edu/NeuroWeb/Text/br-710dwi.htm
http://www.ncbi.nlm.nih.gov/pubmed/15775887?ordinalpos=1&itool=EntrezSystem2.PEntrez.
Pubmed.Pubmed_ResultsPanel.Pubmed_SingleItemSupl.Pubmed_Discovery_RA&linkpos=1&log$
=relatedreviews&logdbfrom=pubmed
http://bjr.birjournals.org/cgi/content/full/77/suppl_2/S176
http://www.ajnr.org/cgi/reprint/20/7/1193.pdf
http://books.google.com/books?id=PZoaJek9u-oC&pg=PA375&lpg=PA375&dq=post+processing+
ADC+maps&source=bl&ots=ihHcm7JsjN&sig=WUe-u072-vIOTiqeScu1uOTjHRU&hl=en&ei=sfRVS4
uxCNLL8Qbbz92qBA&sa=X&oi=book_result&ct=result&resnum=7&ved=0CCEQ6AEwBjgK#v=onep
age&q=post%20processing%20ADC%20maps&f=false
`