Viva Questions in Oral Pathology
A single stop for all basic viva questions that you might encounter in your oral Pathology and microbiology paper in your Dental undergraduate course. If you have questions to suggest/add, kindly mail it to me at oralpathology.viva@gmail.com. You will be acknowledged. Every effort is made to ensure the accuracy of the answers. Kindly use textbooks to confirm. Circulate the links widely..
Saturday, 16 May 2015
Monday, 26 May 2014
Experience Documented.....
ORIGINAL ARTICLE | |
|
Use of blog as a supplementary study material resource in dentistry: An Indian experience
Thavarajah Rooban, Arunachalam Mohandoss Anusa
Marundeeshwara Oral Pathology Services and Analytics, Tiruvanmiyur, Chennai, Tamil Nadu, India
Thavarajah Rooban, Arunachalam Mohandoss Anusa
Marundeeshwara Oral Pathology Services and Analytics, Tiruvanmiyur, Chennai, Tamil Nadu, India
Date of Web Publication | 15-May-2014 |
Correspondence Address:
Thavarajah Rooban
Marundeeshwara Oral Pathology Services and Analytics, CS4, Bay Breeze Duraisamy Apartments, 119, East Coast Road, Tiruvanmiyur, Chennai - 600 041, Tamil Nadu
India
Thavarajah Rooban
Marundeeshwara Oral Pathology Services and Analytics, CS4, Bay Breeze Duraisamy Apartments, 119, East Coast Road, Tiruvanmiyur, Chennai - 600 041, Tamil Nadu
India
DOI: 10.4103/0975-8844.132586
Abstract |
Objective: Social networking sites (SNS) are emerging as an alternate teaching resource. The reach and access characteristics of SNS for a noninstitutional, academic blog in an Indian setting has not been documented and this manuscript aim to address this lacunae.Materials and Methods: A blog for oral histology, an integral basic dental subject and its Facebook promotional page was created. The access characteristics were observed using Google analytics. The Facebook promotional pages of the blog access characteristics are presented. Results: A total of 582 people visited the blog during the study period. Majority of them used Google Chrome from desktop/laptop to access the blog. There were 2723 page visits in all. Visitors from 36 countries and 99 cities across the globe accessed the blog. In all through Facebook, the promotional page reached 36,543 people. The total number of people engaged through Facebook promotion page was 10,757. Conclusion: Access characteristics of the noninstitutional, academic blog have been described for the first time in dentistry. The lessons learnt through this exercise would be helpful in designing e-mentoring courses as well promotional pages of such events in the future. The necessity of making the mentors and students to adapt to e-learning and digital learning resources before drawing such programs is highlighted.
Keywords: E-learning and Facebook, Google, Indian blog, oral histology and tooth morphology, oral histology dental blog
Read the full manuscript @ HERE
Thursday, 27 February 2014
Know your tool - Microscope
Image distance and object distance.
With respect to the principal planes of a lens, the image-to-lens and
object-to-lens distances, as predicted by the lens equation in geometrical
optics. See also Lens equation.
Immunofluorescence microscopy. A mode
of fluorescence microscopy in which a certain molecular species in a specimen
is labeled with a specific fluorescent antibody. Fluorescence emission from
excited antibodies is collected by the objective lens to form an image of the
specimen. Antibodies can be made fluorescent by labeling them directly with a
fluorescent dye (direct immunofluorescence) or with a second fluorescent
antibody that recognizes epitopes on the primary antibody (indirect
immunofluorescence).
Incandescent lamp. A bulb containing an
inert gas and metal filament that emits photons as the filament becomes excited
during passage of electric current. The spectrum of visible wavelengths emitted
by the filament shifts to increasingly shorter wavelengths as the amount of
excitation is increased. The output of incandescent lamps is very high at red
and infrared wavelengths.
Infinity corrected optics. The latest
optical design for microscope objective lenses in which the specimen is placed
at the focal length of the lens. Used by itself, the image rays emerge from the
lens parallel to the optic axis and the image plane is located at infinity. In
practice, a tube lens or Telan lens located in the body of the microscope acts
together with the objective to form an image in the real intermediate image
plane. This optical design relaxes constraints on the manufacture of the
objective lens itself and allows for placement of bulky accessory equipment
such as fluorescence filter cubes in the space between the objective and the
tube lens.
Intensity of light. Qualitatively, the
brightness or flux of light energy perceived by the eye. By universal
agreement, the term intensity, meaning the flow of energy per unit area per
unit time, is being replaced by the word irradiance, a radiometric term
indicating the average energy (photon flux) per unit area per unit time, or
watts/meter2. As a term describing the strength of light, intensity is
proportional to the square of the amplitude of an electromagnetic wave.
