Initial Experiences - CAR Lifelong Learning... · Digital tomosynthesis for surgical margin...
Transcript of Initial Experiences - CAR Lifelong Learning... · Digital tomosynthesis for surgical margin...
Digital tomosynthesis for surgical margin assessment in breast-conserving
surgery: Initial Experiences
N. Merchant1, L. Richmond1, M. Skarpathiotakis1, B. Curpen1, R. Jong1, C. Betel1, K. Hack1, A. Maki2 and M. Yaffe1,2
1 Department of Medical Imaging 2 Department of Medical Biophysics Sunnybrook Health Sciences Centre
University of Toronto
Disclosures
This presentation will discuss the investigational use of a medical device (digital breast tomosynthesis).
No other relevant disclosures.
Objectives
Discuss the rationale and potential role for digital tomosynthesis (DT) in the assessment of gross surgical specimen margins following breast conserving surgery
Discuss the technical challenges and artifacts encountered
Discuss potential for future application
Background Achieving negative surgical margins has important clinical
implications in breast-conserving surgery.
This is aided by the radiological assessment of the surgical specimen using ultrasound and/or conventional radiography.
Background
Limitations of conventional imaging modalities
Ultrasound: • As with breast imaging, limited sensitivity for assessment of certain
lesions, particularly microcalcifications
Single specimen radiograph: • Overall sensitivity of 62% and specificity of 95%1
• 2D assessment of an irregularly shaped 3D specimen
• Allows for assessment of inclusion of the lesion, but not all margins are optimally assessed
• Overlapping fibroglandular tissue may obscure the lesion(s)
American Journal of Roentgenology. 1994;162(1): 33-36.
Background Digital Tomosynthesis
• Uses conventional x-rays and a digital detector
• Images acquired while rotating the x-ray tube in an arc around the breast or a volume of tissue
• Images manipulated to produce thin slice tomographic cross-sectional images
Digital detector Specimen with wire
Moving X-ray tube
Digital Tomosynthesis (DT) Over the past decade, Digital Breast Tomosynthesis has been
added to the armamentarium of the Radiologist for breast imaging
Potential to improve breast specimen margin assessment using 3D imaging vs. the conventional 2D radiograph
To further evaluate this….
We carried out a pilot study to assess the feasibility of using DT to improve the accuracy of surgical specimen margin assessment in cases of radiographically visualized breast lesions.
Pilot Specimen DT study Single tertiary care oncology centre
Specialized breast radiologists, surgeons, and pathologists
Inclusion criteria: patients undergoing preoperative wire localization followed by breast-conserving surgery for mammographically visible lesions including calcifications, masses, masses with calcifications, or clips
Exclusion criteria: Mastectomy, mammographically occult lesions, and patients unable to give consent
29 surgical specimens imaged
Specimen DT protocol DT performed immediately following the
specimen radiograph using the same equipment
Approximate scan time: 7 seconds
9 projection images acquired over a 25-degree angular range in a step-and-shoot manner
Iterative reconstruction algorithm used to produce a reconstructed volume with slices every 0.5 mm in the z-direction
Study methodology Image reviewer: Radiologist with subspecialty training in
breast imaging
Anonymized specimen radiographs and DT images reviewed by same reader at separate sittings
Access to all pre-operative imaging for both sets of imaging reviews, but blinded to the other modality images and the pathology report
Superior, inferior, lateral and medial margins measured for both imaging modalities
Pathologic margins used as ground truth
Technical Challenges Multiple technical challenges and artifacts were encountered
upon review of the DT images
Led to concerns about variability and reproducibility of the data
Data felt to be unusable
The remainder of this presentation discusses the challenges we encountered…
Motion Artifact To maintain anatomical distances/depths,
specimens were not compressed during image acquisition
Specimen prone to minor motion as the machine moved through the range of angles
• blurring of lesion margins and fine calcifications
• blurring of the in-plane specimen margin
Specimen secured with plastic wrap which was then taped to the imaging surface variable amount of motion artifact Hover mouse over image
to Play
Wire Echo Artifact Extensive echo artifact relating to
the localization wire
Arc/fan shaped distribution in a single plane, over multiple slices
Related to image acquisition over multiple angles +/- motion artifact
Limited assessment by obscuring adjacent small lesions / calcifications in that plane
Hover mouse over image to Play
Specimen Radiograph vs. DT
Specimen Radiograph No motion artifact
DT image Wire echo artifact and image blur
2a
2b Specimen Radiograph
No motion artifact DT image (in plane of wire) No significant motion artifact
Wire Echo Artifact
Potential solutions to minimize this artifact:
• Manipulating the reconstruction algorithm may help suppress/minimize this artifact o However, this may also affect the appearance of the lesions within the
specimen
• Replacing localization wires with radioactive seeds
Delineating margins DT measures x-ray transmission through
tissue over a range of angles series of images reconstructed for different heights above detector (z-axis)
The true margin in a particular imaging plane should produce a sharper margin • However, in many cases it was difficult to
delineate the true margin in that specific plane from the margin of an adjacent plane
Each image includes tissue at the height of focal plane and overlapping tissue • This factor + multilobulated margins of
specimens + motion artifact appearance of multiple possible margins
Well-visualized cancer with minimal motion or wire echo artifact.
Can you define the margins of the specimen on each plane?
Hover mouse over image to Play
Posterior Margin Visualization
Posterior-most aspect of specimen (directly on the specimen plate) incompletely included on the reconstructed images • improved by raising the specimen on a clear plastic block
Directly on imaging plate Raised on block
Note extensive motion artifact and wire echo artifact on both sets of images
Hover mouse over images to play clips
(Cine: Posterior Anterior)
Additional Considerations
Artifact inherent to the tomosynthesis equipment: • Degree of background noise inherent to the
tomosynthesis unit may vary between vendors
• All specimens were imaged using the same machine
• Images acquired using step-and-shoot method
• Trial using other units/vendors may be considered
Conclusion While the concept of multiplanar specimen margin analysis
with DT has potential, the multiple challenges and artifacts encountered in this preliminary study limit its practical application, at least in its current state.
Future work on minimizing the technical issues may help improve the quality of the images, potentially making it more feasible and applicable to general practice. • Ideas to explore…
o Adding reconstruction algorithms to suppress artifacts such as the wire echo artifact
o Using radioactive seeds for localization instead of wires
o Trial of continuous tube motion during x-ray exposure vs. the step- and- shoot method used in this study