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Objective: To characterize the ability of an automatic lung nodule segmentation algorithm to measure small nodule dimensions and growth rates. Methods: A phantom of 20 sets of 6 balls each (11 different nylon balls and 9 acrylic balls) of 1 to 9.5 mm in diameter, in foam, was imaged using x-ray computed tomography with slice thicknesses of 5, 2.5, and 1.25 mm, pitches of 3 and 6, and standard and lung resolution. Measurements consisted of volume and maximum in-plane cross-sectional areas and their derived maximum and effective diameters. Growth rates were simulated using pairs of groups of balls. Results: Volume measurements overestimate volume, more so for thicker slices. For the largest balls, the error is 60% for 5-mm slices and 20% for 1.25-mm slices. Effective diameter calculated from volume better approximates actual diameter. For area measurements, errors are 0% to 5% for the largest balls, and the effective and actual diameters are closely matched. Conclusions: Below 5 mm in diameter, changes in volume should reach 100% for reliable indication of growth. Above 6 mm, the threshold for detecting change is on the order of 25% growth. Even under ideal conditions, results indicate the need for caution when making a diagnosis of malignancy on the basis of volume change.

MRI yields cross-sectional image acquisition in multiple planes with very high contrast resolution. Additionally, in MRI of the breast, evaluation of the entire implant is possible. Not only is MRI very sensitive to loss of implant integrity and rupture, but also MRI can evaluate and characterize adjacent fluid collections or soft-tissue masses. Anatomic relationships of abnormalities and normal structures are well seen. In some situations, MRI may offer clinically relevant information not adequately addressed by other imaging modalities.

Rationale and objectives Low-field magnetic resonance imaging (MRI) evaluation of breast implants is described, with emphasis on the capabilities provided by different imaging sequences. Methods Open architecture MR images using a .064-T permanent magnet and three-dimensional Fourier transform and inversion recovery sequences were obtained. A breast coil was designed and built for this project. Symptomatic and asymptomatic patients with silicone, saline-silicone and saline implants, and phantoms were part of this study. Phase images were used to differentiate protons in silicone, water, and fat. Results and conclusions Low-field MRI permitted differentiation of silicone, water, and fat. Implant anatomy and surrounding pathology could be imaged and identified.

In disorders which involve the bone marrow, the fat/water ratio of the marrow is often an indicator of the progress of disease. A noninvasive method of monitoring this ratio in bone marrow could be clinically useful. We have investigated a method of bone marrow assessment, using magnetic resonance imaging at low field (0.064 Tesla). The method has been tested using calibrated phantoms; we also present results from normal human subjects.

Room temperature semiconductors are potentially attractive candidates for gamma cameras because of their compactness and high spatial resolution. We have evaluated position-sensitive HgI2 detectors for use in high resolution small area gamma cameras. Two 0.5 mm thick detectors resolved by orthogonal strips into elements 1.75 mm on a side and 0.9 mm on a side have been tested. The spatial resolution is 2 mm FWO.1M and 1 mm FWO.1M respectively. Energy resolution is improved by measuring energy from the anode in coincidence with the cathode signal of the detector. An energy resolution of 6.8 keV FWHM at 122 keV and 5.7 keV FWHM at 60 keV has been observed.

A high purity germanium gamma-camera has been developed and is currently being evaluated. This camera incorporates unique performance parameters such as a 2 mm full-width spatial response function with rejection of multiple-scatter in the detector, a 2.2% FWHM energy resolution for 99 mTc, a 180 nsec paralyzable dead-time, and a 2 mu sec non-paralyzable dead-time. Imaging studies demonstrate the superior capabilities of this instrument.

Positron tomography utilizing conventional detector technology realizes images with a spatial resolution that is from 5 to 15 times worse than the spatial resolution achieved in x-ray computerized tomography (CT). The inherently high contrast of radionuclide images (when compared to CT) is then lost, especially when small lesions are sought. A preliminary evaluation indicates that semiconductor detectors offer the potential to yield high sensitivity, high spatial resolution, fast devices capable of imaging over clinically significant areas.

Advances in technology make it possible to extend the range of physical and chemical tissue parameters used for formation of images. This in turn adds to the capabilities to diagnose disease and assess its extent. Quantitative improvements in instrumentation augment the fidelity with which the imaging is performed, and at a certain point provide a quantum jump in diagnostic capability. We discuss recent technological advances in digital radiography, NMR and nuclear medicine imaging that demonstrate these effects.