Interference. The sum of two or more
interacting electromagnetic waves. Two waves can interfere only if a component
of the E vector of one wave vibrates in the plane of the other wave. Resultant
waves with amplitudes greater or less than the constituent waves are said to
represent constructive and destructive interference, respectively.
Interference color. The color that
results from removal of a band of visible wavelengths from a source of white
light.
Interference filter. A filter made from
alternating layers of different dielectric materials or layers of a dielectric
material and thin metal film that transmits a specific band of wavelengths. The
spacings between the layers of one-quarter or one-half wavelength allow constructive
interference and reinforce propagation through the filter of a particular
wavelength λ. All other wavelengths give destructive interference and are
absorbed or reflected and do not propagate through the filter.
Ion arc lamp. Lamps containing an ionized
gas or plasma between two electrodes that radiates visible wavelengths when
excited by an electric current. Arc lamps used in light microscopy usually
contain mercury vapor or xenon gas.
Irradiance of light. The
radiometrically correct term for light intensity. Irradiance is the radiant
flux incident per surface unit area and is given as watts/meter2. Irradiance is
a measure of the concentration of power.
Isotropic. In describing the optical
properties of an object or propagation medium, having identical properties in
different directions.
Jablonski diagram. A diagram showing
the energy levels occupied by an excited electron in an atom or molecule as
steps on a vertical ladder. Singlet and triplet excited states are shown
separately as ladders standing next to each other.
Koehler illumination. The principal
method for illuminating specimens in the light microscope, whereby a collector
lens near the light source is used to focus an image of the light source in the
front aperture of the condenser. The microscope condenser is focused to position the conjugate image of
the light source in the back focal plane (diffraction plane) of the objective
lens. The method provides bright, even illumination across the diameter of the
specimen.
Lens equation. In geometrical optics,
the equation 1/f 1/a 1/b describing the
relationship between the object distance a and the image distance b for a lens
of focal length f.
Light microscope. A microscope
employing light as an analytic probe and optics based on glass lenses to
produce a magnified image of an object specimen.
Linearly polarized light. A beam of
light in which the E vectors of the constituent waves vibrate in planes that
are mutually parallel. Linearly polarized light need not be coherent or
monochromatic.
Long-pass filter. A colored glass or
interference filter that transmits (passes) long wavelengths and blocks short
ones.
Long working distance lens. An
objective lens having a working distance many times greater than that of a
conventional objective lens of the same magnification. A long working distance
lens is sometimes easier to employ and focus, can look deeper into transparent
specimens, and allows the operator greater working space for employing
micropipettes or other equipment in the vicinity of the object. However, the NA
and resolution are less than those for conventional lenses of comparable
magnification.
Lumen. A unit of luminous flux equal to
the flux through a unit solid angle (steradian) from a uniform point source of
1 candle intensity.
Lux. A unit of illumination equal to 1
lumen per square meter.
Modulation contrast microscopy (MCM). A
mode of light microscope optics in which a transparent phase object is made
visible by providing unilateral oblique illumination and employing a mask in
the back aperture of the objective lens that blocks one sideband of diffracted
light and partially attenuates the 0th-order undeviated rays. In both MCM and
DIC optics, brightly illuminated and shadowed edges in the three-dimensional
relief-like image correspond to optical path gradients (phase gradients) in the
specimen. Although resolution and detection sensitivity are somewhat reduced
compared with DIC, the MCM system produces superior images at low
magnifications, allows optical sectioning, and lets you examine cells on
birefringent plastic dishes.
Monochromatic. In theory, light
composed of just one wavelength, but in practice, light that is composed of a
narrow band of wavelengths. Owing to Heisenberg’s uncertainty principle, true
monochromatic light does not exist in nature. Even the monochromatic emission
from a laser or an excited atomic source has a measurable bandwidth. Therefore,
while the light produced by a narrow bandpass interference filter is called
monochromatic, this is just an approximation.
Multi-immersion objective lens. An
objective lens whose spherical aberration is corrected for use by immersion in
media of various refractive indices, including water, glycerin, and oil. A
focusable lens element used to minimize spherical aberration is adjusted by
rotating a focus ring on the barrel of the objective.
Multiple fluorescence filter set. A
filter set for simultaneous viewing or photography of multiple fluorescent
signals. The transmission profile of each filter in the set contains multiple
peaks and troughs for the reflection and transmission of the appropriate
excitation and emission wavelengths as in a conventional single-fluorochrome
filter set. Because of constraints on the widths of bandwidths, the steepness
of transmission profiles, and the inability to reject certain wavelengths, the
performance is somewhat less than that of individual filter sets for specific
fluorochromes.
