Kenneth F. Koral

Demonstration of accuracy and clinical versatility of mutual information for automatic multimodality image fusion using affine and thin-plate spline warped geometric deformations

This paper applies and evaluates an automatic mutual information-based registration algorithm across a broad spectrum of multimodal volume data sets. The algorithm requires little or no pre-processing, minimal user input and easily implements either affine, i.e. linear or thin-plate spline (TPS) warped registrations. We have evaluated the algorithm in phantom studies as well as in selected cases where few other algorithms could perform as well, if at all, to demonstrate the value of this new method. Pairs of multimodal gray-scale volume data sets were registered by iteratively changing registration parameters to maximize mutual information. Quantitative registration errors were assessed in registrations of a thorax phantom using PET/CT and in the National Library of Medicines Visible Male using MRI T2-/T1-weighted acquisitions. Registrations of diverse clinical data sets were demonstrated including rotate-translate mapping of PET/MRI brain scans with significant missing data, full affine mapping of thoracic PET/CT and rotate-translate mapping of abdominal SPECT/CT. A five-point thin-plate spline (TPS) warped registration of thoracic PET/CT is also demonstrated. The registration algorithm converged in times ranging between 3.5 and 31 min for affine clinical registrations and 57 min for TPS warping. Mean error vector lengths for rotate-translate registrations were measured to be subvoxel in phantoms. More importantly the rotate-translate algorithm performs well even with missing data. The demonstrated clinical fusions are qualitatively excellent at all levels. We conclude that such automatic, rapid, robust algorithms significantly increase the likelihood that multimodality registrations will be routinely used to aid clinical diagnoses and post-therapeutic assessment in the near future.

Scatter modelling and compensation in emission tomography

In nuclear medicine, clinical assessment and diagnosis are generally based on qualitative assessment of the distribution pattern of radiotracers used. In addition, emission tomography (SPECT and PET) imaging methods offer the possibility of quantitative assessment of tracer concentration in vivo to quantify relevant parameters in clinical and research settings, provided accurate correction for the physical degrading factors (e.g. attenuation, scatter, partial volume effects) hampering their quantitative accuracy are applied. This review addresses the problem of Compton scattering as the dominant photon interaction phenomenon in emission tomography and discusses its impact on both the quality of reconstructed clinical images and the accuracy of quantitative analysis. After a general introduction, there is a section in which scatter modelling in uniform and non-uniform media is described in detail. This is followed by an overview of scatter compensation techniques and evaluation strategies used for the assessment of these correction methods. In the process, emphasis is placed on the clinical impact of image degradation due to Compton scattering. This, in turn, stresses the need for implementation of more accurate algorithms in software supplied by scanner manufacturers, although the choice of a general-purpose algorithm or algorithms may be difficult.

A method for a fully automatic definition of coronary arterial edges from cineangiograms

The authors describe a novel algorithm, known as sequential edge linking (SEL), for the automatic definition of coronary arterial edges in cineangiograms. This algorithm is based on sequential tree searching of possible coronary artery boundary locations. Using a coronary artery phantom, the authors compared the results obtained using SEL with hand-traced boundaries. Using a magnification of 2x, the results are generally good, with the average error being 1.7% of the diameter. Actual coronary artery images were also processed and a similar comparison indicated that total areas were comparable but the hand-drawn stenoses were, on average, 7% greater than the unobstructed diameter. Based on these data it is concluded that the SEL algorithm is an accurate method for fully automatic definition of coronary artery dimensions.

SPRINT II: a second generation single photon ring tomograph

SPRINT II is a stationary detector ring tomograph designed for brain imaging. Eleven two-dimensional sodium iodide camera modules that use maximum-likelihood position logic are arranged in a 50-cm-diameter ring with a scintillator packing fraction of 96%. A 34-cm-diameter rotating lead aperture ring containing either 10 or 12 slits is used for in-plane collimation, while the z-axis collimator is constructed of parallel lead foil rings. The field of view is 22 cm in diameter by 12 cm long. Sensitivity is 10 count/s/muCi for an on-axis (99m)Tc point source and 8500 count/s/muCi/cm(3) for 19.8-cm-diameter by 6.2-cm-long cylindrical source. Longitudinal resolution is 10 mm FWHM, and in-plane resolution varies from 8 mm FWHM on-axis to 5 mm FWHM at a radius of 9 cm. Performance results are presented.

131I-Tositumomab Radioimmunotherapy: Initial Tumor Dose–Response Results Using 3-Dimensional Dosimetry Including Radiobiologic Modeling

For optimal treatment planning in radionuclide therapy, robust tumor dose–response correlations must be established. Here, fully 3-dimensional (3D) dosimetry was performed coupling SPECT/CT at multiple time points with Monte Carlo–based voxel-by-voxel dosimetry to examine such correlations. Methods: Twenty patients undergoing 131I-tositumomab for the treatment of refractory B-cell lymphoma volunteered for the study. Sixty tumors were imaged. Activity quantification and dosimetry were performed using previously developed 3D algorithms for SPECT reconstruction and absorbed dose estimation. Tumors were outlined on CT at multiple time points to obtain absorbed dose distributions in the presence of tumor deformation and regression. Equivalent uniform dose (EUD) was calculated to assess the biologic effects of the nonuniform absorbed dose, including the cold antibody effect. Response for correlation analysis was determined on the basis of the percentage reduction in the product of the largest perpendicular tumor diameters on CT at 2 mo. Overall response classification (as complete response, partial response, stable disease, or progressive disease) used for prediction analysis was based on criteria that included findings on PET. Results: Of the evaluated tumor-absorbed dose summary measures (mean absorbed dose, EUD, and other measures from dose-volume histogram analysis), a statistically significant correlation with response was seen only with EUD (r = 0.36 and P = 0.006 at the individual tumor level; r = 0.46 and P = 0.048 at the patient level). The median value of mean absorbed dose for stable disease, partial response, and complete response patients was 196, 346, and 342 cGy, respectively, whereas the median value of EUD for each of these categories was 170, 363, and 406 cGy, respectively. At a threshold of 200 cGy, both mean absorbed dose and EUD had a positive predictive value for responders (partial response + complete response) of 0.875 (14/16) and a negative predictive value of 1.0 (3/3). Conclusion: Improved dose–response correlations were demonstrated when EUD incorporating the cold antibody effect was used instead of the conventionally used mean tumor-absorbed dose. This work demonstrates the importance of 3D calculation and radiobiologic modeling when estimating absorbed dose for correlation with outcome.

