Image-guided port placement for minimally invasive cardiac surgery

Minimally invasive surgery is becoming popular for a number of interventions. Use of robotic surgical systems in coronary artery bypass intervention offers many benefits to patients, but is however limited by remaining challenges in port placement. Choosing the entry ports for the robotic tools has a large impact on the outcome of the surgery, and can be assisted by pre-operative planning and intra-operative guidance techniques. In this thesis, pre-operative 3D computed tomography (CT) imaging is used to plan minimally invasive robotic coronary artery bypass (MIRCAB) surgery. From a patient database, port placement optimization routines are implemented and validated. Computed port placement configurations approximated past expert chosen configurations with an error of 13.7 ±5.1 mm. Following optimization, statistical classification was used to assess patient candidacy for MIRCAB. Various pattern recognition techniques were used to predict MIRCAB success, and could be used in the future to reduce conversion rates to conventional open-chest surgery. Gaussian, Parzen window, and nearest neighbour classifiers all proved able to detect ‘candidate’ and ‘non-candidate’ MIRCAB patients. Intra-operative registration and laser projection of port placements was validated on a phantom and then evaluated in four patient cases. An image-guided laser projection system was developed to map port placement plans from pre-operative 3D images. Port placement mappings on the phantom setup were accurate with an error of 2.4 ± 0.4 mm. In the patient cases, projections remained within 1 cm of computed port positions. Misregistered port placement mappings in human trials were due mainly to the rigid-body registration assumption and can be improved by non-rigid techniques. Overall, this work presents an integrated approach for: 1) pre-operative port placement planning and classification of incoming MIRCAB patients; and 2) intra-operative guidance of port placement. Effective translation of these techniques to the clinic will enable MIRCAB as a more efficacious and accessible procedure

Contrast agent for magnetic resonance imaging of calcifications in breast cancer

Thesis (S.M.)--Harvard-MIT Program in Health Sciences and Technology, 2013.Vita. Cataloged from PDF version of thesis.Includes bibliographical references (pages 37-39).Clinical x-ray mammography cannot delineate between hydroxyapatite and calcium oxalate, the respective forms of calcification in malignant and benign breast tumors. The water-poor nature of solid calcifications makes them difficult to image by conventional MRI. Recently, ultra-short echo time (UTE) MRI has enabled detection of solid calcified structures, but it is not specific to the underlying chemical composition. This thesis presents a hydroxyapatite-targeted gadolinium contrast agent for UTE MRI of calcification in malignant breast cancer. The hydroxyapatite-targeted contrast agent was synthesized by conjugating a bisphosphonate, pamidronate, to a gadolinium chelate. Binding specificity was tested by UTE MRI of the contrast agent reacted with hydroxyapatite, calcium oxalate, and other calcium-based crystals. The sensitivity of the contrast agent for hydroxyapatite was evaluated by UTE MRI: the lowest detectable concentration of hydroxyapatite-adsorbed contrast was 1 pM. Longitudinal relaxation time measurements were used to estimate the apparent relaxivity of the hydroxyapatite contrast agent to be >1000 s-I/mM. The targeted agent relaxivity is enhanced more than a 100-fold compared to conventional untargeted gadolinium contrast agents due to the restricted rotational motion of the contrast agent upon binding to a solid surface. In-vivo MRI of systemic delivery of the contrast agent was demonstrated in an animal model for breast cancer with hydroxyapatite calcifications. Pre- and post-contrast UTE MRI were acquired with systemic contrast agent injections. Dual-echo UTE subtraction images between short and long echoes showed specific uptake of the contrast agent to the calcifications. The mean signal intensity of the calcified regions enhanced by 200% between pre- and post-contrast images, posing the hydroxyapatite-targeted contrast agent as a clinical diagnostic for distinguishing benign and malignant calcification forms in breast cancer.by Jonathan Marmurek.S.M

Functional MRI of working memory and selective attention in vibrotactile frequency discrimination

Abstract Background Focal lesions of the frontal, parietal and temporal lobe may interfere with tactile working memory and attention. To characterise the neural correlates of intact vibrotactile working memory and attention, functional MRI was conducted in 12 healthy young adults. Participants performed a forced-choice vibrotactile frequency discrimination task, comparing a cue stimulus of fixed frequency to their right thumb with a probe stimulus of identical or higher frequency. To investigate working memory, the time interval between the 2 stimuli was pseudo-randomized (either 2 or 8 s). To investigate selective attention, a distractor stimulus was occasionally presented contralaterally, simultaneous to the probe. Results Delayed vibrotactile frequency discrimination, following a probe presented 8 s after the cue in contrast to a probe presented 2 s after the cue, was associated with activation in the bilateral anterior insula and the right inferior parietal cortex. Frequency discrimination under distraction was correlated with activation in the right anterior insula, in the bilateral posterior parietal cortex, and in the right middle temporal gyrus. Conclusion These results support the notion that working memory and attention are organised in partly overlapping neural circuits. In contrast to previous reports in the visual or auditory domain, this study emphasises the involvement of the anterior insula in vibrotactile working memory and selective attention

Functional MRI of working memory and selective attention in vibrotactile frequency discrimination-0

<p><b>Copyright information:</b></p><p>Taken from "Functional MRI of working memory and selective attention in vibrotactile frequency discrimination"</p><p>http://www.biomedcentral.com/1471-2202/8/48</p><p>BMC Neuroscience 2007;8():48-48.</p><p>Published online 4 Jul 2007</p><p>PMCID:PMC1925104.</p><p></p>er rested on a two-button response pad. The arms were extended during the measurement. Pressure points were avoided using foam pads

Functional MRI of working memory and selective attention in vibrotactile frequency discrimination-1

<p><b>Copyright information:</b></p><p>Taken from "Functional MRI of working memory and selective attention in vibrotactile frequency discrimination"</p><p>http://www.biomedcentral.com/1471-2202/8/48</p><p>BMC Neuroscience 2007;8():48-48.</p><p>Published online 4 Jul 2007</p><p>PMCID:PMC1925104.</p><p></p>thumb (cue) followed by an analogous probe of either identical frequency or higher frequency (25 Hz + individual discrimination threshold f). The interstimulus interval (ISI) was either 2 s (as illustrated here) or 8 s. Lower graph: In 25% of trials the probe was paired with a distractor to the left thumb. The stimulation parameters of the distractor were identical to those of the cue. Functional MRI data were obtained continously. Every 2 s, a brain volume consisting of 26 axial was acquired, starting with the beginning of each trial

Functional MRI of working memory and selective attention in vibrotactile frequency discrimination-2

<p><b>Copyright information:</b></p><p>Taken from "Functional MRI of working memory and selective attention in vibrotactile frequency discrimination"</p><p>http://www.biomedcentral.com/1471-2202/8/48</p><p>BMC Neuroscience 2007;8():48-48.</p><p>Published online 4 Jul 2007</p><p>PMCID:PMC1925104.</p><p></p> conditions with and without distractor. Areas with significantly stronger activation following the probe with simultaneous distractor compared to frequency discrimination without distractor are colour-coded in yellow and red, areas with less activation are coded in blue (clustered activation images with an overall corrected p < 0.05). Processing of the probe with distractor was associated with increased activity in the right middle temporal gyrus (1), the right anterior insula (2), the left precuneus (3) and the bilateral posterior parietal cortex (4, 5). Deactivation was seen in the right posterior cingulate gyrus (6), the left medial frontal gyrus (7) and the left precentral gyrus (8). Brain images are shown in radiological convention (the right hemisphere is seen on the left side of the image)