Martin Satter

Volume image registration by template matching

Abstract A template-matching approach to registration of volumetric images is introduced. The process automatically selects a dozen highly detailed and unique templates (cubic or spherical subvolumes) from one image and locates the templates in another image of the same scene. The centroids of the corresponding templates are used as corresponding control points and the best four correspondences that minimize an error criterion are used to determine the translational and rotational parameters needed to register the images. Use of different similarity measures in template matching and determination of coordinates of corresponding control points with subpixel accuracy are also discussed.

Correlative Whole-Body FDG-PET and Intraoperative Gamma Detection of FDG Distribution in Colorectal Cancer

Purpose: 18F-Fluorodeoxyglucose-positron emission tomography (FDG-PET) is the superior imaging modality for detection of primary and recurrent colorectal cancer compared to magnetic resonance imaging (MRI) or computerized tomography (CT). We investigated the feasibility of developing intraoperative procedures for detection of FDG in tumor deposits in order to assist the surgeon in achieving an optimal reduction of tumor burden.Procedures: Fourteen patients (45-83 years of age) were scanned using FDG-PET followed by Gamma Detection Probe evaluation at laparotomy. One patient did not have a pre-operative FDG-PET scan. The collimated detector probe contained a CdZnTe crystal (7mm diameter x 2mm thick). We used a lower window setting of 200 KeV and an open upper window setting. Fasted patients were given an IV bolus of FDG (4.0-5.7 mCi) 15-20 minutes prior to preparation for surgery. Catheterization and the diuretic Lasix were used to remove FDG activity from the bladder. The time from FDG injection to intraoperative GDP data acquisition varied from 58-110 minutes.Results: In all patients, the GDP detected background activity in normal tissues (aorta, colon, liver, kidney, abdominal wall, mesentery, and urinary bladder). The GDP correctly identified single or multiple tumor foci in 13/14 patients as noted by an audible signal from the control unit (3 S.D. above counts obtained from normal tissues). These tumor foci corresponded to regions of high FDG uptake as seen on FDG-PET scans. The one case that the GDP did not localize was a recurrent mucin pseudomyxoma-producing tumor (acellular, mucinous deposits). Ex vivo GDP evaluations demonstrated significant tumor:normal adjacent tissue activity (audible signals in 6/6 tumor samples tested).Conclusions: These data demonstrate that tumors identified from pre-operative whole-body PET scans can be localized during surgery utilizing a gamma probe detector and FDG.

Quantitative PET with positron emitters that emit prompt gamma rays

The purpose of this work was to determine the feasibility of using positron emitting isotopes that emit prompt gammas to acquire quantitative positron emission tomography (PET) data using standard PET instrumentation. Prompt gammas can contaminate PET data by increasing dead time, converting singles into invalid coincidences, and producing multiple coincidences which can lead to the replacement of valid coincidences by invalid coincidences. The measurements in this work were made by scanning point sources containing F-18, Na-22, and Co-60 and studying the effects of the prompt gammas on the PET data, We found that for the Na-22 point source, the annihilation photon coincidence rate was about 25 times the prompt gamma-annihilation photon coincidence rate in the entire active volume of the scanner. With scatter, the Na-22 prompt gamma-annihilation photon coincidence rate was 1.3 times higher than the F-18 scatter coincidence rate. The most significant effect of the prompt gamma was to increase dead time; the dead time correction factor for Cu-60 was 2.4 times higher than the correction factor for N-13 for the same source activity. We conclude that, in many cases, quantitative PET data can be readily obtained with isotopes that emit prompt gammas, using standard PET 2-D instrumentation. However there are some cases, such as 3-D PET, where prompt gammas could significantly contaminate the PET data.

An adaptive window mechanism for image smoothing

Image smoothing using adaptive windows whose shapes, sizes, and orientations vary with image structure is described. Window size is increased with decreasing gradient magnitude, and window shape and orientation are adjusted in such a way as to smooth most in the direction of least gradient. Rather than performing smoothing isotropically, smoothing is performed in preferred orientations to preserve region boundaries while reducing random noise within regions. Also, instead of performing smoothing uniformly, smoothing is performed more in homogeneous areas than in detailed areas. The proposed adaptive window mechanism is tested in the context of median, mean, and Gaussian filtering, and experimental results are presented using synthetic and real images and compared with a state-of-the-art method.

Functional imaging of a large demyelinating lesion.

PURPOSE To determine the metabolic characterization of a large solitary demyelinating lesion. METHODS Magnetic Resonance Spectroscopy (MRS) and Positron Emission Tomography (PET) studies with 2-deoxy-2-[F-18]fluoro-d-glucose (FDG), carbon-11-methionine (methionine) and carbon-11-choline (choline) were done on the demyelinating lesion. RESULTS The demyelinating lesion exhibited a low glucose uptake, prominent methionine uptake and a minimal choline uptake on the PET studies. MRS data revealed an increased choline to creatine (cho/cr) ratio and a decreased N-acetyl-aspartate to creatine (NAA/cr) ratio, which demonstrated a return to near normal ratios on follow-up study. CONCLUSION The report summarizes the metabolic characteristics of a demyelinating plaque.

A comparative study on the uptake and incorporation of radiolabeled methionine, choline and fluorodeoxyglucose in human astrocytoma.

