Thilaka S. Sumanaweera

Noninvasive stereotactic radiosurgery (CyberHeart) for creation of ablation lesions in the atrium

BACKGROUND A variety of catheter-based energy modalities are used for cardiac ablation to treat arrhythmias. Robotic radiosurgery is increasingly being utilized to successfully accomplish precise tissue ablation in anatomically remote areas. OBJECTIVE The purpose of this study was to examine the experimental feasibility of a noninvasive method using stereotactic robotic radiosurgery (SRS) to create cardiac lesions. METHODS Sixteen (16) Hanford-Sinclair mini swine (weight 40-70 kg) under general anesthesia were studied. Baseline computed tomographic scans were performed, followed by electroanatomic mapping using the CARTO system. Stereotactic robotic radiosurgery was performed using the CyberHeart system, with predetermined targets at the cavotricuspid isthmus, AV node, pulmonary vein-left atrial junction, or left atrial appendage. From 25 to 196 days after treatment, the animals were investigated with repeat electroanatomic voltage mapping and transesophageal echocardiography, when possible. The animals then were sacrificed and pathology specimens taken. RESULTS Dose ranging suggested that 25 Gy was needed to produce an electrophysiologic effect. The time course showed an electrophysiologic effect consistently by 90 days. The method was feasible for producing bidirectional cavotricuspid isthmus block and AV nodal conduction block. The pulmonary vein-left atrial junction and left atrial appendage showed marked voltage reduction to less than 0.05 mV. No spontaneous arrhythmias were observed. Pathology specimens showed no evidence of radiation damage outside the target. Histology samples from target sites showed effects consistent with X-beam radiation. CONCLUSION Stereotactic robotic radiosurgery can produce cavotricuspid isthmus block, AV nodal block, and significant decreased voltage at the pulmonary vein-left atrial junction. No other organ damage was seen. The study findings demonstrate the feasibility of this noninvasive treatment method for creating cardiac lesions. This approach merits further investigation in the treatment of arrhythmias.

In vivo dose measurement using TLDs and MOSFET dosimeters for cardiac radiosurgery

In vivo measurements were made of the dose delivered to animal models in an effort to develop a method for treating cardiac arrhythmia using radiation. This treatment would replace RF energy (currently used to create cardiac scar) with ionizing radiation. In the current study, the pulmonary vein ostia of animal models were irradiated with 6 MV X‐rays in order to produce a scar that would block aberrant signals characteristic of atrial fibrillation. The CyberKnife radiosurgery system was used to deliver planned treatments of 20–35 Gy in a single fraction to four animals. The Synchrony system was used to track respiratory motion of the heart, while the contractile motion of the heart was untracked. The dose was measured on the epicardial surface near the right pulmonary vein and on the esophagus using surgically implanted TLD dosimeters, or in the coronary sinus using a MOSFET dosimeter placed using a catheter. The doses measured on the epicardium with TLDs averaged 5% less than predicted for those locations, while doses measured in the coronary sinus with the MOSFET sensor nearest the target averaged 6% less than the predicted dose. The measurements on the esophagus averaged 25% less than predicted. These results provide an indication of the accuracy with which the treatment planning methods accounted for the motion of the target, with its respiratory and cardiac components. This is the first report on the accuracy of CyberKnife dose delivery to cardiac targets. PACS numbers: 87.53.Ly, 87.53.Bn

Removing local motion from ultrasonic images using nonaffine registration for contrast quantification

A contrast quantification package has been developed to be part of a medical ultrasound system. This package provides motion compensation through nonaffine image registration. An explanation of the image registration system is given. A set of analyses made with this system is presented; they show that the registration system provides significant improvements over using images without motion correction.

Cardiac image fusion

We present a method to enhance the image quality and the field of view of echocardiography by combining the data acquired through multiple windows to the heart using a commercial 1D transducer. The advantages are wider field of views and better border delineation. No external position sensing devices or specialized, and thus expensive, transducers are required.