Computational techniques allow the simulation of NMR images as well as the construction of tools for evaluating the impact of changing parameters. Use of these tools assumes the acquisition of a minimal set of patient data from which the tissue properties T1, T2 and hydrogen density H, can be taken. Changes in technique, imaging parameters such as TE, TR or TI, and field can be simulated and examined individually as well as concurrently for their effects on the contrast between a lesion and its surrounding tissue. This evaluation is done by plotting the absolute difference in signal intensities as a function of the imaging parameters of the technique. Retrospective calculations of intensity images at new values of the pulse timing parameters may show improved diagnostic utility.

NMR imaging of rats with implanted hepatomas in the liver demonstrates that under the imaging conditions of this study tumors of over 8 mm2 in area can be detected with high accuracy. Compared to normal liver, approximately 70% of these tumors had a combination of relaxation times (T1-T2) that could be uniquely identified as tumors, while the other 30% demonstrated relaxation time combinations that overlapped those previously found for abscesses, brain, and hematomas.

A germanium gamma-camera has been interfaced to a conventional x-ray CT computer obviating the need for a separate camera control console. The computer provides all the functions of hardwired consoles (including the persistence oscilloscope), and increases the flexibility of the system. Updated images are available on a real time basis, and a high quality display provides reliable transcription of images onto Polaroid or transparent film.

Cardiovascular research uses the microsphere technique as a tool to measure regional blood flow. Although the technique is extremely powerful, the instruments used to assay the microspheres limit the number of different tracers that can be used in one animal to 5 or 6. As is often the case, many more measurements per animal are needed, and the limitation necessitates using many more animals per experiment. This in turn increases costs and decreases the quality of the data, since no animal is its own control for the full set of experiments. A large germanium well counter designed for microsphere work has been evaluated. The detector is 9.8cm long, 5.7cm in diameter, with a 2.1cm well bore. The useable well has a 1.5cm diameter and reaches to within 2cm from the far end of the detector. Energy resolution ranges from 3 keV FWHM at 100 keV to 5 keV FWHM at 500 keV. Detector performance matches well that predicted from Monte Carlo calculations. The counter will increase the research utility of the microsphere technique in a cost-effective manner.

Human images of excellent quality have been obtained with Nuclear Magnetic Resonance (NMR), using two different techniques: projection reconstruction (PR) and two-dimensional Fourier transformations (2DFT). It has been shown in CT that the reconstruction algorithms will multiply the noise in the projections and change the noise spectrum. A comparison of the noise of the two techniques is presented under the constraint of equal imaging conditions using both computer simulations and data obtained with the UCSF human imager. The computer simulations show that the two techniques produce approximately equal signal to noise values when S/N ~ 15. Below that value small differences are observed. For both simulations and actual data, the 2DFT shows a uniform spatial frequency response while the PR method shows a roll-off at low spatial frequencies. The 2DFT method is shown to be more resistant to artifact formation.

A multiwire proportional chamber positron camera consisting of four 48 × 48 cm2 detectors linked to a small digital computer has been designed, constructed, and characterized. Initial clinical application to brain imaging using 68Ga DTPA in 10 patients with brain tumors is described. Tomographic image reconstruction is accomplished by an algorithm determining the intersection of the annihilation photon paths in planes of interest. Final image processing utilizes uniformity correction, simple thresholding, and smoothing. The positron brain images were compared to conventional scintillation brain scans and x-ray computerized axial tomograms (CAT) in each case. The positron studies have shown significant mitigation of confusing superficial activity resulting from craniotomy in comparison to conventional brain scans. Central necrosis of lesions observed in the positron images, but not in the conventional scans, has been confirmed in CAT. Modifications of the camera are being implemented to improve image quality, and these changes combined with the tomography inherent in the positron scans are anticipated to result in images superior in information content to conventional brain scans.

A technique is described for obtaining tomographic images of hydrogen distribution in animals using nuclear magnetic resonance (NMR). Resonant frequency is proportional to magnetic field strength, so that spatial resolution is achieved by frequency selection and magnetic field shaping. The results of scanning a phantom and two rats are presented.

