Super-resolution and apodization with discrete adaptive optics.

High-resolution imaging is of great importance in various fields. The use of pupil phase-only filters (PPF) exceeds the diffraction limit of the imaging system in a simple way. When dealing with distorted wavefronts, however, PPF require that aberrations be compensated for. In this paper, we introduce a novel technique consisting of the use of discrete adaptive optics with PPFs so that the compensating device implements the PPF at the same time. Analysis of the theory for point spread function reshaping using PPFs has enabled us to develop a new approach to characterizing apodizing filters. A validation experiment has been carried out, the first of its kind to our knowledge, in which a number of PPFs were combined with two levels of compensation. Our experimental results are discussed.

Gastric pyogenic granuloma: Report of two cases and review of the literature.

Pyogenic granuloma (PG) is a polypoid lobular capillary hemangioma rarely described in the stomach. We report two cases aged 72 and 66 years. A review of the literature on gastric PG, including the present cases, yielded ten patients. There were six males and four females. The age of the patients ranged from 35 to 82 years with a mean of 58.9 years. The lesions were all solitary, except one case of multiple lesions in the corpus and antrum. PG can be located in any part of the stomach. The most common site was the antrum. The mean maximum diameter of the lesions was 14.5mm (range 7-30mm). Most lesions were pedunculated. Pain or discomfort (epigastric, right upper quadrant or chest), upper gastrointestinal bleeding, and melena were the most common clinical symptoms. Iron deficiency anemia was the rule, often requiring blood transfusion. Five patients underwent snare polypectomy, four endoscopic mucosal resection, and one laser irradiation. The follow-up ranged from two weeks to two years. There were no recurrences. Pathologists should be familiar with this condition in order to avoid overdiagnosis as a malignant vascular tumor.

Myeloid sarcoma of the extrahepatic bile ducts presenting as obstructive jaundice.

We report a rare case of myeloid sarcoma (MS) of the extrahepatic bile ducts presenting as obstructive jaundice in a patient without leukemia at time of diagnosis. A 75-year-old female presented with a one-month history of abdominal pain and jaundice. Computerized tomography scan of the abdomen showed stenosis of the extrahepatic bile ducts. Endoscopic retrograde cholangiography disclosed an irregular narrowing of the common biliary duct, suggestive of a cholangiocarcinoma, and resection was performed. Histologic examination showed diffuse transmural infiltration of malignant cells. These cells exhibited medium-sized round nuclei with central nucleoli and eosinophilic cytoplasm, and were strongly positive for myeloperoxidase, CD68, lysozyme, CD45, CD117 (c-kit protein) and CD43. Eight months following surgery the patient presented with multiple cutaneous nodules and bone marrow trephine biopsy showed acute myelomonocytic leukemia. A literature search identified two previously reported cases of MS of the extrahepatic biliary duct. MS should be taken into consideration in the differential diagnosis of a patient with obstructive jaundice. Immunohistochemistry is essential for a correct diagnosis.

Pneumopolycystic endometritis.

Emphysematous inflammations of the abdomen and pelvis are uncommon and potentially life-threatening conditions that require aggressive treatment. Pneumopolycystic endometritis is a rare benign condition of which only 1 case has been described. This report describes the sonographic and histologic appearance of pneumopolycystic endometritis in a 49-year-old woman who presented with irregular menses and hypermenorrhea of 1 year's duration. The entity is characterized by gas-filled cysts in the endometrium stroma, in a pattern similar to pneumatosis of the vagina. The histologic picture is specific and should not be confused with gas gangrene involving the uterus characterized by the presence of tissue necrosis and life-threatening infection. Our patient is the first documented case that occurred spontaneously and at the same time was limited to the endometrium. Recognition of pneumopolycystic endometritis is important because this condition does not represent an aggressive life-threatening infection, and spontaneous resolution is to be expected.

Non-Gaussian speckle statistics in adaptive-optics partial compensation.

Wave fronts distorted by the atmosphere can be partially reconstructed by use of adaptive-optics systems. The intensity statistics at the image plane is a function of the ratio D/r(0) and of the level of compensation performed by the adaptive-optics system. We show that a non-Gaussian statistics is obtained when the aperture diameter is slightly greater than the Fried parameter. This situation can frequently be found when one is working in the IR. The light statistics is obtained by use of a simple model to describe the atmosphere and application of the same procedure used in the analysis of scattered light. Special attention is paid to very high- and very low-compensation regimes.

Exoplanet detection using a nulling interferometer.

