Adiabatic Theorem for Quantum Spin Systems.

The first proof of the quantum adiabatic theorem was given as early as 1928. Today, this theorem is increasingly applied in a many-body context, e.g., in quantum annealing and in studies of topological properties of matter. In this setup, the rate of variation ϵ of local terms is indeed small compared to the gap, but the rate of variation of the total, extensive Hamiltonian, is not. Therefore, applications to many-body systems are not covered by the proofs and arguments in the literature. In this Letter, we prove a version of the adiabatic theorem for gapped ground states of interacting quantum spin systems, under assumptions that remain valid in the thermodynamic limit. As an application, we give a mathematical proof of Kubo's linear response formula for a broad class of gapped interacting systems. We predict that the density of nonadiabatic excitations is exponentially small in the driving rate and the scaling of the exponent depends on the dimension.

A variable torque motor compatible with magnetic resonance imaging.

High magnetic fields used in magnetic resonance imaging (MRI) do not allow the employment of conventional motors due to various incompatibility issues. This paper reports on a new motor that can operate in or near high field magnets used for MRI. The motor was designed to be operational with the MRI equipment and could be used in a rotating imaging gantry inside the magnet designed for dual modality imaging. Furthermore, it could also be used for image guided robotic interventional procedures inside a MRI system if so desired. The prototype motor was developed using magnetic resonance (MR) compatible materials, and its functionality with MR imaging was evaluated experimentally by measuring the performance of the motor and its effect on the MR image quality. Since in our application, namely, single photon emission tomography, the motor has to perform precise stepping of the gantry in small angular steps the most important parameter is the start-up torque. The experimental results showed that the motor has a start-up torque up to 1.37 Nm and rotates at 196 rpm when a constant voltage difference of 12 V is applied at a magnetic field strength of 1 T. The MR image quality was quantified by measuring the signal-to-noise of images acquired under different conditions. The results presented here indicate that the motor is MR compatible and could be used for rotating an imaging gantry or a surgical device inside the magnet.

Animal model for thoracoscopic laser ablation of emphysematous pulmonary bullae.

BACKGROUND AND OBJECTIVE: Thoracoscopic laser techniques have been described for treatment of pulmonary bullae. Clinical application of this procedure has proliferated despite limited data regarding efficacy or optimal techniques. The objective of this study was to develop an animal model for investigating laser treatment of bullous lung disease. STUDY DESIGN/MATERIALS AND METHODS: Sixty-two New Zealand White rabbits (3-5 kg) were injected intravenously with 0.35 cc sterile-filtered Sephadex G-100 beads (1 g/100 cc suspension). Three hours later, rabbits were anesthetized, intubated, and 10 cc 0.7% heat-treated or 1% untreated carrageenan solution was instilled endotracheally into a catheter wedged in a mainstem bronchus. RESULTS: Bullae formed over 4-6 weeks in 33% of the animals treated with 0.7% heat-treated carrageenan, and 90% of animals receiving 1% untreated carrageenan (P < 0.005) as demonstrated by serial thoracoscopy. Thoracoscopy was performed at 6-8 weeks using 5 mm trocars under general anesthesia and mechanical ventilatory support. Animals developed pulmonary bullae ranging in size from 0.5 to 2 cm. Bullae were ablated under thoracoscopic visualization using a CO2 laser with a 4 mm OD rigid probe and short focal length in a defocused mode, or an Nd:YAG laser with a 0.4 mm diameter flexible fiberoptic probe. Animals recovered quickly following thoracoscopy. CONCLUSION: We have successfully developed an animal model for thoracoscopic laser ablation of emphysematous pulmonary bullae. This animal model should be useful in investigating treatment of bullous lung disease in humans.

Analysis of contributing factors to the occurrence of off-focus radiation (OFR).

