circular versus contour orbits for brain spect imaging

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Robert Miner BSc (MRS) Nuclear Medicine Technology

Undergraduate research thesis Research Methods II (Winter 2008)

Circular versus contour orbits for brain SPECT imaging

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Circular versus contour orbits for brain SPECT imaging

Primary objective Determine whether a circular or a contour orbit produces better diagnostic quality images for brain SPECT imaging.

Hypothesis The contour orbit will give better diagnostic quality images.

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Why is this investigation justified? No papers could be found explicitly evaluating circular versus contour orbits for brain SPECT imaging. The advantages and disadvantages of circular or contour orbits for brain SPECT acquisition using LEHR collimators have not been fully investigated in the department.

Background - Literature review

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SPECT cardiac imaging was simulated by Sholberg and Watabe.They evaluated circular and contour orbits with resolution recovery software. Even though their paper dealt with software simulation of heart imaging, some concepts can be applied to brain imaging.


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Contour orbits allow the gamma camera system to get closer to the patient. The further away the camera is from the patient, the poorer is the resolution.

Source to collimator distance

Normalized collimator resolution

0 0

High resolution (LEHR)

Diagram adapted from: Cherry, et al (2003). Physics in Nuclear Medicine. (pp. 243, 247)


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References seemed to conflict in their recommendation of circular or contour orbits for brain imaging:

Ziessman and Wilson recommend keeping the collimator to patient (head) distance at a minimum, yet recommend a circular orbit. Hamilton, Christian et al and Cherry et al recommend a contour orbit for SPECT but don’t specifically mention it for brain imaging.


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Ethical issues

There are no ethical issues:

No patients or patient data are used. Standard safe handling practices of radioisotopes reduce exposure and other hazards to nuclear energy workers and students.

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A 3 dimensional Hoffman brain phantom was imaged on a dual head e.cam® gamma camera system using current brain protocol parameters.

Materials and methodology

To best solve the question only one parameter was changed: The orbit type.

e.cam is a registered trademark of Siemens Corporation.

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The Hoffman brain phantom provides a 3-D simulation of radioisotope distribution in a normal brain. It can be used for SPECT, PET and MRI imaging.

Photo from: Hoffman 3-D Brain Phantom™ data sheet (2007).


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Why use a Hoffman brain phantom?

Benefits of using a brain phantom: •  Representative of the organ. •  Can be used for subjective image analysis by doctors.

Disadvantages of using a brain phantom:

•  Dimensions may be hard to determine.


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The current dual head e.cam® gamma camera system was used to perform the scans.


Hoffman phantom

Foam tube to simulate shoulders

e.cam is a registered trademark of Siemens Corporation.

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The phantom was scanned 6 times for each orbit over 3 separate scanning sessions.

For each orbit measure: 1) Contrast 2) Physical dimensions 3) BRASS asymmetry

Phantom and 44 cm shoulders on headrest.

Circular

Contour

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Data collection and analysis

Hermes is a software package used to process images. BRASS is a specific Hermes application used for analyzing brain images. This tool generates information for 46 regions of the brain. Due to decay, each scan will have a different count profile. This limits the usefulness of some of the data generated by BRASS.

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Hermes image analysis software was used to establish line profiles that were used to calculate dimensions and contrast. The 50% level of leading edges were used to measure dimensions. Adjacent high and low activity values were used to calculate contrast.

Levels for dimensions

Levels for contrast


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Brain analysis software (BRASS, Hermes Medical Solutions) was used to analyzing the images. Images were reoriented to fit a normal template. For each image, estimates of the asymmetry between the left and right hemispheres were automatically calculated for 20 regions. Asymmetry was defined as: Asymmetry = (Left - Right) / Maximum (Left, Right)


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Dimensional measurements on 2 separate slices: 1) Outside dimensions (A/P and L/R). 2) Internal dimensions. Contrast measurements on 2 separate slices: 1) Outer A/P and L/R regions. 2) Internal regions. Contrast is defined as (High - Low)/High


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Statistical tests to analyze data

For each of the 6 measurements statistics describing central tendency and dispersion are:

•  Mean •  Standard deviation

Dimensional measurements were compared to the actual physical measurements.

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Statistical tests to analyze data

A t-Test for the directional hypothesis (the contrast for contour orbits are better) was conducted using α = 0.05. Why the t-Test?

•  The sample size is less than 30 meaning the distribution of sample means is not a normal, but rather a t-distribution.

•  The data is of a ratio scale. A significance level p = α/n was used to determine if contour orbits were significantly better for the BRASS asymmetry metric.

