title: Comparison of breast specific gamma imaging and molecular breast tomosynthesis in breast cancer detection: Evaluation in phantoms.
abstract: OBJECTIVE
  Breast specific gamma imaging or molecular breast imaging (BSGI) obtains 2D images of (99m)Tc sestamibi distribution in the breast. Molecular breast tomosynthesis (MBT) maps the tracer distribution in 3D by acquiring multiple projections over a limited angular range. Here, the authors compare the performance of the two technologies in terms of spatial resolution, lesion contrast, and contrast-to-noise ratio (CNR) in phantom studies under conditions of clinically relevant sestamibi dose and imaging time.
  
  
  METHODS
  The systems tested were a Dilon 6800 and a MBT prototype developed at the University of Virginia. Both systems comprise a pixelated sodium iodide scintillator, an array of position sensitive photomultipliers, and a parallel hole collimator. The active areas and energy resolution of the systems are similar. System sensitivity, spatial resolution, lesion contrast, and CNR were measured using a Petri dish, a point source phantom, and a breast phantom containing simulated lesions at two depths, respectively. A single BSGI projection was acquired. Five MBT projections were acquired over ±20°. For both modalities, the total scan count density was comparable to that observed for each in typical 10 min human scans following injection of 22 mCi (814 MBq) of (99m)Tc-sestamibi. To assess the impact of reducing the tracer dose, the pixel counts of projection images were later binomially subsampled by a factor of 2 to give images corresponding to an injected activity of approximately 11 mCi (407 MBq). Both unprocessed (pixelated) BSGI projections and interpolated (smoothed) BSGI images displayed by default on the Dilon 6800 workstation were analyzed. Volumetric images were reconstructed from the MBT projections using a maximum likelihood expectation maximization algorithm and extracted slices were analyzed.
  
  
  RESULTS
  Over a depth range of 1.5-7.5 cm, BSGI spatial resolution was 5.6-11.5 mm in unprocessed projections and 5.7-12.0 mm in interpolated images. Over the same range, the in-slice MBT spatial resolution was 6.7-9.4 mm. Lesion contrast was significantly improved with MBT relative to BSGI for five out of eight lesions imaged at either the 22 mCi or the 11 mCi dose level (p < 0.05). At both dose levels, significant improvements in CNR with MBT were also found for five out of eight lesions (9.8, 7.8, 6.2 mm lesions at water depth of 1.7 cm and 9.8, 7.8 mm lesions at water depth of 4.5 cm, p < 0.05). The 6.2 and 4.9 mm lesions located at 4.5 cm below the water surface were not visible in either modality at either activity level.
  
  
  CONCLUSIONS
  Under conditions of equal dose, imaging time and similar detectors, compared to BSGI, MBT provided higher lesion contrast, higher CNR, and spatial resolution that was less depth dependent.
authors.affiliation: Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, Virginia 22908.
authors.forename: Zongyi
authors.initials: Z
authors.lastname: Gong
authors.affiliation: Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, Virginia 22908; Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia 22908; and Department of Physics, University of Virginia, Charlottesville, Virginia 22904.
authors.forename: Mark B
authors.initials: MB
authors.lastname: Williams
mesh_terms: D001940:Breast / Q000000981:diagnostic imaging* / Q000378:metabolism*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D002138:Calibration; D004867:Equipment Design; D005260:Female; D015902:Gamma Cameras; D005720:Gamma Rays; D006801:Humans; D008954:Models, Biological; D057054:Molecular Imaging / Q000295:instrumentation / Q000379:methods; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011877:Radionuclide Imaging / Q000295:instrumentation / Q000379:methods; D019275:Radiopharmaceuticals; D017256:Technetium Tc 99m Sestamibi
chemical_list: D019275:Radiopharmaceuticals; D017256:Technetium Tc 99m Sestamibi