Negative colors. Colors resulting from
the removal of a certain band of visible wavelengths. Thus, white light minus
blue gives the negative color yellow, because simultaneous stimulation of red
and green cone cells results in this color perception. Similarly, the mixture
of cyan pigment (absorbs red wavelengths) and yellow pigment (absorbs blue
wavelengths) gives green, because green is the only reflected wavelength in the
pigment mixture.
Negative lens. A lens that diverges a
beam of parallel incident rays. A simple negative lens is thinner in the middle
than at the periphery and has at least one concave surface. It does not form a
real image, and when held in front of the eye, it reduces or demagnifies.
Negative phase contrast. In phase
contrast optics, the term applies to systems employing a negative phase plate
that retards the background 0th-order light by /4 relative to the diffracted
waves. Since the diffracted light from an object is retarded /4 relative to the
phase of the incident light, the total amount of phase shift between background
and diffracted waves is 0 and interference is constructive, causing objects to
appear bright against a gray background.
Neutral density (ND) filter. A light-attenuating
filter that reduces equally the amplitudes of all wavelengths across the
visible spectrum. The glass substrate contains light-absorbing colloids or is
coated on one surface with a thin metal film to reduce transmission. Neutral
density filters are labeled according to their absorbance or fractional
transmission.
Nipkow disk. In confocal microscopy, a
thin opaque disk with thousands of minute pinholes, which when rotated at high
speed provides parallel scanning of the specimen with thousands of minute
diffraction-limited spots. The return fluorescence emission is refocused at the
same pinhole in the disk, which provides the same function in rejecting
out-of-focus light as does a single pinhole in a conventional confocal
microscope. Nipkow disk confocal microscopes produce a real image that can be
inspected visually or recorded on a high-resolution CCD camera, whereas images
of single-spot scanning microscopes are reconstructed from signals from a PMT
and are displayed on a computer monitor.
Numerical aperture (NA). The parameter
describing the angular aperture of objective and condenser lenses. NA is
defined as n sin, where n is the refractive index of the medium between the
object and the lens, and , the angle of light collection, is the apparent half-angle
subtended by the front aperture of the lens as seen from a point in the
specimen plane.
Objective lens. The image-forming lens
of the microscope responsible for forming the real intermediate image located
in the front apertures of the eyepieces.
Optical path length. In wave optics, a
measure of the time or distance (measured in wavelengths) defining the path
taken by a wave between two points. Optical path length is defined as n t, where n is the refractive index and t
indicates the thickness or geometrical distance. A complex optical path
composed of multiple domains of different refractive index and thickness is
given as n1t1 n2t2 .
. . niti.
Optical path length difference. The
difference in the optical path lengths of two waves that experience refractive
index domains of different value and thickness. In interference optics,
differences in optical path length determine the relative phase shift and thus
the degree of interference between 0th-order and higher-order diffracted waves
that have their origins in a point in the object.
Optovar. A built-in magnification
booster lens that can be rotated into the optical path to further increase the
magnification provided by the objective by a small amount.
Ordinary ray or O ray. In polarization
optics, the member of a ray pair that obeys normal laws of refraction and whose
velocity remains constant in different directions during transmission through a
birefringent medium. See also Extraordinary ray.
Paraboloid condenser. A high numerical
aperture condenser for dark-field microscopy having a reflective surface that
is a segment of a figure of revolution of a parabola. The steeply pitched
illumination cone produced by the condenser is suitable for darkfield
examination with high-power oil immersion objectives.
Parfocal. The property of having the
same distance between the specimen and the objective turret of the microscope.
With parfocal lenses, one can focus an object with one lens and then switch to
another lens without having to readjust the focus dial of the microscope.
Particle wave. In phase contrast and
other modes of interference microscopy, the wave (P wave) that results from
interference between diffracted and surround waves in the image plane, and
whose amplitude is different from that of the surrounding background, allowing
it to be perceived by the eye. See also Diffracted wave and Surround wave.
Phase contrast microscopy. A form of
interference microscopy that transforms differences in optical path in an
object to differences in amplitude in the image, making transparent phase
objects appear as though they had been stained. Surround and diffracted rays
from the specimen occupy different locations in the diffraction plane at the
back aperture of the objective lens where their phases are differentially
manipulated in order to generate a contrast image. Two special pieces of
equipment are required: a condenser annulus and a modified objective lens
containing a phase plate. Because the method is dependent on diffraction and
scattering, phase contrast optics differentially enhance the visibility of
small particles, filaments, and the edges of extended objects. The technique
allows for examination of fine details in transparent specimens such as live
cells.
Phase gradient. In interference
microscopy, the gradient of phase shifts in an image corresponding to optical
path differences in the object.
