Observer Study of Reconstruction Strategies for Detection of Solitary Pulmonary Nodules Using Hybrid

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Observer Study of Reconstruction Strategies for
Detection of Solitary Pulmonary Nodules Using
Hybrid NeoTect SPECT Images

• Xiaoming Zheng, PhD.
• 20 October, 2004

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Outlines

• Lung Cancer and SPECT/PET
• NeoTect in Lung SPECT
• Image Reconstructions RBI vs FBP
• Hybrid Images Clinical Reality
• Observer Studies Human vs Numerical
• ROC Receiver Operating Characteristics
• Results and Conclusions

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Leading Causes of Cancer Deaths
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NSCLC Non-Small-Cell-Lung-Cancer

• Surgery is providing the best chance of cure if
  tumor can be re-sected completely.
• If cancer has spread to contra-lateral lymph
  nodes or beyond the chest surgery alone is not
  useful. Chemotherapy and/or radiotherapy are
  usually applied. These measures are rarely
  curative

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SPN Solitary Pulmonary Nodule

• Approx. 30 of new cases of lung cancer are found
  as an SPN
• An SPN is defined as
• single pulmonary lesion
• well defined borders
• mean diameter not more than 3 cm
• Found in 1 500 chest X-rays

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SPECT and PET
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NeoTect/SPECT vs FDG/PET
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NeoTect (99mTc-Depreotide)

• Binds to Somatostatin receptors, which are
  over-expressed in lung cancer (NSCLC and SCLC)
• Has a negative predictive value of up to 98 in
  combination with CT or chest X-ray for SPN
• Procedure is non-invasive
• 99mTc-labelled - readily available
• Procedure is easy
• Can be used wherever SPECT is available

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NeoTect
- a small synthetic peptide - 10 amino acids,
mol. wt. 1358 Da - binding region for the
somatostatin receptor - radio-labeled with 99mTc
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How NeoTect Works

• Malignant tumors over-express somatostatin
  receptors (SSTRs)
• NeoTect binds to and detects SSTRs
• Most benign lesions do not over-express SSTRs

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Normal Transaxial SPECT Images
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Coronal SPECT
72 yr female smoker, complaining of weight loss
chest x-ray 2.5 cm LUL lesion CT LUL 2.0 cm
spiculated mass Histopathology (CT guided FNA
biopsy) poorly-differentiated adenocarcinoma
Transaxial SPECT
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Aims of This Work

• Use hybrid images of lung tumor imaging agent
  Tc-99m NeoTect in Localization Receiver Operating
  Characteristic (LROC) studies to determine
  reconstruction parameters and whether iterative
  reconstruction with attenuation, scatter, and
  distant resolution compensation should replace
  FBP clinically.

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Why Hybrid Images

• The Optimization of reconstruction parameters,
  and determination of whether iterative
  reconstruction should replace FBP clinically
  should be based on tasks which closely
  approximate the clinical application of the
  images
• The use of hybrid images or studies represents a
  practical alternative to the use of purely
  clinical acquisitions for observer studies.

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How Hybrid Images Were Created

• Simulated lesions are added to know normal
  clinical acquisitions
• Monte Carlo simulation package SIMIND was used to
  simulate lesions.
• Nine normal patients projection data were used
  to create 162 tumors randomly distributed within
  the lung regions.
• Tumors were 1 cm in diameter which is the
  smallest tumor could be detected by CT.

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NeoTect ProjectionsFrom Clinical 9 Patients
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Tumor Source ProjectionsFrom Monte Carlo
Simulation
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Images Reconstructions

• Iterative Reconstruction Rescaled Block
  Iterative Algorithm including attenuation,
  scatter, and distance resolution compensation.
  Parameters tested iteration 1,3,5,7,10 and post
  Gaussian filter FWHM 0,1,2,3,4 pixels
• Filtered Back-Projection Parameters tested
  Butterworth filter cut-off frequencies 0.10,
  0.15, 0.20, 0.25 and 0.30 pixel-1

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Filtered Back-Projection
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Butterworth Filter and Cutoff Frequency
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FBP Reconstructed Images
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Iterative Reconstruction
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Rescaled Block Iterative Reconstruction Algorithm
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Attenuation Compensation
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Scatter Compensation
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Resolution Compensation
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RBI Reconstructed Images
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Receiver Operating Characteristics
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Images for Observers
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Numerical Observers
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Types of Channels
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Human Observer Interface RBI
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Human Observer Interface FBP
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Numerical Observer Results RBI
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Numerical Observer Results FBP
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Human Observer Results
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Conclusions

• Iterative RBI-EM including all corrections
  performs better than that of FBP.
• The best performance reconstruction strategy is
  RBI-EM with 5 iteration and 1 pixel FWHM in
  Gaussian post-filtering.
• Numerical observer with and without mean
  background subtraction set the upper and lower
  bounds achievable by human observer.

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Acknowlegements

• This work was supported by a Charles Sturt
  University Special Study grant and a NIH research
  grant.
• The co-authors of this work are Prof Mike King,
  Dr Howard Gifford and Dr Hennie Pretorius at the
  University of Massachusetts Medical School.