centre of rotation is there a problem in the y dimension n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Centre of Rotation: Is there a problem in the Y dimension? PowerPoint Presentation
Download Presentation
Centre of Rotation: Is there a problem in the Y dimension?

Loading in 2 Seconds...

play fullscreen
1 / 31

Centre of Rotation: Is there a problem in the Y dimension? - PowerPoint PPT Presentation


  • 84 Views
  • Uploaded on

Centre of Rotation: Is there a problem in the Y dimension?. Stephen Brown - Southend Mike Avison - Bradford. Tc99m point source positioned on-axis In the ideal situation the source would appear in the central pixel in both heads. Y axis. Tc99m point source positioned on-axis.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Centre of Rotation: Is there a problem in the Y dimension?' - owena


Download Now An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
centre of rotation is there a problem in the y dimension

Centre of Rotation:Is there a problem in the Y dimension?

Stephen Brown - Southend

Mike Avison - Bradford

slide2

Tc99m point source positioned on-axis

In the ideal situation the source would appear in the central pixel in both heads

Y axis

slide3

Tc99m point source positioned on-axis

-the problem of sag (affects y alignment)

Y axis

slide4

Y axis

Y error should be proportional to radius

slide5

Y axis

Sometimes we used the 3 point IRC source

Y error on rear source is less than front source

-the radii are more similar for rear source

how did we measure irc y error
How did we measure IRC Y error
  • Acquire dual head 360° of data (point source)
  • Use Display A - FWHM
    • Place ROI over point, read Y centroid
    • Enter data in spread sheet
  • Interfile Export to Park
    • Automatic processing checks X too
  • Odyssey IRC test
    • gives misleading and ill defined results
how did we measure irc y error1
How did we measure IRC Y error
  • Acquire dual head 360° of data (point source)
  • Use Display A - FWHM
    • Place ROI over point, read Y centroid
    • Enter data in spread sheet
  • Interfile Export to Park independent computer
    • Automatic processing checks X too
  • Odyssey IRC test
    • gives misleading and ill defined results
how did we measure irc y error2
How did we measure IRC Y error?
  • Acquire dual head 360° of data (point source)
  • Use Display A - FWHM
    • Place ROI over point, read Y centroid
    • Enter data in spread sheet
  • Interfile Export to Park
    • Automatic processing checks X too
  • Odyssey IRC test
    • gives misleading and ill defined results
slide13

Ref.

Ref.

<1.0

<0.5

<0.5

<1.0

<0.65

<1.5

Is this X or Y or a combination of both?

It’s a long way from 5mm so what does it mean?

I think I was !!!

results heads at max radius 38 6 cm
Results(heads at max radius 38.6 cm)

Camera (collimator) Maximum Y deviation (mm)

Front Mid Rear

Axis Southend (LEHR) 7.7 5.5 3.6

Axis 1 BRI (LEGP) 5.0

Axis 2 BRI (LEHR) 7.4 5.3 5.2

Axis 1 BRI (MEGP) 7.6 7.1 7.1

mean = 5.7

Acceptance criteria: typically 1 or 2mm maximum Y deviation

is 5 mm too big
Is 5 mm too big?
  • We are hoping to resolve objects of about 10mm in SPECT of trunk sized volumes
  • What resolution do we aspire to for DAT scan?
  • Guidance from professional bodies state
    • 1mm or 2mm (range) as acceptable
  • How do other gamma cameras perform?
is this bad performance

Is this bad performance?

Comparison with other brands of camera

results by brand le collimators
Results - by brand (LE collimators)

Camera Max Y deviation (mm) Radius cm

Axis (avg) 5.7 38

E Cam 3.1 33

Hawkeye 1.7 33

Argus 4.8 (single head) 33

Forte A 5.4 34

Forte B 5.4 34

results by brand normalised normalised to 33cm radius le collimators
Results - by brand: NormalisedNormalised to 33cm radius (LE collimators)

Camera Max Y deviation (mm)

Axis (avg) 5.0

E Cam 3.1

Hawkeye 1.7

Argus 4.8 (single head)

Forte A 5.2

Forte B 5.2

slide20

word of warning ...

We tested with source on axis

Symmetrical constant misalignment (not sag).

As the gantry rotates, y-centroids remain fixed therefore no error detected

Y axis

slide21

Y axis

Tc99m point source positioned off-axis

  • Source off centre in Y vertical direction
  • as the gantry rotates, y-centroids on each detector move
  • therefore the error is detected
general causes of cor errors
General Causes of COR errors
  • Misalignment of electronic and physical axis. (Electronic might change with angle)
  • Sag of detectors (Physical change with angle)
  • Detector misalignment
  • Collimators not fixed firmly
  • Collimators warp under gravity
  • Non-linearity
what should we be testing
What should we be testing?
  • Maybe …
    • acquisition of IRC jig 10cm lat. from iso-centre
    • radius 33cm
    • dual head
      • 180°
      • 102° non-circular orbit
  • Write macro to do analysis (X and Y errors)
  • When you get home try the display A method for Y errors only
summary 1
Summary 1
  • If you are using Odyssey IRC test you are probably being misled into believing performance is much better than it really is.
  • Philips should supply better documentation.
summary 2
Summary 2
  • Philips should improve correction:
    • Forte and Axis. (Worst in class).
  • Our measurements indicate:
    • If Philips modified the IRC cal. so that it took mean Y offsets for both heads over 360° and used the means to correct data, then offset errors could be reduced to 2.1 mm (Axis)
    • If Philips derived a variable correction as a function radius and angle: error could be eliminated at COR but linearly increase with radius (to 2.1 mm at 33cm)
    • This would probably meet all aspirations.
  • Further improvement would require gantry re-engineering
slide26

Axis 1

X centroids

raw

fitted

Y centroids

raw

mean

X error

Y error

slide27

Axis 2

X centroids

raw

fitted

Y centroids

raw

mean

X error

Y error

slide28

ECam

X centroids

raw

fitted

Y centroids

raw

mean

X error

Y error

slide29

Hawkeye

X centroids

raw

fitted

Y centroids

raw

mean

X error

Y error

slide30

Forte A

X centroids

raw

fitted

Y centroids

raw

mean

X error

Y error

slide31

Forte B

X centroids

raw

fitted

Y centroids

raw

mean

X error

Y error