Phase object. Objects that shift the
phase of light as opposed to those that absorb light (amplitude objects) as the
basis for image formation. See also Amplitude object.
Phase plate. In phase contrast
microscopy, a transparent plate with a semitransparent raised or depressed
circular annulus located at the rear focal plane of a phase contrast objective.
The annulus reduces the amplitude of background (0th order) waves and advances
or retards the phase of the 0th-order component relative to diffracted waves.
Its action is responsible for the phase contrast interference image.
Phosphorescence: The relatively slow (9
s) emission of photons after excitation of a material by light or other
radiation source.
Polar: The common term applied to a
sheet of linear polarizing film (dichroic filter or Polaroid filter) and
particularly to its use as a polarizer or analyzer in producing and analyzing
polarized light.
Polarizability. In polarization optics,
a property describing the strength of interaction of light with molecules in a
manner that depends on the orientation of atomic bonds. Light waves interact
more strongly with molecules when their E vectors are oriented parallel to the
axis defining light-deformable (polarizable) covalent bonds such as the axes of
long-chain hydrocarbon polymers like polyvinyl alcohol, cellulose, and
collagen. This geometry is supported when an incident light ray is
perpendicular to the long axis of the polymer. Interaction of light with
molecules along their polarizable axis retards wave propagation and accounts
for the direction-dependent variability in their refractive index, a property
known as birefringence.
Polarization cross. In polarization
microscopy, the appearance of a dark upright cross in the back aperture of the
objective lens under conditions of extinction with two crossed polars. Ideally,
the back aperture is uniformly dark under this condition, but the
depolarization of light by the curved lens surfaces of the condenser and
objective lenses causes brightenings in four quadrants and hence the appearance
of a cross.
Polarization microscopy. A mode of
light microscopy based on the unique ability of polarized light to interact
with polarizable bonds of ordered molecules in a directionsensitive manner.
Perturbations to waves of polarized light from aligned molecules in an object
result in phase retardations between sampling beams, which in turn allow
interference-dependent changes in amplitude in the image plane. Typically the
microscope contains a polarizer and analyzer, and a retardation plate or
compensator. Image formation depends
critically on the existence of ordered molecular arrangements and a property
known as double refraction or birefringence.
Polarized light. Light waves whose E
vectors vibrate in plane-parallel orientation at any point along the axis of
propagation. Polarized light can be linearly polarized (vibrations at all
locations are plane parallel) or elliptically or circularly polarized
(vibration axis varies depending on location along the propagation axis).
Polarized light need not be monochromatic or coherent.
Polarizer. A device that receives
random light and transmits linearly polarized light. In microscopy, polarizers
are made from sheets of oriented dichroic molecules (Polaroid filter) or from
slabs of birefringent crystalline materials.
Positive colors. Colors that result
from mixing different wavelengths of light. The equal mixture of red and green
wavelengths results in the perception of yellow, a positive color.
Positive lens. A lens that converges a
beam of parallel incident rays. A simple positive lens is thicker in the middle
than at the periphery, and has at least one convex surface. A positive lens
forms a real image and enlarges or magnifies when held in front of the eye.
Positive phase contrast. In phase
contrast optics, the term applies to systems employing a positive phase plate
that advances the background wave by /4 relative to the diffracted wave. Since
the diffracted light from an object is retarded /4 relative to the phase of the
incident light, the total phase shift between background and diffracted waves
is /2 and interference is destructive, causing objects to appear dark against a
gray background.
Principal plane. For a simple thin
lens, the plane within the lens and perpendicular to the optic axis from which
the focal length is determined. Thick simple lenses have two principal planes
separated by an intervening distance. Complex compound lenses may have multiple
principal planes.
Rayleigh criterion for spatial resolution.
The criterion commonly used to define spatial resolution in a lens-based imaging
device. Two point sources of light are considered to be just barely resolved
when the diffraction spot image of one point lies in the first-order minimum of
the diffraction pattern of the second point. In microscopy, the resolution
limit d is defined, d m/1.22 λ/(NAobjective
NAcondenser), where λ is the wavelength of light and NA is the numerical
aperture of the objective lens and of the condenser.
Real image. An image that can be viewed
when projected on a screen or recorded on a piece of film.
Real intermediate image. The real image
focused by the objective lens in the vicinity of the oculars of the microscope.
Refraction. The change in direction of
propagation (bending) experienced by a beam of light that passes from a medium
of one refractive index into another medium of different refractive index when
the direction of propagation is not perpendicular to the interface of the
second medium.