The use of a high purity germanium gamma camera capable of assigning the interaction point of a gamma-ray unambiguously to a 2×2mm2 element, together with the use of matched square-hole tantalum tube collimators, permits the application of a weighted backprojection technique to reconstruct images that do not show the loss of spatial resolution associated with distance between the object and collimator surface. The technique converges, and images with improved definition are obtained.

A gamma-ray camera consisting of two 3.2×3.2×1-cm3 HPGe detectors has been assembled. Shallow orthogonal grooves define 512 2×2-mm2 elements. Square hole collimators have been fabricated with design parameters that exploit the unique characteristics of the detector. Intrinsic spatial resolution is a square function with 2-mm width, and energy resolution is approximately 2.5% FWHM at 140 keV. Evidently superior images are obtained when this instrument is compared to state-of-the-art scintillation cameras.

Principal component analysis (PCA), a common tool from multivariate statistical analysis, has been implemented into the computer display system of a MR imaging device. PCA allows the calculation of images in which the information in a defined region of interest inherent in the basic acquired images is condensed. PCA image calculation has been applied to acquired MR studies of 13 patients with brain lesions. The appearance of the brain lesions on the resultant PCA images was scored in comparison to the acquired images before and after administration of Gd-DTPA as well as to other calculated images including T1, T2, hydrogen density, and contrast-optimized images. The conspicuity of a lesion and the number of distinguishable components within a lesion were slightly superior on PCA than on the acquired images. PCA is an analytical tool for MR imaging that should be helpful in revealing information that is inherent in, but not readily visible on, standard acquired MR images.

The sequence of radiofrequency and magnetic field gradients used to form an NMR image produces changes in the signals emitted by moving blood when compared to the signals from stationary blood. These changes can be used to measure the open area of vessels. In addition, specific relaxation time signatures of lesions may help in identifying the nature of the obstructions.

The imaging capabilities of the germanium camera, (high spatial resolution and scatter rejection) combined with processing to recover loss of resolution at depth, have resulted in single-photon emission tomography with significant improvement in spatial resolution when campared to devices based on conventional technology. Multiple radionulides can be imaged, and spatial resolution of 2-4 mm at depth can be realized.

The availability of semiconductor detectors, principally High Purity Germanium, permits consideration of new generations of nuclear medicine imaging devices. These are characterized by excellent spatial resolution and by simultaneous multiple radioisotope imaging capabilities. The technology and some of its resultant benefits are presented here.

The multiparametric nature of NMR imaging allows the same section to be displayed in many different ways by either adjusting acquisition parameters or calculating additional images, creating a possibly overwhelming data set. The need for this many images may be reduced by creating tissue type maps where each tissue is identified according to its characteristic NMR parameters and painted using a color code. Although T1 and T2 values for normal tissue are reproducible, variability among patients, the wide range of T1,T2 and N(H) values for abnormal tissue and partial volume averaging make the determination of tissue signatures difficult without significant operator intervention. A hierarchical processing algorithm, pyramidal segmentation, allowing simultaneous analysis at multiple levels of spatial resolution provides the basis for a tissue mapping algorithm with significantly reduced operator supervision.

A programme was written to detect flow in a sequence of MR images and to construct 3-D vessel maps from the detected flow regions. Reduction in first echo intensity and prolongation of calculated T2 value were used as flow-detection criteria. The programme was used to image the aorta in 6 patients with abdominal aortic aneurysm and 5 patients with aortic dissection. Results were compared with contrast angiography in 9 cases and X-ray CT in 2. The images obtained by the two techniques were comparable in 9 cases. In 2 cases of aortic dissection, where flow in the false lumen was slow, the false lumen could not be demonstrated by angiography, but was clearly seen in the reconstructed MR images.

MRI is a powerful diagnostic modality of expanding availability. Equipment and installation amount to nearly $2M per site. An important component of diagnostic efficacy is not just equipment costs but also replacement costs, which for x-ray CT amount to 14-20% of the purchase cost per year; and in the early years of that technology reached 30-50%. We show how design choices made during the R&D stages of MRI development have allowed us to improve system performance parameters such as data reconstruction, archiving and display speeds, computational capabilities, operator interfaces, imaging sequence flexibility and signal-to-noise levels. Over the last four years these improvements have been made at a retrofit cost well below our target of 6-7% of the purchase price per year.

