Figure 3(a) is a photomicrograph of a starfish embryo taken with a Nikon Eclipse E600 microscope operating in standard phase contrast mode. The effect of apodized phase plates on images seen in the microscope is illustrated in Figure 3 for two specimens. In apodized phase contrast microscopy, this phase plate replaces the plate on the left at the objective rear aperture. Surrounding the phase film in this plate are two concentric areas of semi-transparent neutral density material, which reduce the intensity of light diffracted from the specimen at small angles. On the right in Figure 2 is an illustration of an apodized phase plate. The purpose of the film is to retard the phase of direct light passing through the specimen by one quarter wavelength to allow constructive and destructive interference with diffracted light at the intermediate image plane. The classical phase plate on the left, which is positioned at the objective rear focal plane, has a thin ring of neutral density material (termed a phase film) applied to the surface (also illustrated in Figure 1). Presented in Figure 2 are a conventional (or classical) and an apodized phase plate positioned at an angle to the viewer and sectioned through the center for ease of illustration. At the intermediate image plane, an interference pattern results, which produces intensities proportional to the phase shift induced by the specimen. The direct background light is attenuated by a neutral density thin film applied to the phase ring in the objective. This is achieved by adding or subtracting a quarter wave shift to the direct light by means of a semi-transparent phase plate strategically placed in a plane that is conjugate (the objective rear focal plane) to the annulus in the condenser (the condenser front focal plane). The phase differences of the direct light from the background and the diffracted light from the specimen cause the two beams to interfere with each other at the intermediate image plane. A small phase shift measuring approximately one quarter wavelength relative to the direct light is induced in the light diffracted by the specimen. Light that passes through the specimen undeviated arrives at the rear focal plane of the objective in the shape of a ring, whereas the fainter light diffracted by the specimen is spread over the entire surface of the focal plane. As the hollow cone of light emanating from the phase annulus encounters the transparent specimen, it is either diffracted by subcellular components and the membrane or passes through undeviated. View the DATABASE results for ' Gibbs Artifact' (4).Light passing through a ring aperture or annulus, mounted in the substage condenser front focal plane, is used to illuminate the specimen in conventional phase contrast microscopy ( Figure 1).See also Gibbs Phenomenon and Apodization. This problem can only be resolved by smoothing filters (LanczosSigmaFactor, 2-D Exponential Filtering, Gegenbauer Reconstruction etc.) or with a higher acquisition matrix and/or a smaller FOV, to smooth the object. the artifact is more intense in the 256 point dimension of a 256x512 acquisition matrix. With more encoding steps the Gibbs artifacts is less intense and narrower. Gibbs artifacts are also seen in other regions, for example the brain//skull interface.įine lines visible in an image may be due to undersampling of the high spatial frequencies, respectively incomplete digitization of the echo. In the spinal cord, a small syrinx can be simulated by the Gibbs phenomenon.
APODIZATION INMR SERIES
This artifact is caused by the Gibbs phenomenon, an overshoot or ringing of Fourier series occurring at discontinuities. This artifact does not occur visibly on smooth objects. The Gibbs or ringing artifact appears as a series of lines in the MR image parallel to abrupt and intense changes in the object at this location. Sharp changes in intensity (incomplete digitization of the echo) Please note that there are different common names for this MRI artifact.
Searchterm ' Apodization' was also found in the following service: Tapering off at higher spatial frequencies so as to reduce ringing artifacts near edges in the corresponding image or spectrum due to truncation and Gibbs phenomenon. The multiplication of acquired MR data by a function smoothly MRI Technician and Technologist Career - Portals - DICOM - Corporations - Education - Collections Result : Searchterm ' Apodization ' found in 1 term and 1 definition 2 3 5 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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