A Hybrid Maximum Likelihood Position Computer for Scintillation Cameras

Maximum likelihood (ML) estimators offer advantages of improved spatial resolution and linearity over traditional position estimates in position sensitive detectors. We have constructed a two board, multibus based hybrid position computer capable of performing the ML estimate at SPECT countrates. In addition, the board can implement any estimate linear in the photomultiplier tube outputs.

An overview of imaging techniques and physical aspects of treatment planning in radioimmunotherapy

Planar and tomographic imaging techniques and methods of treatment planning in clinical radioimmunotherapy are reviewed. In clinical trials, the data needed for dosimetry and treatment planning are, in most cases, obtained from noninvasive imaging procedures. The required data include tumor and normal organ volumes, the activity of radiolabeled antibodies taken up in these volumes, and the pharmacokinetics of the administered activity of radiolabeled antibodies. Therefore, the topics addressed in this review include: (1) Volume determination of tumors and normal organs from x-ray-computed tomography and magnetic resonance imaging, (2) quantitation of the activity of radiolabeled antibodies in tumors and normal organs from planar gamma camera views, (3) quantitative single-photon emission computed tomography and positron emission tomography, (4) correlative image analysis, and (5) treatment planning in clinical radioimmunotherapy.

SPRINT: A Stationary Detector Single Photon Ring Tomograph for Brain Imaging

During the last two decades, various Doppler methods have been successfully used to screen patients with significant cerebral and peripheral vascular disease. In general terms, the principal advantages of Doppler ultrasound techniques in the evaluation of atherosclerotic lesions are that they: 1) are noninvasive, 2) are nontraumatic, 3) are relatively inexpensive, 4) provide anatomical and physiological data, and 5) provide direct and dynamic measurements. Nevertheless, the general limitations of the techniques are of equal importance: 1) the techniques are difficult in some subjects due to obesity and anatomical variations; 2) the technique cannot examine tissues surrounded by air or bone; 3) the techniques require operator skill and a thorough knowledge of human anatomy and cardiovascular dynamics; 4) the techniques have finite spatial resolutions which may compromise the important measurement of vessel diameter, ulceration, and percent stenosis; and 5) the techniques have finite velocity measuring capabilities which may compromise some measurements of highly disturbed blood velocities outside the range of 2-200 cm/sec. As clinical demands for the early diagnosis and quantification of vascular lesions increased, improvements in Doppler ultrasonics and spectra analysis significantly increased the technical and clinical capabilities of existing simple, inexpensive instruments. Presently, both anatomical and physiological images along with quantitative Doppler spectra from superficial and deep-lying vessels can be obtained. Consequently, the ability of Vascular Laboratory, Clinical Research Division; Lovelace Medical Foundation, and the University of New Mexico School of Medicine, Albuquerque, New Mexico 87108 Manuscript received at IEEE April 30, 1982. new expensive imaging equipment to quantitate atherosclerotic lesions using spectral analysis techniques compares favorably with the interpretational precision of standard invasive or intravenous digital angiography. New data suggest that unique hemodynamic information which reflects the effects of cardiac output and vascular input impedance on the hemodynamic consequences of an anatomical lesion can also be obtained. This paper will 1) briefly discuss the general considerations of Doppler ultrasonics; 2) critique the specific characteristics and utility of standard clinical Doppler units; and 3) discuss the ability of new, multipurpose equipment to quantitate (both anatomically and physiologically) atherosclerotic lesions throughout the cardiovascular system.

Volume reduction versus radiation dose for tumors in previously untreated lymphoma patients who received iodine-131 tositumomab therapy. Conjugate views compared with a hybrid method.

A Phase II study of previously untreated patients with malignant low grade follicular lymphoma given a combination of unlabeled tositumomab and tositumomab labeled with iodine‐131 has recently been completed. The responses of these patients have been characterized, and for some of them tumor dosimetry during therapy has been estimated not only by pretherapy tracer conjugate views but also by a hybrid method.

A parallel Monte Carlo code for planar and SPECT imaging: implementation, verification and applications in 131I SPECT

This paper reports the implementation of the SIMIND Monte Carlo code on an IBM SP2 distributed memory parallel computer. Basic aspects of running Monte Carlo particle transport calculations on parallel architectures are described. Our parallelization is based on equally partitioning photons among the processors and uses the Message Passing Interface (MPI) library for interprocessor communication and the Scalable Parallel Random Number Generator (SPRNG) to generate uncorrelated random number streams. These parallelization techniques are also applicable to other distributed memory architectures. A linear increase in computing speed with the number of processors is demonstrated for up to 32 processors. This speed-up is especially significant in Single Photon Emission Computed Tomography (SPECT) simulations involving higher energy photon emitters, where explicit modeling of the phantom and collimator is required. For (131)I, the accuracy of the parallel code is demonstrated by comparing simulated and experimental SPECT images from a heart/thorax phantom. Clinically realistic SPECT simulations using the voxel-man phantom are carried out to assess scatter and attenuation correction.