Faculty Bibliography

Volume reconstruction algorithms that provide a three-dimensional (3D) rendering of a tomographic study are now available but not directly applicable to magnetic resonance (MR) studies. The problem with images in such studies is that the gray ranges of tissues overlap. To overcome it, we have developed an interactive graphics editor (IGE) that allows its user to define subregions within the volume of MR images which comprises such a study. The editor performs a statistical analysis of the volume contained in each subregion. With this information the user can enhance individual subregions with such techniques as user-defined remapping of gray levels, the addition of color, the addition of transparency, and spatial filtering. The editor is implemented on a Pixar Image Computer which uses as a host a Sun 3/ISO computer. It has been used by us to create from MR studies three-dimensional images of the brain and knee

A new algorithm for computing cerebral blood flow is shown to overcome compartmental slippage and unstability problems associated with the conventional bicompartmental analysis. The tracer clearance curve is decomposed into a nonnegative linear combination of predetermined flow components. A weighted average of flows above (below) a fixed threshold yields the gray (white) matter flow. The accuracy and the stability of the new algorithm are analyzed by Monte-Carlo simulations, determining the effect of factors such as random error in tracer concentration, gray-white flow difference, tissue content of gray matter, and end-fit time. While the new algorithm requires 50-100% more CPU time and memory space than the bicompartmental method, its accuracy and stability is superior, especially as the conditions of the measurement deteriorate. The results suggest that more than twofold error reduction in measuring the blood flow in pathological brain tissue is possible

Distribution of cerebral blood flow was measured with an array of 200 ultra-pure germanium radiation detectors and 133-Xe by inhalation. The array 'sees' the head as a composite of different subvolumes and enables measurement of the concentration history of tracer every 1-10 sec in each subvolume simultaneously. Subvolume mean flows, (fm), and partition coefficients, lambda m, are derived by compartmental analysis of tissue concentration washout curves. Errors from 'cross talk,' scalp radiation, 'look through,' and assumed partition coefficients are eliminated. Average fm adjusted for 40 mm Hg PACO2 in 14 cortical subvolumes (7 right, 7 left) of four normal 21-24 year old controls ranged from 50 to 60 ml/100 cc tissue/min, and lambda m ranged from 0.97 to 1.14. Average fm and lambda m in white matter was 24 ml/100 cc/min and 1.42 - 1.14 respectively. During CO2 inhalation, right and left hemispheric fm increased 6.4% and 5.7%/mm Hg respectively, whereas white matter fm increased 2.2% and 3.4% mm Hg respectively. There was no systematic difference between front and back or dominant vs non-dominant sides. Three 73-84 year old controls had reduced fm and CO2 reactivity in all subvolumes, lambda m was in the same range as in younger controls. Two patients with intracranial cerebrovascular disease showed excellent localization of ischemic subvolumes. One patient with asymptomatic unilateral 98% stenosis of the internal carotid artery had a similar distribution of blood flow in both hemispheres

Describes a multicounter unit with buffers for storage and transmission of collected counts to the host computer. The system is highly flexible, inexpensive, and able to communicate with computers without direct memory access capability. A prototype has been built at New York University Medical Center for use with a 200-element detector array for measuring the 3-D distribution of cerebral blood flow. The multicounter will free the computer from continuous scanning of the detectors to perform on-line display and storage of collected data. An important feature of the unit is that its proper operation can be quickly verified with the aid of the host computer and detailed diagnosis obtained in case of malfunction

A new stationary 200-element ultrapure germanium (HPGe) array has been tested for accuracy and sensitivity in quantitating the distributed concentration of single-gamma-emitting radionuclides in phantoms approximating the size of the human brain. The phantoms consisted of 42 blocks of 39.1 cm3 average volume. Fourteen different permutations were studied. The concentrations in the blocks varied from 0i to 4.64 muCi/cm3. This first-generation instrument makes it possible to reconstruct the distributed concentration with a mean relative error of 8.3% at 200,000 counts per sample (1,000 counts/detector), and has sensitivities of 6,200 and 12,000 cps, respectively, for 1 muCi/cm3 of Xe-133 and Tc-99. The reconstruction algorithm is based on the conjugate gradient method of solving the set of linear equations that account for geometric, attenuation, and scatter factors. The results have implications for measuring the distribution of the partition coefficients, blood flow, blood volume, and concentration of tracers emitting single gamma photons in 42 anatomic subvolumes (30 cm3 average) of the entire brain simultaneously