title: Towards clinical prostate ultrasound elastography using full inversion approach.
abstract: OBJECTIVE
  Various types of cancers including prostate cancer are known to be associated with biological changes that lead to tissue stiffening. Digital rectal examination is based on manually palpating the prostate tissue via the rectum. This test lacks sufficient accuracy required for early diagnosis which is necessary for effective management of prostate cancer. To develop an effective prostate cancer diagnostic technique, the authors propose an imaging technique that maps the distribution of the relative prostate tissue's elasticity modulus. Unlike digital rectal examination, this technique is quantitative, capable of accurately detecting small prostate lesions that cannot be sensed by manual palpation, and its accuracy is independent of the physician's experience.
  
  
  METHODS
  The proposed technique is a quasistatic elastography technique which uses ultrasound imaging to acquire tissue displacements resulting from transrectal ultrasound mechanical stimulation. The system involves a standard ultrasound imaging unit with accessibility to its radiofrequency data. The displacements are used as data for the tissue elasticity reconstruction. This reconstruction does not require tissue segmentation and is based on physics governing tissue mechanics. It is formulated using an inverse problem framework where elastic tissue deformation equations are fully inverted using an iterative scheme where each iteration involves stress calculation followed by elastic modulus updating until convergence is achieved.In silico and tissue mimicking phantom studies were conducted to validate the proposed technique, followed by a clinical pilot study involving two prostate cancer patients with whole-mount histopathology analysis on prostatectomy specimens to confirm a cancer location.
  
  
  RESULTS
  The phantom studies demonstrated robustness and reasonably high accuracy of the proposed method. Obtained Young's modulus ratios indicated reconstruction errors of less than 12%. Reconstructed elastic modulus images of the two clinical cases were compared to whole-mount histopathology slides where cancerous areas were identified. This comparison indicated marked tissue stiffening in the cancer area with reasonably accurate consistency observed between cancerous lesions identified by histopathology and high stiffness areas of the elastography images.
  
  
  CONCLUSIONS
  Results obtained from the phantom and patient studies indicate that the proposed method is reasonably accurate for detecting cancerous lesions. The proposed system does not require any additional hardware attachment for mechanical stimulation or data acquisition while the elasticity reconstruction algorithm can be easily implemented, leading to a low cost system that can be potentially utilized as an effective clinical tool for prostate cancer diagnosis.
authors.affiliation: Department of Electrical and Computer Engineering, Western University, London, Ontario N6A 5B9, Canada.
authors.forename: Seyed Reza
authors.initials: SR
authors.lastname: Mousavi
authors.affiliation: Departments of Medical Biophysics, Radiation Oncology and Imaging Research - Physical Sciences, University of Toronto and Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5, Canada.
authors.forename: Ali
authors.initials: A
authors.lastname: Sadeghi-Naini
authors.affiliation: Departments of Medical Biophysics, Radiation Oncology and Imaging Research - Physical Sciences, University of Toronto and Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5, Canada.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Czarnota
authors.affiliation: Department of Electrical and Computer Engineering, Western University, London, Ontario N6A 5B9, Canada; Department of Medical Biophysics, Western University, London, Ontario N6A 5C1, Canada; Graduate Program in Biomedical Engineering, Western University, London, Ontario N6A 5B9, Canada; and Imaging Research Laboratories, Robarts Research Institute (RRI), London, Ontario N6A 5K8, Canada.
authors.forename: Abbas
authors.initials: A
authors.lastname: Samani
mesh_terms: D000465:Algorithms; D004548:Elasticity; D054459:Elasticity Imaging Techniques / Q000379:methods*; D006801:Humans; D008297:Male; D019047:Phantoms, Imaging; D011467:Prostate / Q000000981:diagnostic imaging* / Q000473:pathology; D011470:Prostatic Hyperplasia / Q000175:diagnosis / Q000473:pathology; D012007:Rectum / Q000000981:diagnostic imaging / Q000473:pathology; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D014463:Ultrasonography / Q000379:methods*