Publications

2006
Dimaio SP, Archip N, Hata N, Talos I-F, Warfield SK, Majumdar A, McDannold N, Hynynen K, Morrison PR, Wells WM, et al. Image-guided Neurosurgery at Brigham and Women’s Hospital. IEEE Eng Med Biol Mag. 2006;25 (5) :67-73.
White PJ, Clement GT, Hynynen K. Local Frequency Dependence in Transcranial Ultrasound Transmission. Phys Med Biol. 2006;51 (9) :2293-305.Abstract

The development of large-aperture multiple-source transducer arrays for ultrasound transmission through the human skull has demonstrated the possibility of controlled and substantial acoustic energy delivery into the brain parenchyma without the necessitation of a craniotomy. The individual control of acoustic parameters from each ultrasound source allows for the correction of distortions arising from transmission through the skull bone and also opens up the possibility for electronic steering of the acoustic focus within the brain. In addition, the capability to adjust the frequency of insonation at different locations on the skull can have an effect on ultrasound transmission. To determine the efficacy and applicability of a multiple-frequency approach with such a device, this study examined the frequency dependence of ultrasound transmission in the range of 0.6-1.4 MHz through a series of 17 points on four ex vivo human skulls. Effects beyond those that are characteristic of frequency-dependent attenuation were examined. Using broadband pulses, it was shown that the reflected spectra from the skull revealed information regarding ultrasound transmission at specific frequencies. A multiple-frequency insonation with optimized frequencies over the entirety of five skull specimens was found to yield on average a temporally brief 230% increase in the transmitted intensity with an 88% decrease in time-averaged intensity transmission within the focal volume. This finding demonstrates a potential applicability of a multiple-frequency approach in transcranial ultrasound transmission.

Talos I-F, Mian AZ, Zou KH, Hsu L, Goldberg-Zimring D, Haker S, Bhagwat JG, Mulkern RV. Magnetic Resonance and the Human Brain: Anatomy, Function and Metabolism. Cell Mol Life Sci. 2006;63 (10) :1106-24.Abstract

The introduction and development, over the last three decades, of magnetic resonance (MR) imaging and MR spectroscopy technology for in vivo studies of the human brain represents a truly remarkable achievement, with enormous scientific and clinical ramifications. These effectively non-invasive techniques allow for studies of the anatomy, the function and the metabolism of the living human brain. They have allowed for new understandings of how the healthy brain works and have provided insights into the mechanisms underlying multiple disease processes which affect the brain. Different MR techniques have been developed for studying anatomy, function and metabolism. The primary focus of this review is to describe these different methodologies and to briefly review how they are being employed to more fully appreciate the intricacies associated with the organ, which most distinctly differentiates the human species from the other animal forms on earth.

McDannold N, Hynynen K. Quality Assurance and System Stability of a Clinical MRI-guided Focused Ultrasound System: Four-year Experience. Med Phys. 2006;33 (11) :4307-13.Abstract

To retrospectively evaluate the four-year experience of a quality assurance method for a MRI-guided focused ultrasound system that uses temperature maps acquired during heating in an ultrasound/MRI phantom. This quality assurance method was performed before 148 clinical uterine fibroid thermal ablation treatments. The stability of the peak temperature rise, the targeting accuracy, the shape of the heated zone, and the noise level in the imaging was evaluated. The peak temperature rise was mostly stable for the first three years. An increase in heating was observed when the system was replaced after year three. Detection of this increase was taken into account in the subsequent clinical treatments. A small secondary hotspot was detected by the temperature maps and was seen to be resolved after system calibration. The average standard deviation in unheated regions of the phantom in the temperature maps was 0.5 +/- 0.2 degrees C; it was less than 1 degrees C in all but one procedure. The average initial targeting error was 2.8 +/- 1.8 and 2.8 +/- 2.1 mm in two radial directions and 7.7 +/- 2.9 mm along the ultrasound beam direction. The width of the heating profile was consistent over the four years. This simple method to evaluate the performance appeared to be sensitive to small changes in system performance, which was adequately stable over a four-year time period.