Off-focus radiation (OFR) has previously been described by many investigators [R. Thoraeus, Acta Radiologica 18, 753 (1937); L. Mallet and R. Maurin, Radiology 48, 628-632 (1947); J. F. Timmer, Medicamundi 19(2), 52-54 (1974); G. U. Rao, Appl. Radiol. 3(3), 45-49 (1974); R. Birch, Br. J. Radiol. 49, 951-955 (1976); W. W. Roeck, AAPM Symposium, 217-247 (1991)]. Off-focus radiation is frequently manifested on radiographs by the appearance of faint images of anatomical structures outside the collimated field of interest, i.e., soft tissues, ear lobes and hair, which we will refer to as "penumbral images." The observable small detail resolution within these penumbral images led to the assumption that minute sources of increased radiation intensity (secondary microfocal spots) must be present outside the area of the primary focal spot. The existence of these multiple secondary microfocal spots has been established and their locations within the area of the anode surface from which the general OFR originates was identified. The number, size, and distribution of the secondary focal spots vary over time and their magnitudes vary widely. The source of the well-focused electron beams creating the spots is attributed to the cold cathode emission principle.

Quantification of coronary arterial calcium by dual energy digital subtraction fluoroscopy.

Clinical studies of the heart with fluoroscopy have shown that fluoroscopic visualization of calcium in the coronary arteries is strongly associated with coronary artery disease. However, fluoroscopic detection is limited by its low sensitivity, which is partly due to the interfering background tissue structures and image quantum noise. Moreover, quantification of the absolute amount of calcium in an arterial segment has not been possible. A real-time dual-energy subtraction technique has been investigated as a possible solution to the above problem. In this energy subtraction technique, the kVp and filtration are switched at 30 Hz. In order to assess the potential utility of this videodensitometric technique to quantitate coronary artery calcium, arterial phantoms and excised segments of diseased human arteries were imaged. The low- and high-energy images were corrected for scatter and veiling glare before subtraction. Calcium measurements were made using the tissue-suppressed energy-subtracted images. The estimated calcium phosphate and ashed weights of the calcified arterial segments (N = 20) were highly correlated (slope = 1.04, Intercept = -0.33 mg, r = 0.92).

Absolute cross-sectional area measurements in quantitative coronary arteriography by dual-energy DSA.

Recent studies have emphasized the limitations of conventional coronary angiography. These limitations include the lack of correlation between the severity of coronary stenosis as estimated from coronary angiograms and the actual severity of stenotic lesions measured in postmortem hearts. As a result, attempts have been made to quantitate luminal dimension more precisely. The application of quantitative digital subtraction angiography (DSA) in the assessment of coronary artery lesion dimension has been limited by cardiac and respiratory motion artifacts. We have reported previously on a motion-immune dual-energy (DE) cardiac mode in which kVp and filtration are switched at 30 Hz. To assess the potential advantages of a videodensitometric technique for quantification of absolute vessel cross-sectional area (CSA), three different quantitative coronary arteriography (QCA) algorithms were compared. The three algorithms under comparison were a videodensitometric (V) algorithm, which does not require any geometric assumption for absolute vessel CSA measurement, and videodensitometric (VC) and edge detection (ED) algorithms, which do require the assumption of circular cross-section for CSA measurements. A cylindrical vessel phantom (0.5-4.75 mm in diameter) and a crescentic vessel phantom, producing 25% to 90% area stenosis, were imaged over the chest of a humanoid phantom. The low- and high-energy images were corrected for scatter and veiling glare before energy subtraction. For CSA measurements in crescentic vessel phantoms, the V algorithm produced significantly improved results (slope = 0.87, intercept = 0.51 mm2, r = .95) when compared to the VC (slope = 1.05, intercept = 4.19 mm2, r = .75) and the ED (slope = 1.57, intercept = 5.21 mm2, r = .60) algorithms.

Videodensitometric determination of minimum coronary artery luminal diameter before and after angioplasty.

Quantitative measurements of coronary stenoses were made from digital coronary angiograms in 19 patients before and after percutaneous transluminal coronary angioplasty (PTCA). Two methods of measurement were compared. Mean stenosis before PTCA was 67 +/- 10% by the edge detection method and 67 +/- 12% by videodensitometry (difference not significant). After PTCA, the mean stenosis was 32 +/- 14% by edge detection and 30 +/- 13% by videodensitometry (difference not significant). In addition, a new method was developed to rapidly calculate the absolute minimum luminal area and diameter by videodensitometry. The minimum luminal diameter before PTCA was 1.0 +/- 0.5 mm and after PTCA increased to 2.4 +/- 0.5 mm (p less than 0.001). The validity of the videodensitometric method was analyzed in a series of Lucite phantom studies, which suggested that when there is an irregular angiographic appearance, the densitometric method may be more accurate than standard edge detection methods. Digital acquisition of coronary angiograms provides a means for rapid application of quantitative analysis during coronary interventional procedures.