Refractive index ellipsoid and wavefront
ellipsoid. An ellipsoid is the figure of revolution of an ellipse. When
rotated about its major axis, the surface of the ellipsoid is used to describe
the surface wavefront locations of E waves propagating outward from a central
point through a birefringent material. The same kind of figure is used to
describe the orientation and magnitude of the two extreme refractive index
values that exist in birefringent uniaxial crystals and ordered biological
materials.
Relative retardation. In polarization
optics, the relative shift in phase between two waves expressed in fractions of
a wavelength.
Relay lens. An intermediate magnifying
lens in an imaging system placed between the objective and the real
intermediate image. In video, so-called TV lenses increase the magnification of
the image projected on the camera 2- to 8-fold.
Short-pass filter. A colored-glass or
interference filter that transmits (passes) short wavelengths and blocks long
ones.
Simple lens. A lens consisting of a
single lens element and distinct from a compound lens having multiple lens
elements.
Spatial filter. A filter that
selectively manipulates a location in an image such as an aperture in a field
plane of a microscope or a sharpening or blurring filter in image processing.
Spatial frequency. The reciprocal of
the distance between two objects (periods/ distance).
Spatial frequency filter. A filter that
selectively manipulates a location in the diffraction plane in a microscope
(aperture plane masks in modulation contrast microscopy) or a mask applied to
Fourier transforms to manipulate low and high spatial frequency information in
image processing.
Spatial resolution. The resolution of
component features in an image. In optical systems, resolution is directly
proportional to the wavelength and inversely proportional to the angular
aperture. The practical limits on wavelength and angular aperture determine the
limit of spatial resolution, which is approximately one-half the wavelength of
light.
Spectral range. The range of
wavelengths, or bandwidth, under consideration.
Spherical aberration. A lens aberration
typical of lenses with spherical surfaces that causes paraxial rays incident on
the center and periphery of a lens to be focused at different locations in the
image plane. The degree of aberration increases with the decreasing focal ratio
of the lens. The aberration can be corrected in simple lenses by creating
aspherical surfaces.
Stokes shift. The distance in
nanometers between the peak excitation and peak emission wavelengths of a
fluorescent dye.
Thin lens. A lens whose thickness is
small compared to its focal length. A line through the center of the lens (a
plane representing the two coincident principal planes of the lens) provides a
reasonably accurate reference plane for refraction and object and lens distance
measurements. Lenses are assumed to be thin when demonstrating the principles
of graphical ray tracing.
Tube lens or Telan lens. An auxiliary
lens in the body of the microscope, which in conjunction with an infinity focus
objective lens forms the real intermediate image. The Telan lens provides some
of the correction for chromatic aberration, which lessens constraints on the
manufacture of the objective lens.
Uniaxial crystal. A birefringent
crystal characterized by having a single optic axis.
Virtual image. An image that can be
perceived by the eye or imaged by a converging lens, but that cannot be focused
on screen or recorded on film as can be done for a real image. The image perceived
by the eye when looking in a microscope is a virtual image.
Wavelength. The distance of one beat
cycle of an electromagnetic wave. Also, the distance between two successive
points at which the phase is the same on a periodic wave. The wavelength of
light is designated λ and is given in nanometers.
Wollaston prism. In interference
microscopy, a beam splitter made of two wedgeshaped slabs of birefringent
crystal such as quartz. In differential interference contrast (DIC) microscopy,
specimens are probed by pairs of closely spaced rays of linearly polarized
light that are generated by a Wollaston prism acting as a beam splitter. An
important feature of the prism is its interference plane, which lies inside the
prism (outside the prism in the case of modified Wollaston prism designs).
Working distance. The space between the
front lens surface of the objective lens and the coverslip. Lenses with high
NAs typically have short working distances (60–100 micro m). Lenses with longer
working distances allow you to obtain focused views deep within a specimen.
Definitions in Microscopy
Diffraction grating. A transparent or
reflective substrate containing an array of parallel lines having the form of
alternating grooves and ridges with spacings close to the wavelength of light.
Light that is reflected by or transmitted through such a grating becomes
strongly diffracted. Depending on the geometry of illumination and wavelength, a
grating can generate color spectra and patterns of diffraction spots.
Diffraction plane. One of the aperture
planes of the light microscope containing the focused diffraction image of the
object. Under conditions of Koehler illumination, the diffraction plane is
located in or near the back focal plane of the objective lens.
Distortion. An aberration of lenses,
where the magnification factor describing an image varies continuously between
the central and peripheral portions of the image. Depending on whether the
magnification is greater at the center or at the periphery, the distortion can
be of the barrel or the pincushion type, respectively.
Double refraction. In polarization
optics, the splitting of light into distinct O and E rays in a birefringent
material. When a birefringent crystal of calcite is placed on a page of printed words, the effects of double
refraction are clearly observed as an overlapping, double image of the text.