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Results - Outside dimensions

Lateral (R/L) Slice 33 (mm)

Contour 123.4 +/- 1.4 Circular 124.9 +/- 0.5 Actual 122.0 +/- 0.5

A

Slice 33 P

LR

Lateral (L/R) slice 33

121

122

123

124

125

126

Actual Contour Circular

Dim

en

sio

n (

mm

)

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A/P Slice 33 (mm)


A

Slice 33 P

LR

A/P slice 33

140

145

150

155

160


Dim

en

sio

n (

mm

)

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Lateral (R/L) Slice 21 (mm)


Slice 21 Lateral (R/L) slice 21

111

112

113

114

115

116

117

118


Dim

en

sio

n (

mm

)

A

R

P

L

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A/P Slice 21 (mm)


A

R

P

L

A/P slice 21

117

122

127

132

137


Dim

en

sio

n (

mm

)

Slice 21

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Results - Inside dimensions

Anterior peak Slice 21 (mm)


A

R

P

L

Slice 21 Anterior peak, slice 21

30

31

32

33

34

35

36


Dim

ensi

on (m

m)

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Results - Inside dimensions

Anterior void Slice 21 (mm)


Anterior void slice 21

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30

31

32

33

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35

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Dim

en

sio

n (

mm

)

A

R

P

L

Slice 21

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Results - Contrast

A A/P

R

Slice 33

L Lateral R Lateral

P

A

L

A/P R Lateral L Lateral Mean Mean Mean

Circular 0.62 +/- 0.02 0.42 +/- 0.05 0.31 +/- 0.08 Contour *0.67 +/- 0.03 0.45 +/- 0.05 0.31 +/- 0.18 * - Contour contrast is significantly better (p < 0.05).

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Results - Contrast

Outer Inner L Ant. Mean Mean Mean

Circular 0.70 +/- 0.06 0.68 +/- 0.06 0.19 +/- 0.06 Contour *0.78 +/- 0.02 0.73 +/- 0.04 *0.29 +/- 0.09 * - Contour contrast is significantly better (p < 0.05).

A

R

Slice 21

Outer Inner

L Ant. P

L

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Results - BRASS asymmetry analysis

Circular V/S Contour orbitsThe circular orbit is considered the control group.

Region Region Name p t Contour number critical actual significantly

better?1 L cerebellar ctx 0.002 0.037 no3 L cerebellar white matter 0.002 0.020 no5 L nucleus lentiformis 0.002 0.237 no7 L nucleus caudatus 0.002 0.063 no9 L thalamus 0.002 0.099 no

11 L sensorimotor ctx 0.002 0.298 no13 L occipital ctx 0.002 0.302 no15 L sup parietal lobule 0.002 0.258 no17 L ant dorsal frontal ctx 0.002 0.130 no19 L post dorsal frontal ctx 0.002 0.456 no21 L ant orbital frontal ctx 0.002 0.085 no23 L post orbital ctx 0.002 0.291 no25 L parieto-temporal ctx 0.002 0.356 no27 L medial temporal lobe 0.002 0.467 no29 L lateral temporal lobe 0.002 0.327 no31 L post temporal lobe 0.002 0.303 no33 L temporal pole 0.002 0.045 no35 L insular ctx 0.002 0.388 no37 L ant gyrus cinguli 0.002 0.215 no39 L post gyrus cinguli 0.002 0.010 no41 Pons and midbrain 0.002 0.060 no42 L ant subcortical 0.002 0.392 no44 L post subcortical 0.002 0.388 no46 Other subcortical 0.002 0.028 no

Contour orbit parameters significantly better than circular orbit: 00.0%

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0.02.04.06.08.0

10.012.014.016.018.020.0

Cerebe

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tx

Cerebe

llar w

hite m

atter

Nucleu

s len

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is

Nucleu

s cau

datus

Thalam

us

Senso

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r ctx

Occipi

tal ct

x

Sup pa

rietal

lobu

le

Ant do

rsal fr

ontal

ctx

Post d

orsal

fronta

l ctx

Ant orb

ital fr

ontal

ctx

Post o

rbital

ctx

Parieto

-tempo

ral ct

x

Medial

tempo

ral lo

be

Later

al tem

poral

lobe

Post te

mporal

lobe

Tempo

ral po

le

Insula

r ctx

Ant gy

rus ci

nguli

Post g

yrus c

inguli

Pons a

nd m

idbrai

n

Ant su

bcort

ical

Post s

ubco

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Other s

ubco

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ASYM

MET

RY

(%)

Circular orbitsContour orbits

Results - BRASS asymmetry analysis

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Summary - Dimensions

Circular and contour dimensional measurements were very close to each other. This indicates no significant distortion is caused by the use of contour orbits.

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Summary - Contrast

Contour contrast measurements were significantly better for 3 out of the 6 regions measured. This indicates an improvement in contrast for the contour orbit.

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Summary - BRASS Asymmetry

The contour values were no different than circular values for all of the regions evaluated. This indicates no significant difference between the circular and contour orbits for the BRASS asymmetry parameter.

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Summary

When compared to circular orbits, contour orbits showed improved contrast without causing any changes in dimensions or any distortion in the defined brain regions.

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Summary

These results are consistent with other studies: •  Sohlberg and Watabe (2006) evaluated circular and

contour orbits for cardiac SPECT imaging. Their paper demonstrated that noncircular orbits improved resolution and contrast for heart SPECT imaging.