The detection of extra solar planets is a topic of growing interest, which stretches current technology and knowledge to their limits. Indirect measurement confirms the existence of a considerable number. However, direct imaging is the only way to obtain information about the nature of these planets and to detect Earth-like planets, which could support life. The main problem for direct imaging is that planets are associated with a much brighter source of light. Here, we propose the use of the nulling interferometer along with a photon counting technique called Dark Speckle. Using a simple model the behavior of the technique is predicted. The signal-to-noise ratio estimated confirms that it is a promising way to detect faint objects.

Rician distribution to describe speckle statistics in adaptive optics.

Adaptive optics systems allow us to retrieve high-spatial-frequency information that is preserved in the wave fronts distorted by the atmosphere. Although wave-front correction should be as complete as possible, only partial compensation is attainable in the visible. We provide a procedure that uses the Rician distribution to predict the intensity statistics of the light at the image center as a function of the number of corrected Zernike polynomials.

Speckle statistics in partially corrected wave fronts.

Wave fronts distorted by the atmosphere preserve high-spatial-frequency information. This information can be retrieved by use of adaptive optics systems to correct the incoming wave front. This correction should be as nearly complete as possible. In experiments performed in the visible, only partial compensation is attainable. We provide a theoretical model to predict the intensity statistics of the light in the image center as a function of the number of Zernike polynomials corrected.

Autocorrelation central hole estimates in nonlinear photon-counting detectors.

In an experiment in which two or more photoevents arriving at the same pixel are considered a single count, a one-pixel-size central hole appears in the autocorrelation estimate. This hole is a source of error when high-resolution techniques based on the autocorrelation function are applied to image or signal recovery. We present an experimental method to evaluate the autocorrelation central hole based on the nonlinear behavior of the total number of counts per frame when clipped photocount distributions are considered. The technique is easy to perform and provides high accuracy.

Movement characterization with the spatiotemporal Fourier transform of low-light-level images.

The spatiotemporal Fourier transform of a series of frames is proved to be an attractive technique for object velocity determination. The main disadvantage of the spatiotemporal transform methods is that they require a long processing time even when fast transforms are used. We show that the spatiotemporal Fourier-transform technique, which has been applied to standard-light-intensity images, can also be used with low-light-level images. The result is an important processing time reduction; thus when fast processing is required, it would be advantageous to detect in low-light-level conditions with intensity filters. The technique behavior for low-light-level images is checked with computer-simulated and experimental data.

Autocorrelation evaluation from clipped photon detection.

We present two new techniques for estimating the autocorrelation function, based on the measurement of the mean number of clipped photocounts and on the calculation of the second-order factorial moment of a series of clipped data. The first procedure has the advantage of simplicity, although it produces a poor signal-to-noise ratio. On the other hand, the second technique gives a very good signal-to-noise ratio, when compared with other known methods.

Analysis of techniques for autocorrelation estimates from clipped data.

We analyze a series of techniques for obtaining estimates of the autocorrelation function that canbe applied to clipped data. The direct autocorrelation of clipped data is the simplest technique and provides results that are the same as or better than those from other methods. It is also shownthat it is not possible to obtain the theoretical autocorrelation function of the signal when clipped data are used.

Triple and autocorrelation functions from factorial moments measured.

This research establishes a clear relation between the autocorrelation (AC) and triple-correlation (TC) functions of a signal and its second- and third-order factorial moments (FM's). Theoretical expressions of the variances corresponding to the AC and TC obtained from the measurement of FM's is developed for low-light-level conditions. Experimental values corresponding to direct AC measurements were also compared with those obtained from the FM measurement. The conclusion is that the measurement of FM's may be an alternative to AC and TC measurements.

Evaluation of triple correlation from triggered factorial moment measurement.

Triple-correlation values are obtained as a combination of second-order factorial moments of the triggered photocount distribution. The signal-to-noise ratio obtained from this kind of measurement is smaller than that obtained from direct calculation of the triple correlation for small time-delay values.

Triple correlation of the interval probability density at low light levels.

A Poisson point process presents a series of characteristics that may be used to define functions with a good signal-to-noise ratio. This research describes a statistical function obtained by handling the measured intervals between photopulses and containing the same information about the signal to be analyzed as the triple correlation. This function can be successfully applied to the analysis of low-light-level signals or images.

Characterization of the double-interval probability distribution as a tool for signal or image recovery.

The relation between the double-interval probability distribution P(tau, tau') and the triple-correlation function is shown. This relation allows us, under certain conditions, to obtain the value of the triple correlation of a signal by measuring the photoelectron interarrival times. This procedure is useful in signal or image recovery.