Emission filter. In fluorescence
microscopy, the final element in a fluorescence filter cube, which transmits
fluorescence emission wavelengths while blocking residual excitation
wavelengths. Commonly called a barrier filter. Emission filters are colored
glass or interference filters and have the transmission properties of a
bandpass or long-pass filter.
Emission spectrum. In fluorescence, the
spectrum of wavelengths emitted by an atom or molecule after excitation by a
light or other radiation source. Typically, the emission spectrum of a dye
covers a spectrum of wavelengths longer than the corresponding excitation
spectrum.
Epi-illumination. A common method of
illumination in fluorescence microscopy, where the illuminator is placed on the
same side of the specimen as the objective lens, and the objective performs a
dual role as both a condenser and an objective. A dichroic mirror is placed in
the light path to reflect excitatory light from the lamp toward the specimen
and transmit emitted fluorescent wavelengths to the eye or camera.
Excitation filter. In fluorescence
microscopy, the first element in a fluorescence filter cube and the filter that
produces the exciting band of wavelengths from a broadband light source such as
a mercury or xenon arc lamp. Commonly the excitation filter is a high-quality
bandpass interference filter.
Excitation spectrum. In fluorescence,
the spectrum of wavelengths capable of exciting an atom or a molecule to
exhibit fluorescence. Typically the excitation spectrum covers a range of
wavelengths shorter than the corresponding
fluorescence emission spectrum.
Eyepiece or ocular. The second
magnifying lens of the microscope used to focus a real magnified image on the
retina of the real intermediate image produced by the objective. The added
magnification provided by the eyepiece increases the angular magnification of
the virtual image perceived by the eye. The typical range of eyepiece
magnifications is 5–25.
Eyepiece telescope. See Bertrand lens.
Field diaphragm. A variable diaphragm
located in or near the aperture plane of the light source that is used to
reduce the amount of stray light in the object image. Since the edge of the
diaphragm is conjugate with the object plane under conditions of Koehler
illumination, the field diaphragm is used as an aid in centering and focusing
the condenser lens.
Field planes. That set of conjugate focal
planes representing the field diaphragm, the object, the real intermediate
image, and the retina.
Flat-field correction. In image
processing, the procedure used to obtain a photometrically accurate image from
a raw image. A so-called dark frame containing bias and thermal counts is
subtracted from the raw image and from a “flat” or “background” image. The
dark-subtracted raw image is then divided by the dark-subtracted flatfield
image to produce the corrected image. With operation, all optical faults are
removed. The photometric relation of pixel values to photoelectron count is
also lost during division, although the relative amplitudes of pixel values
within an image are retained. See also Dark frame and Flat-field frame.
Fluorescence. The process by which a
suitable molecule, transiently excited by absorption of external radiation
(including light) of the proper energy, releases the energy as a
longer-wavelength photon. This process usually takes less than a nanosecond.
Fluorescence microscopy. A mode of
light microscopy whereby the wavelengths of fluo-rescence emission from an
excited fluorescent specimen are used to form an image.
Fluorite or semiapochromat lens.
Objective lenses made of fluorite or Ca2F, a highly transparent material of low
color dispersion. The excellent color correction afforded by simple fluorite
elements accounts for their alternative designation as semiapochromats. The maximum numerical aperture is usually
limited at 1.3.
Fluorochrome. A dye or molecule capable
of exhibiting fluorescence.
Fluorophore. The specific region or
structural domain of a molecule capable of exhibiting fluorescence. Examples
include the fluorescein moiety in a fluoresceinconjugated protein and the
tetrapyrrole ring in chlorophyll.
Focal length. The distance along the
optic axis between the principal plane of a lens and its focal plane. For a
simple converging (positive) lens illuminated by an infinitely distant point
source of light, the image of the point lies precisely one focal length away
from the principal plane.
Focal ratio or f-number. The ratio of
the focal length of a lens to the diameter of its aperture.
Fovea. A 0.2–0.3 mm diameter spot in
the center of the macula on the retina that lies on the optic axis of the eye
and contains a high concentration of cone cell photoreceptors for color vision
and visual acuity in bright light conditions.
Frame averaging or Kalman averaging. In
electronic imaging, the method of averaging a number of raw image frames to
reduce noise and improve the signal-to-noise ratio. The signal-to-noise ratio
varies as the square root of the number of frames averaged.
Halo. In phase contrast microscopy,
characteristic contrast patterns of light or dark gradients flanking the edges
of objects in a phase contrast image. Halos are caused by the phase contrast
optical design that requires that the image of the condenser annulus and
objective phase plate annulus have slightly different dimensions in the back
focal plane of the objective.