2005
Clatz O, Delingette H, Talos I-F, Golby AJ, Kikinis R, Jolesz FA, Ayache N, Warfield SK. Hybrid Formulation of the Model-based Non-rigid Registration Problem to Improve Accuracy and Robustness. Med Image Comput Comput Assist Interv. 2005;8 (Pt 2) :295-302.Abstract
We present a new algorithm to register 3D pre-operative Magnetic Resonance (MR) images with intra-operative MR images of the brain. This algorithm relies on a robust estimation of the deformation from a sparse set of measured displacements. We propose a new framework to compute iteratively the displacement field starting from an approximation formulation (minimizing the sum of a regularization term and a data error term) and converging toward an interpolation formulation (least square minimization of the data error term). The robustness of the algorithm is achieved through the introduction of an outliers rejection step in this gradual registration process. We ensure the validity of the deformation by the use of a biomechanical model of the brain specific to the patient, discretized with the finite element method. The algorithm has been tested on six cases of brain tumor resection, presenting a brain shift up to 13 mm.
Haker S, Wells WM, Warfield SK, Talos I-F, Bhagwat JG, Goldberg-Zimring D, Mian A, Ohno-Machado L, Zou KH. Combining Classifiers using their Receiver Operating Characteristics and Maximum Likelihood Estimation. Med Image Comput Comput Assist Interv. 2005;8 (Pt 1) :506-14.Abstract

In any medical domain, it is common to have more than one test (classifier) to diagnose a disease. In image analysis, for example, there is often more than one reader or more than one algorithm applied to a certain data set. Combining of classifiers is often helpful, but determining the way in which classifiers should be combined is not trivial. Standard strategies are based on learning classifier combination functions from data. We describe a simple strategy to combine results from classifiers that have not been applied to a common data set, and therefore can not undergo this type of joint training. The strategy, which assumes conditional independence of classifiers, is based on the calculation of a combined Receiver Operating Characteristic (ROC) curve, using maximum likelihood analysis to determine a combination rule for each ROC operating point. We offer some insights into the use of ROC analysis in the field of medical imaging.

Yang Y, Zhu L, Haker S, Tannenbaum AR, Giddens DP. Harmonic Skeleton Guided Evaluation of Stenoses in Human Coronary Arteries. Med Image Comput Comput Assist Interv. 2005;8 (Pt 1) :490-7.Abstract

This paper presents a novel approach that three-dimensionally visualizes and evaluates stenoses in human coronary arteries by using harmonic skeletons. A harmonic skeleton is the center line of a multi-branched tubular surface extracted based on a harmonic function, which is the solution of the Laplace equation. This skeletonization method guarantees smoothness and connectivity and provides a fast and straightforward way to calculate local cross-sectional areas of the arteries, and thus provides the possibility to localize and evaluate coronary artery stenosis, which is a commonly seen pathology in coronary artery disease.

Haker SJ, Mulkern RV, Roebuck JR, Barnes AS, DiMaio S, Hata N, Tempany CM. Magnetic Resonance Guided Prostate Interventions. Top Magn Reson Imaging. 2005;16 (5) :355-68.Abstract

We review our experience using an open 0.5-T magnetic resonance (MR) interventional unit to guide procedures in the prostate. This system allows access to the patient and real-time MR imaging simultaneously and has made it possible to perform prostate biopsy and brachytherapy under MR guidance. We review MR imaging of the prostate and its use in targeted therapy, and describe our use of image processing methods such as image registration to further facilitate precise targeting. We describe current developments with a robot assist system being developed to aid radioactive seed placement.

Zhu L, Haker S, Tannenbaum A. Mass Preserving Registration for Heart MR Images. Med Image Comput Comput Assist Interv. 2005;8 (Pt 2) :147-54.Abstract

This paper presents a new algorithm for non-rigid registration between two doubly-connected regions. Our algorithm is based on harmonic analysis and the theory of optimal mass transport. It assumes an underlining continuum model, in which the total amount of mass is exactly preserved during the transformation of tissues. We use a finite element approach to numerically implement the algorithm.

Nain D, Haker S, Bobick A, Tannenbaum AR. Multiscale 3D Shape Analysis using Spherical Wavelets. Med Image Comput Comput Assist Interv. 2005;8 (Pt 2) :459-67.Abstract

Shape priors attempt to represent biological variations within a population. When variations are global, Principal Component Analysis (PCA) can be used to learn major modes of variation, even from a limited training set. However, when significant local variations exist, PCA typically cannot represent such variations from a small training set. To address this issue, we present a novel algorithm that learns shape variations from data at multiple scales and locations using spherical wavelets and spectral graph partitioning. Our results show that when the training set is small, our algorithm significantly improves the approximation of shapes in a testing set over PCA, which tends to oversmooth data.

Pages