Digital coronary roadmapping as an aid for performing coronary angioplasty.

In an attempt to improve visualization of the position of the guidewire and dilatation balloon during coronary angioplasty, a method was developed called digital coronary roadmapping. With this method a digitally acquired coronary angiogram is interlaced with the live fluoroscopic image of the guidewire and balloon catheter. The digital coronary angiogram is superimposed at the same magnification and radiologic projection as the live fluoroscopic image onto the video monitor above the catheterization table. The digital roadmap image thus provides immediate feedback to the angiographer to assist in directing the guidewire into the appropriate coronary artery branch and to help in placement of the balloon so that it straddles the site of stenosis.

Removal of image intensifier veiling glare by mathematical deconvolution techniques.

X-ray images acquired with an image intensifier detector system suffer from veiling glare, a low-frequency degradation described by a point spread function (PSF). The PSF has two experimentally determined parameters unique to a given image intensifier. This information is utilized to deconvolve the degradation from digitally acquired images. Results demonstrate a significant increase in contrast ratio of high-contrast objects after deconvolution and image restoration.

On the relationship of image intensifier contrast ratios measured by two techniques.

In recent years the contrast ratio (CR) has played an important role in the quantitation of imaging performance of X-ray image intensifiers. In practice, one uses either a lead disc or strip for measurement of contrast ratios. A theoretical relationship relating contrast ratios measured by both disc and strip techniques is discussed and experimental results are presented. The theoretical analysis uses the point spread function model to describe veiling glare for an image intensifier. It has been shown that one can predict strip contrast ratios after a determination of the veiling glare point spread function from a measurement of disc contrast ratios.

Detection and quantitation of coronary artery stenoses from digital subtraction angiograms compared with 35-millimeter film cineangiograms.

To assess the ability to detect coronary artery narrowings from computer-acquired angiograms, a panel of 4 observers independently identified and measured focal coronary narrowings from digital subtraction angiograms and compared the results to those obtained from standard 35-mm cine film angiograms. Both cine and digital angiograms were obtained sequentially using selective intracoronary artery injection of standard amounts of iodinated contrast media. Digital images were obtained at 8 frames/s with a 512 X 512 X 8-bit pixel matrix. Modifications in the imaging chain for computer acquisition included a slower pulsed radiographic mode, a progressive scan camera, and initial storage of the images on an 80-megabyte digital hard disk. Postprocessing computer algorithms were used to enhance the unsubtracted digital images; these included single-frame, mask-mode subtraction, vessel boundary edge enhancement, and 4-fold pixel magnification. In 19 patient studies, 32 arteries were reduced more than 25% in diameter according to at least 1 of 4 observers on either the digital or cine film angiograms. There was no significant difference in the mean percent diameter narrowing for all the narrowings between the digital angiograms (53 +/- 31%) and the cineangiograms (52 +/- 31%). In addition, a 2-way analysis of variance yielded no significant difference between the amount of variability in the measurements between the cine film and the digital technique. This similar variability persisted when subsets of patients based on the degrees of stenosis were considered (e.g., only narrowings from 50 to 90% diameter reduction).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the veiling glare PSF in x-ray image intensified fluoroscopy.

A theoretical derivation for the point spread function (PSF) which describes the veiling glare in x-ray image intensifiers (II) is presented. The PSF is dependent on two parameters which can be determined experimentally for a given II. An experimental investigation of the linearity of veiling glare phenomenon is undertaken. The experimental results indicate that veiling glare could be described as a linear process to a high degree of accuracy.

Correlation of 10-milliliter digital subtraction ventriculograms compared with standard cineangiograms.