Huygens’ principle. A geometrical
method used to show the successive locations occupied by an advancing
wavefront. An initial source or wavefront is treated as a point source or a
collection of point sources of light, each of which emits a spherical wave
known as a Huygens’wavelet. The surface of an imaginary envelope encompassing
an entire group of wavelet profiles describes the location of the wavefront at
a later time, t. Huygens’ principle is commonly used to describe the
distribution of light energy in multiple interacting wavefronts as occurs
during diffraction and interference.
Thursday, 20 February 2014
Inking the Specimen
INKING THE
SPECIMEN
·
Various Water/organic fluids insoluable inks and
colored powders can be used to mark critical points on the specimen.
·
These dyes and powders may help orient both the
gross specimen and the histologic section. For example, colored tattoo powder
sprinkled on the outer surface of a cystic mass can be used to distinguish
between the outer and inner aspects of the cavity.
·
Similarly, India ink can be painted on the
surgical margins so that they can be easily recognized at the time of
histologic examination.
·
Indeed, many times the critical distinction of
whether a neoplasm extends to the surgical margin depends entirely on the
absence or presence of ink.
·
Given the important implications of an inked
surface, these inks should be carefully and judiciously applied to the gross
specimen.
·
Keep in
mind that just as the effective use of inks can facilitate the
histologic interpretation, the careless and improper use of these inks can
befuddle the microscopic findings.
·
The implications of sloppily applied ink that runs
across a surface where it does not belong will be disastrous.
·
The following guidelines outline the proper
application of inks:
o
If possible, apply ink before sectioning the
specimen.
o
Do not use excessive ink.
o
Dry the surface of the specimen with paper
towels before applying ink.
o
When applied to a dry surface, ink is more
likely to stick to the desired surface and less likely to run onto other areas
of the specimen.
o
Allow the ink to dry before further processing
the specimen.
o
Do not cut across wet ink, as the knife is
likely to carry the ink onto the cut surface.
Cassette Dimensions
Inside
dimensions for a screened cassette are: 2.5 x 2.0 x 0.3cm
Inside
dimensions for a standard slotted cassette are: 3.0 x 2.5 x 0.3cm
Routine
tissue sections submitted in standard slotted cassettes should be no larger
than 2.5 x 1.5 x 0.3cm to allow for proper processing.
Screened Cassettes
• Distinct
advantages to using screened cassettes with small tissue biopsies;
1.Negates
the need to wrap samples, a big time saver.
2.Positive
seal created when properly closed.
3.Prevents
cross-contamination with other tissues during processing
Cost is a
major Disadvantage
For Small
Biopsies
• Number of
Pieces Each Container - To the best of your ability, give an accurate count.
Check the container (to include the lid!) and req. for a reference to the
number of pieces submitted.
Often
samples are fragmented. In this case, count the number of significant pieces,
give size(s), and add the descriptor “fragmented”. Additional Descriptors for
Number
• Additional
descriptors for number of pieces; Multiple(>10) - Give aggregate dimensions
with average size each. Do not submit more than 5 per cassette. Myriad – too many to count (fragments), give
aggregate dimensions. Filter thru screened cassette.
• State the
size(s) of the tissue(s) received: Always stated in the context of mm.’s or
cm.’s Do not use inches. If you start the case using mm.’s, then use mm.’s
throughout. If you start the case with cm.’s, then use cm.’s throughout. Ex.
0.4cm or 4mm. Whole cm.-Do not use
decimal point and zero.
•
Referencing the size(s) of the piece(s): If only one, self explanatory. If two
or more of the same size, then state as: __ mm. or cm. each. If two of
different sizes, then state as: __ and __ mm. or cm. each.
If three or
more with different sizes, then state as: ranging from __ mm. or cm. to __mm.
or cm.
Cores - • Whenever possible, give exact
count of tissue cores. Not necessary to give the diameter of the cores in most
cases, but always give the length of each core.
• Indicate
formalin exposure times with cores.
Biopsy Tissue Configurations
Irregular
/Fragmented/ Cores/Polypoid/Sessile/Pedunculated
Punch
Biopsies(Derms)- • Elipses(Derms)/• Shaves (Derms)
To Cut or Not To Cut!
• Most diagnostic
cases do not require additional cutting or inking.
• Polyps
>5mm should have their bases inked and be bisected.
• Punch
biopsies >4mm should also be bisected.
Thursday, 13 February 2014
Tissue Sampling Techniques - Small Biopsies & Triaging
Tissue Sampling
Techniques - Small Biopsies & Triaging
Most Important Steps
• Patient
identification - Identification on the requisition must match the container(s).
This includes name. Accession number must match requisition, specimen container
and cassette.