PURPOSE The goal of this investigation was to evaluate uptake and incorporation of 2-deoxy-2-[18F]fluoro-D-glucose (FDG), 11C-methionine, and 11C-choline in 17 patients suspected of grade-II and grade-III tumors using positron emission tomography (PET) and use in vitro astrocytoma cell lines in order to support in vivo findings. METHODS Seventeen patients with suspected astrocytomas (9 grade-II and 8 grade-III) were studied by PET with FDG and 11C-methionine; and one patient (grade-III) with FDG, 11C-methionine and 11C-choline. Uptake of PET molecular imaging probe was quantitative based on tumor to corresponding contralateral-region uptake ratio, tumor to mean-cortical-uptake ratio, and tumor to white matter uptake ratio. This was correlated with World Health Organization histology grading system and clinical follow-up. Uptake and incorporation of 3H-methionine, 3H-choline and FDG into lipid, RNA, DNA, and protein were investigated in a grade-III human tumor brain-14 astrocytoma cell line. RESULTS A time-dependent increase in the total uptake of 3H-methionine, 3H-choline and FDG was observed in human tumor brain-14 astrocytoma-III cell line. 3H-methionine was incorporated predominantly into proteins (in excess of 40% at 1 h) while 3H-choline incorporated primarily into lipids (in excess of 60% at 1 hr). Total uptake of FDG was accounted for in the free-pool supernatant fraction. In all patients, PET images of 11C-methionine and FDG provided higher tumor to white matter ratios than tumor to corresponding contra-lateral region ratios and tumor to mean cortical uptake ratios. In grade II patients, FDG did not exhibit significant increase in tumor uptake, while 11C-methionine was a good predictor with ratios of approximately 1.50 +/- 0.48. In grade III patients, both FDG and 11C-methionine exhibited higher ratios than for grade II, with 11C-methionine being the greatest (ratios of 2.50 +/- 0.85), possibly suggesting enhanced protein synthesis. With respect to tumor delineating potential, 11C-choline may be equal to or slightly better than 11C-methionine in the subject evaluated with all three probes. CONCLUSIONS Results suggest that a combination of FDG and 11C-methionine is useful in the prediction of histological grade of astrocytomas. In addition, 11C-methionine is better than FDG in delineating tumor boundary for low-grade gliomas. In vitro results suggest that 3H-methionine is significantly incorporated into proteins and provides the major driving force in the uptake of 11C-methionine observed in PET images.

Approximating digital 3D shapes by rational Gaussian surfaces

A method for approximating spherical topology digital shapes by rational Gaussian (RaG) surfaces is presented. Points in a shape are parametrized by approximating the shape with a triangular mesh, determining parameter coordinates at mesh vertices, and finding parameter coordinates at shape points from interpolation of parameter coordinates at mesh vertices. Knowing the locations and parameter coordinates of the shape points, the control points of a RaG surface are determined to approximate the shape with a required accuracy. The process starts from a small set of control points and gradually increases the control points until the error between the surface and the digital shape reduces to a required tolerance. Both triangulation and surface approximation proceed from coarse to fine. Therefore, the method is particularly suitable for multiresolution creation and transmission of digital shapes over the Internet. Application of the proposed method in editing of 3D shapes is demonstrated.

A technique utilizing positron emission tomography and magnetic resonance/computed tomography image fusion to aid in surgical navigation and tumor volume determination.

Brain tumors are histologically heterogeneous. A technique for three-dimensional fusing of computed tomography (CT) or magnetic resonance images (MRI) with positron emission tomography (PET) images is described. This allows the anatomic detail provided by CT or MRI scans to be combined with the information about metabolic activity provided by PET scans. The fused images allowed selection of the most metabolically active portions of tumors. Fusion of CT and MRI images with PET scans has allowed first-pass diagnostic yield by providing the surgeon with a map of anatomical as well as functional (metabolic) detail. We describe a technique to allow routine fusion of MRI, CT, and PET information to help guide the neurosurgeon.

Interactive tools for image segmentation

Interactive tools for segmenting 2-D and 3-D images are presented. These tools allow a user to quickly revise a segmentation result obtained from an automatic method. A thresholding technique is described that finds a unique threshold value for each homogeneous region in an image. The threshold value is found such that variance in the region is minimized under change in the threshold value. Curve- and surface-fitting methods are described that can accurately represent a region boundary in 2-D or 3-D with a parametric curve or a surface, respectively. A curve or a surface is optimized to minimize the number of control points representing a region with a prescribed accuracy. The optimized curve or surface is then revised by moving its control points interactively. Once a curve or a surface is found to accurately enclose a region of interest, it is quantized to produce the final 2-D region contour or 3-D region surface. These interactive tools can be used to revise unsatisfactory results obtained from any automatic segmentation method.

Original Clinical Paper:A Technique Utilizing Positron Emission Tomography and Magnetic Resonance/Computed Tomography Image Fusion to Aid in Surgical Navigation and Tumor Volume Determination

Brain tumors are histologically heterogeneous. A technique for three-dimensional fusing of computed tomography (CT) or magnetic resonance images (MRI) with positron emission tomography (PET) images is described. This allows the anatomic detail provided by CT or MRI scans to be combined with the information about metabolic activity provided by PET scans. The fused images allowed selection of the most metabolically active portions of tumors. Fusion of CT and MRI images with PET scans has allowed first-pass diagnostic yield by providing the surgeon with a map of anatomical as well as functional (metabolic) detail. We describe a technique to allow routine fusion of MRI, CT, and PET information to help guide the neurosurgeon.