•  Gottschalk et al (1983) demonstrated that a contour orbit improved resolution and contrast.

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Limitations encountered: •  Phantom filling issues: small bubbles that do not

dissipate. These may adversely affect BRASS values. •  The correlation of the reconstructed slice to the

physical slice in the phantom is difficult. •  Hermes only allows line regions on the X-Y axis.

Oblique line regions are not allowed.

Summary

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Other SPECT camera systems using similar cameras, collimators and reconstruction tools would be expected to show similar improvements using contour orbits for brain imaging.

Can the results be generalized? Yes

Summary

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Future Direction

The next phase would be to visually evaluate the images. A follow-up study could have physicians critique the images using a multi level scale ranging from poor to excellent.

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References

Cherry, S., Sorenson, J., Phelps, M., (2003). Physics in nuclear medicine. (3rd ed.) Philadelphia, Pa., Saunders. Christian, E. Paul, Bernier, R. Donald, Langan K. James, (2004). Nuclear medicine and PET. (5thed.). St. Louis, Missouri. Mosby. Dinbelg (2005). Body dimensions of the Belgian population. Retrieved Oct. 22 2007 from: http://www.dinbel.be/adultstotal.htm on 2997.09.22 Early P., Sodee, D., (1995) Principles and practice of nuclear medicine (2nd ed.) St. Louis, Missouri. Mosby. Germano G., (2001). Technical aspects of myocardial imaging. Journal of Nuclear Medicine, Volume 42, 1499–1507.

Gottschalk, S., Salem, D., Lim, C., Wake R., (1983). SPECT resolution and uniformity improvements by noncircular orbit. Journal of Nuclear Medicine, Volume 24, 822–828 Groch, M., Erwin, W., (2000). SPECT in the year 2000: Basic principles. Journal of Nuclear Medicine, Volume 28, number 4, 233–243.

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Hamilton, D., (2004). Diagnostic nuclear medicine a physics perspective. New York. Springer. Heertum, R., Tikofsky, R., (2000) Functional cerebral SPECT and PET imaging. Philadelphia, PA: Lippincott Williams & Wilkins. Hermes (2002). Data analysis applications. Brain Analysis (BRASS) Handbook. Kent, UK: Nuclear Diagnostics. Hermes (2001) Image display applications. Brain Analysis (BRASS). Kent, UK: Nuclear Diagnostics. Hoffman 3-D Brain Phantom™ data sheet. Retrieved from, on 27 Oct 2007 http://www.spect.com/pub/Hoffman_3D_Phantom.pdf Hoffman 3-D Brain Phantom™ data sheet and pricing. Retrieved from, on 27 Oct 2007 http://www.biodex.com/radio/phantoms/phantoms_790.htm Juni, J., et al (1999). SNM Guideline for brain Profusion SPECT using Tc-99m radiopharmaceuticals . SNM. Reston, VA.

References

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Madsen, M., (2007). Recent advances in SPECT imaging. Journal of Nuclear Medicine, Volume 48, number 4, 661–673. Polgar, S., Thomas, S., (2000) Introduction to research in the health sciences. New York, NY: Elsevier Curchill Livingstone. Sohlberg, A., Watabe, H., (2006). Body-contour acquisition versus circular orbit acquisition with resolution recovery in cardiac SPECT. IEEE Nuclear Science Symposium Conference record. M14-306 TOH (2006). Brain perfusion study. The Ottawa Hospital Nuclear Medicine Civic campus. Ottawa. TMI (2006). RMRD240 Research methods 1. Hypothesis testing. March 19th class handouts.

References

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Vines, D., Ichise M., (1999). Evaluation of differential magnification during brain SPECT acquisition. Journal of Nuclear Medicine, Volume 27, 198–203. Wernick, M., Aarsvold, J., (2004) Emission tomography The fundamentals of PET and SPECT. Philadelphia, PA: Lippincott-Raven. Wilson, A. Micheal (1998) Textbook of nuclear medicine. San Diego, California: Elsevier Academic press. Ziessman, A. Harvey, O’Malley, P. Janis, Thrall, H. James (2006) The requisites nuclear medicine (3rd ed.) Philadelphia, PA: Elsevier Mosby.

References

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Clinical Contacts

My research mentor:Dr. Richard Wassenaar, Ph.D.Medical Physicist, Division of Nuclear MedicineOttawa Hospital-Civic Campus1053 Carling Ave., Ottawa K1Y 4E9 (613) 798 5555 [email protected]

My clinical supervisor:Blair Ziebarth M.R.T.(N.)Clinical Teaching CoordinatorNuclear MedicineOttawa Hospital-Civic Campus1053 Carling Ave., Ottawa K1Y 4E9(613) 798 5555 [email protected]

Student:Robert MinerNuclear Medicine Technology StudentStudent number: [email protected] 831 8704

Course supervisor: Neeti Passi

circular versus contour orbits for brain spect imaging

Health & Medicine

brain imaging

contour orbits

normal brain

brain spect acquisition

circular orbit

spect cardiac imaging

d brain phantom data

mri imaging