Receiving/Accepting
Specimens
• If you
accept a specimen in the receiving area with incorrect information, it becomes
the laboratories problem to get it back to the sender for correction. Better to
refuse the specimen at the time of delivery.
• Never
process a specimen without a patient name. Never label the container yourself
with patient name or specimen source/type.
GROSS BENCH RULES
• Never have
more than one specimen out at a time.
• Close
containers when leaving the area.
• Don’t
leave small biopsies on the cutting board or on paper towels.
• Keep
cutting area neat, clean and organized.
• Keep
sharps in clear view, not under toweling etc. Clear cutting area of sharps when
leaving, and disinfect the cutting board and countertop.
• Beware of
“carry-over” from case to case
Specimens can be subclassified
Depending
on utility
Diagnostics
specimen
Routines –
Small and Large
Dermatology
Resections
Others
Depending
on Nature of handling:
·
Specimens only requiring transfer from container
to tissue cassette.
o
All small biopsies
o
Bone marrow & Aspirates.
o
Punch biopsies.
o
Needle biopsies
o
Any biopsies not requiring dissection
·
Specimens requiring transfer, but with standard
sampling, counting, weighing or slicing.
o
Sebaceous cysts.
o
Small lipomas.
o
Unremarkable tonsils.
o
Unremarkable nasal polyps.
o
Temporal arteries.
o
Thyroglossal cysts.
o
Lymph nodes.
·
Simple dissection required with sampling needing
a low level of diagnostic assessment and/or preparation.
o
Salivary gland – non-tumour.
o
Cone biopsy.
o
Small soft tissue tumours.
o
Skin biopsies – benign – requiring dissection.
o
Simple small benign biopsies.
·
Dissection and sampling required needing a
moderate level of assessment.
o
Salivary gland – tumours.
o
Pigmented skin lesions.
o
Complex (non-neoplastic) gastrointestinal
resections.
·
Specimens requiring complex dissection and
sampling methods.
o
Bone tumours.
o
Neck dissection.
o
Mandibulectomy.
Diagnostic
• Diagnostic
Cases: Small tissues being submitted to establish a diagnosis or monitor
status.
Typical features of biopsy tissues;
Small in size (minute to ~1cm)
Do not require orientation
Require counting when possible
Often are submitted in “toto”
Currettings
Currettage
specimens come as multiple tissue fragments admixed with; Blood or Blood Clot
/Mucous
Sample EMC
dictation - “Specimen consists of multiple fragments of pink/tan irregular soft
tissue admixed with mucous and blood having aggregate dimensions of _____ x
______ x _____cm which are submitted in toto in a single cassette, levels are
requested.
·
Small specimens should never be forcibly
squeezed between the ends of a forceps or the tips of the fingers. Instead,
small specimens should be gently lifted from the specimen container using the
end of a wooden applicator stick or pickups. Alternatively, small specimens can
be filtered directly into a tissue bag, avoiding instrumentation altogether.
·
Small specimens should be quickly placed in
fixative. Ideally, most small specimens (i.e., less than 1 cm) should reach the
surgical pathology laboratory already in fixative.
·
This requires that physician offices, biopsy
suites, and operating rooms be supplied with appropriate fixatives, and that
all personnel involved be instructed as to their proper use. Sometimes delays
in fixation are necessary, as when a frozen section is required or when special
tissue processing is indicated. In these instances, the tissue should be kept
damp in saline-soaked gauze.
·
Never leave small tissue fragments exposed to
the air on the cutting table, and never place these small fragments directly on
a dry paper towel. These practices are sure to hasten tissue desiccation.
·
For extremely small specimens, the journey from
specimen container to histologic slide is a treacherous one, and they may be
lost at any point along the way. For this reason, it is a wise practice to
identify these small tissue fragments first and then mark the fragments so that
they can be found more easily by the histotechnologist.
·
Before the specimen container is even opened,
check its contents for the size and number of tissue fragments, and record
these in the gross description.
·
If no tissue is seen or if inconsistencies with
the requisition form are noted, carefully open the specimen container and
thoroughly examine its surfaces (including the undersurface of the lid) for
adherent tissue fragments. If no tissue is found or if discrepancies persist,
the submitting physician should be notified immediately, and the outcome of
this investigation should be documented in the surgical pathology report.
·
Once all of the tissue is identified in the specimen
container, efforts should be taken to ensure that it safely reaches the
histology laboratory and that it is easily identified for embedding and
sectioning. Minute tissue fragments should be wrapped in porous paper or
layered between porous foam pads before they are placed in the tissue cassette.
·
Before these fragments are submitted to the histology laboratory, they can be
marked with eosin or mercurochrome so that they are easier for the
histotechnologist to see.
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