Left ventriculograms were obtained with the use of 10 ml of contrast media by passing fluoroscopic video images through a video image processor. The low concentration of dye in the left ventricle was enhanced by the technique of mask mode subtraction, and the images were postprocessed to increase visibility by manipulation of the gray scale and contrast levels. These digital subtraction angiograms were compared to standard cineangiograms by means of 40 ml of contrast media. Of 30 patients studied, six (20%) had runs of ventricular tachycardia during the cineangiogram and had to be excluded. In the remaining 24 patients, there was a good correlation between the two techniques for left ventricular end-diastolic volume (r = 0.77, end-systolic volume (r = 0.95), and ejection fraction (r = 0.97). Spatial resolution in the digital studies was adequate to appreciate wall motion abnormalities that were visualized on the cineangiograms. Left ventricular end-diastolic pressure (LVEDP) did not change after the 10 ml injection, but the mean LVEDP rose 6.0 mm Hg after the 40 ml cineangiograms (p less than 0.01). Digital subtraction angiography can be used to obtain left ventriculograms with one-fourth the amount of contrast media and one-fourth the x-ray exposure compared to standard cineangiograms. This technology will permit multiple left ventriculograms to be obtained which, in turn, will allow intervention studies to be performed in the catheterization laboratory.

Digital angiography in assessment of ventricular function and wall motion during pacing in patients with coronary artery disease.

Using digital subtraction angiography, left ventriculograms were obtained with 10 ml of iodinated contrast material in 21 patients both at rest and during atrial pacing. In 15 patients with significant coronary artery lesions (CAD) (greater than 50% diameter narrowing in at least 1 major artery), ejection fraction decreased during atrial pacing from a mean of 62 +/- 14% to 51 +/- 15% (p less than 0.001). In 14 (93%) of 15 patients, ejection fraction decreased or was unchanged during pacing. In 6 patients with chest pain but normal coronary arteries, ejection fraction increased from a mean of 66 +/- 9% at rest to 72 +/- 6% during atrial pacing (p less than 0.01). Ejection fraction increased by greater than or equal to 5% during pacing in 5 of 6 patients with normal coronary arteries. Patients with CAD also had an abnormal response in end-systolic volume during atrial pacing (50 +/- 31 ml at rest versus 47 +/- 24 ml during pacing) compared with patients with normal coronary arteries (46 +/- 16 ml at rest versus 26 +/- 9 ml during pacing; p less than 0.01). The digital ventriculograms demonstrated new or increased wall motion abnormalities during atrial pacing in 4 of 5 patients with CAD who had wall motion abnormalities at rest and in 8 of 10 patients with CAD who had normal wall motion at rest. Moreover, these wall motion abnormalities occurred in myocardial wall segments that were supplied by coronary arteries with significant lesions. Thus, because digital subtraction angiography allows multiple left ventriculograms to be obtained during routine cardiac catheterization, intervention studies such as atrial pacing can be used to obtain a functional assessment of the severity of coronary arterial lesions.

Development of a radiographic chest phantom with disease simulation.

An anthropomorphic chest phantom with realistic disease simulation is described with a review of previously available chest phantoms. The need for subjective image analysis is discussed and compared with the existing physics parameters as a means of evaluating image quality in chest radiology. An introduction to the use of such a radiographically realistic chest phantom with lung parenchymal detail and disease simulation is illustrated.

A highly accurate focal spot camera--laboratory and field model.

A device has been developed to determine accurately and quickly the shape, size, and intensity distribution of an x-ray tube focal spot. The pinhole device weighs only 1 kg and is portable, enabling it to be used either as a field unit or in a laboratory. The special design obviates any risk of irradiation danger to the investigator, or thermal overloading of the x-ray tube under investigation. The degree of accuracy with which the central beam can be located is better than +/-250 micron, well beyond the requirements of the latest NEMA standards regarding dimensional measurements of diagnostic x-ray tube focal spots. A star test pattern picture may be taken instead of the pinhole picture if required. The device is described and areas of application are discussed.

The production of apparent image bifurcation.

It is well known that x-ray focal spots with split-intensity distributions can produce radiographs exhibiting image bifurcations. The authors observed such bifurcations in optical analogue images which were produced with both split- and uniform-intesity focal spots. The bifurcations observed with the split focal spot were real, while those observed with the uniform focal spot were not observed in photometer scans of the object. The authors explain these bifurcations by a consideration of the response function of the eye.

The technique and applications of lymphography.

The technique of radiographic examination by lymphography of normal lymphatic structures regional to the hind limbs is described in the rabbit, dog and rhesus monkey. Radiographic appearances of normal lymph nodes and possible applications to veterinary science are indicated.Normal lymph node microstructure is illustrated using in vivo intralymphatic injection of a brightly colored radiopaque silicone rubber. Angiogenesis in active germinal follicles during the period of an immune response is displayed. Further applications of the casting technique are suggested.