@article {10.1371/journal.pone.0027372,
	title = {An Open Environment CT-US Fusion for Tissue Segmentation during Interventional Guidance},
	journal = {PLoS ONE},
	volume = {6},
	number = {11},
	year = {2011},
	month = {11},
	pages = {e27372},
	publisher = {Public Library of Science},
	abstract = {<p>Therapeutic ultrasound (US) can be noninvasively focused to activate drugs, ablate tumors and deliver drugs beyond the blood brain barrier. However, well-controlled guidance of US therapy requires fusion with a navigational modality, such as magnetic resonance imaging (MRI) or X-ray computed tomography (CT). Here, we developed and validated tissue characterization using a fusion between US and CT. The performance of the CT/US fusion was quantified by the calibration error, target registration error and fiducial registration error. Met-1 tumors in the fat pads of 12 female FVB mice provided a model of developing breast cancer with which to evaluate CT-based tissue segmentation. Hounsfield units (HU) within the tumor and surrounding fat pad were quantified, validated with histology and segmented for parametric analysis (fat: -300 to 0 HU, protein-rich: 1 to 300 HU, and bone: HU\&gt;300). Our open source CT/US fusion system differentiated soft tissue, bone and fat with a spatial accuracy of \~{}1 mm. Region of interest (ROI) analysis of the tumor and surrounding fat pad using a 1 mm<sup>2</sup> ROI resulted in mean HU of 68{\textpm}44 within the tumor and -97{\textpm}52 within the fat pad adjacent to the tumor (p\&lt;0.005). The tumor area measured by CT and histology was correlated (r<sup>2</sup> = 0.92), while the area designated as fat decreased with increasing tumor size (r<sup>2</sup> = 0.51). Analysis of CT and histology images of the tumor and surrounding fat pad revealed an average percentage of fat of 65.3\% vs. 75.2\%, 36.5\% vs. 48.4\%, and 31.6\% vs. 38.5\% for tumors \&lt;75 mm<sup>3</sup>, 75{\textendash}150 mm<sup>3</sup> and \&gt;150 mm<sup>3</sup>, respectively. Further, CT mapped bone-soft tissue interfaces near the acoustic beam during real-time imaging. Combined CT/US is a feasible method for guiding interventions by tracking the acoustic focus within a pre-acquired CT image volume and characterizing tissues proximal to and surrounding the acoustic focus.</p>},
	doi = {10.1371/journal.pone.0027372},
	url = {http://dx.doi.org/10.1371\%2Fjournal.pone.0027372},
	author = {Caskey, , Charles F. and Hlawitschka, , Mario and Qin, , Shengping and Mahakian, , Lisa M. and Cardiff, , Robert D. and Boone, , John M. and Ferrara, , Katherine W.}
}