This paper describes an MRI technique which can be used to acquire images at short TR values while maintaining the sensitivity to disease found in longer TR images. For spin echo imaging there are three acquisition parameters that can be set in the imaging protocol; TR, the repetition interval; TE, the time of echo and THETA, the excitation flip angle. Standard imaging techniques set THETA to 90 degrees regardless of the TR value. With THETA fixed, imaging systems have been optimized by varying the value for TE and TR with the results in general indicating the need for long TR values. However, if the flip angle is included as a variable acquisition parameter the optimal operating point can be changed. The solution to the Bloch equation shows a functional relationship between the flip angle and the ratio TR/T1. This functionality was first observed by Ernst and Anderson as a method to increase the signal generated in fourier transform magnetic resonance spectroscopy. When TR/T1

FEA is being used in medicine to substitute radiotracers and chemical analysis of stable tracers. Excitation with polarized x-rays reduces tracer working levels: Since they scatter at preferential angles they reduce the number of photons reaching the detector, thus decreasing system dead time and background. The use of a 160KV 19mA x-ray tube for FEA of iodine (and neighboring elements) realizes count-rates of 2.5 cts/sec/ppmI and background reductions from 11.5 ppmI (when using Am-241 excitation) to 5.7 ppmI. These early results indicate that counting time to realize constant quantitation accuracy can be reduced by 90%. Since the use of the x-ray tube results in a 50% increase in the cost of the source-excited automated system, the ten-fold reduction in analysis time makes this a practical approach.

The non-invasive determination of absolute lung density would be of great importance if it could be used in the evaluation of patients with pulmonary edema. To obtain this measurement, we have developed a a portable densitometer using CdTe room-temperature detectors, compact collimators made of tantalum tubes and a Gd-153 source. System response in the density range of 0.1 to 1 g/cm3 is linear. Variations in the absorption paths of up to 8 cm of lucite do not produce significant changes on measured density values.

Although the basic physics of the NMR process dates back about 40 years, and the demonstration that images could be formed from NMR signals is over a decade old, only recently has NMR imaging come to receive wide attention. Analysis of the hardware of a system shows that success depends less on stressing the state‐of‐the‐art of individual components than on careful engineering design and thoughtful integration of existing technologies.

An automated X-ray fluorescence system with a low Compton background was designed utilizing a metal filter, electronic devices, polarized X-rays for element excitation, a Si(Li) detector, and a commercially available X-ray tube. Rb, Mo, Ag, I, La, and Gd were tested in order to select a single optimal filter. A low Compton background and a high count rate over a wide spectral range were obtained with a filter optimized for Ag. Regions of interest were chosen for K alpha peaks of Zr, Mo, Rh, Ag, Sn, I, and Ba. The net K alpha peak areas were computed by subtracting the K beta counts from the total net counts in the regions of interest. An excellent linear relation was obtained between the computed K alpha net counts and their concentrations. The net count rates (c.p.m./p.p.m.) were 29.34 (Zr), 46.56 (Mo), 69.78 (Rh), 81.60 (Ag), 77.75 (Sn), 70.30 (I) and 74.13 (Ba). It is concluded that all seven elements can be used for nonradioactive microspheres with satisfactory counting statistics for simultaneous measurements of regional blood flows. >

An automated low-background X-ray fluorescence detection system was developed for measuring blood flow rates by the microsphere technique. An X-ray beam was polarized to lower Compton scattering. A Si(Li) detector was used for efficient characteristic X-ray detection with preferentially decreased sensitivity for Compton scattering, a CaF/sub 3/ scintillation detector was engaged in the anticoincidence method to lower the background, and risetime rejection was used for the same purpose. Solutions of 1 cm/sup 3/ each of Rb, Mo, Ag, I, La and Gd with concentration of 0.2-2.0 p.p.m. were measured for 80 min and those of 2.0-20 p.p.m. were measured for 10 min. For Ag the net counting rate was approximately 75 counts/min/p.p.m. The anticoincidence detector lowered the background by 10% in the region of Ag X-rays. The linear relation between net counts and actual element concentration held up to 1000 p.p.m. for Ag solutions. >

NMR imaging is based on the ability to induce and monitor resonance of the magnetic moment of nuclei in the presence of magnetic fields. By the use of magnetic fields whose strength varies with position, it is possible to define both the location and concentration of resonant nuclei, and, thereby to create images that reflect their distribution in tissue. Hydrogen, because it is the most sensitive of the stable nuclei to NMR and because it is also the most abundant nucleus in the body, is ideally suited for NMR imaging.

A proportional chamber employing delay-line readout has been adapted for thermal-neutron imaging through the use of a boron converter plate as one of the chamber electrodes. A small prototype chamber using natural B for a converter has achieved 0.5% thermal-neutron-detection efficiency and better than 2 mm resolution (10% - 90% knifeedge). A converter-plate-model calculation gives good agreement with the measurements and shows how efficiency and resolution vary with chamber thickness, energy discrimination, and B and Alovercoating thicknesses. Substitution of 10B for the natural B would give a five-fold increase in efficiency and the calculations indicate that a further improvement in both efficiency and resolution of up to 50% is achievable in a single-plate system. The results of these calculations and a comparison with measurements are presented.

We describe multivire proportional chambers (MWPC) designed for use in a positron camera for Nuclear Medicine applications. The coordinates of the two annihilation gamma rays are detected in the chamber by their interaction with thin lead converters placed on both faces of each chamber. In order to obtain reasonable efficiencies (10%) the lead converters have been made in a square honeycomb-like structure, which increases the effective surface area and also permits the application of a drift field to extract the electrons into the active area of the MWPC.

We describe a xenon-filled multi-wire proportional chamber (MWPC) with delay-line readout of coordinates for nuclear medicine applications. This system, with an active area of 30.5 × 30.5 cm2, is being used to image internally administered radioisotope distributions in animals for research purposes.

Spark chambers with digitized readouts offer distinct advantages in spatial resolution and coverage over other gamma-ray imaging devices. While these chambers usually require external logic signals for triggering, in this paper we describe a method that provides self-triggering spark chambers. We also describe initial tests of a 45 × 45 cm spark chamber with 60Co and 198Au samples.

We describe a camera for the laminographic imaging of the thyroid without administration of radiopharmaceuticals to the patient. An external source of gamma-rays is used to excite the characteristic x-rays of natural iodine in the patient's thyroid, source geometry limiting excitation to well-defined planes. The camera consists of a parallel hole collimator and a xenon-filled proportional wire chamber with digitized readout of coordinates. Pulse height selection is provided to limit events in the image display to a selected energy range. We estimate that the system will obtain high resolution laminography for local exposures on the order of 1 to 5 rad, with exposure times of a few minutes for each laminogram.

Some methods by which the applicability of the magnetostrictive delay line readout for wire spark chambers can be extended for use in magnetic field regions are described. For fields up to 20 kG iron-cobalt alloy wires with either a coil or a piezoelectric receive transducer can be used. A different method involving the generation of acoustic pulses in non ferromagnetic wires is described. With a piezoelectric receive transducer this delay line is essentially unaffected by magnetic fields.

The replacement of conventional clinical techniques and the development of new techniques using solid state detectors are discussed. Work presented here includes a simplified (geometry and counting-time independent) method for in-vitro iodine and bromine determinations, in-vivo iodine measurements through a tissue absorption correction based on the ratio of. K? to Ks radiation, cardiac output studies, and evaluation of absorptive characteristics of cerebral ventricles.

Measurement of the clearance of insufflated tantalum and barium sulfate powder from the lung is important in evaluating tantalum as a roentgenographic contrast agent, as well as in the investigation of lung clearance mechanisms. This report evaluates the technique of fluorescent excitation for measuring clearance of particulate tantalum and barium sulfate from the lungs, using a 2-Ci gadolinium-153 (153Gd) source and an 80 mm2 lithium-doped silicon (Si(Li)) detector.

High purity germanium offers excellent potential for use in nuclear medical imaging cameras. A position and energy readout technique using two inexpensive delay lines has been developed for these cameras. Results obtained with a 1-cm2 , 4 mm deep, 5×5 strip high purity germanium detector are 2.1 mm full width spatial resolution, a measured single strip resolution of 0.65 mm full width half maximum (FWHM), a 25 element uncollimated energy resolution of 2.95 keV FWHM, and 2.65 keV FWHM for a single central element at 140 keV.