Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CASSETTE FOR HANDLING AND HOLDING TISSUE SAMPLES DURING
PROCESSING, EMBEDDING AND MICROTOME PROCEDURES, AND
METHODS THEREFOR
Field of the Invention
The present invention generally relates to supports for handling
and embedding tissue samples for pathological analysis and, more
particularly to cassettes which can receive one or more tissue samples and be
embedded and subsequently microtomed with the tissue sample or samples.
Background of the Invention
To accurately diagnose various tissue diseases and conditions,
medical personnel must remove one or more samples of tissue from the body
to a patient. This process of harvesting tissue from the body is known as a
biopsy. Once the tissue sample or samples are removed and sent to a
pathology laboratory, the tissue will go through a series of procedures
performed by a histotechnician and, ultimately, a pathologist, in order to
diagnose the tissue. The present invention generally relates to those
procedures that are normally performed by the histotechnician to prepare the
tissue sample or samples into slides that may be analyzed under a
microscope by the pathologist.
Although the singular term "sample" is used throughout this
specification, it should be understood that this term likewise encompasses
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plural "samples" as well. Once a tissue sample is removed from the body of a
patient, it is typically placed into a specimen container containing a tissue
fixative solution and then the container is transported to a pathology
laboratory.
The tissue will undergo a process known as "grossing-in" in the pathology lab
during which a histotechnician will retrieve the tissue sample from the
container,
typically cut the tissue into appropriate sizes for tissue processing, place
individual samples into the appropriate sized small plastic tissue cassettes,
and
assign tracking numbers to each cassette. These tracking numbers are then
logged into a tracking system used in the laboratory. For the smallest tissue
samples, which may only be scrapings, the cassette will have fine mesh
openings on the sides and bottoms. In other situations involving very small
tissue samples, the samples are placed into a bag that resembles a tea bag
and prevents the smallest tissue samples from escaping. Larger tissue
samples are placed into cassettes having somewhat larger slotted openings
which are again smaller than the tissue sample inside the cassette.
The cassettes are then placed into a stainless steel perforated
basket and run through a tissue processing machine, often overnight. This
machine uses a combination of vacuum, heat, and chemicals to remove the
interstitial fluids. Once the fluids have been removed from the tissue
samples,
the processing machine immerses the tissues samples in a bath of molten
paraffin so that the interstices in the tissue are replaced with paraffin. The
histotechnician then removes the basket from the machine and removes the
individual tissue cassettes. At an embedding station, which has a molten
paraffin reservoir and dispenser, the histotechnician will individually remove
the
tissue from each cassette. The histotechnician must carefully orient the
tissue
sample, based on tissue type, into a stainless steel base mold which is
roughly
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the size of the tissue cassette and is partially filled with molten paraffin.
The
tissue sample must be manually held, typically using forceps, against the
bottom of the mold. If it is not, this could compromise the ability to make
proper
slices of the tissue later in the microtome. The molten paraffin is then
rapidly
cooled on a refrigerated plate, which may be a thermal electric cooler (TEC),
to
partially solidify the paraffin thereby holding the tissue sample in the
proper
orientatibn against the bottom of the mold. The cassette is then placed on top
of the base mold and paraffin is poured through the opened top of the cassette
into the base mold. The cassette changes its function at this point in the
procedure from a tissue holding component to a fixation device for later use
in
taking shavings or slices from the solidified paraffin in a microtome. The
base
mold is chilled until all of the molten paraffin has solidified and the
histotechnician removes the stainless steel base mold from the block of
embedded paraffin. The tissue sample is thus embedded within a rectangular
block of paraffin with a plastic tissue cassette on the opposite side which
will
then be used as a holder in the chuck of the microtome. As with the tissue
processing machine, the embedding process is accomplished in a batch fashion
during which an average histotechnician may embed approximately 40 to 60
cassettes per hour.
The blocks of hardened paraffin containing the embedded tissue
samples are then ready to be sliced into extremely thin sections for placement
on a microscope slide. The histotechnician mounts the embedded tissue block
in a chuck on the microtome which is sized to accept the side of the block
that
has the embedded plastic cassette. The histotechnician can then begin slicing
the paraffin block whiah has the tissue sample embedded opposite to the
plastic
cassette surface. This yields a ribbon of individual slices of the tissue
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embedded in the paraffin. The action of the microtome causes the individual
slices to stick together when done properly and, subsequently, these very thin
ribbons of slices are floated into a water bath and a glass slide is carefully
placed underneath the slice. The slice, with the thin sectioned tissue sample
embedded therein, is then adhered to the top of the slide.
When the histotechnician has enough slides from the tissue
sample, the slides are placed into an automatic staining machine. The staining
machine goes through a series of infiltrating steps to stain the different
tissue
and cells of the slide different colors. This helps the pathologist identify
different structures and makes it easier to find any abnormalities in the
tissue.
After the staining procedure is complete, the slides are cover slipped and
prepared for the pathologist to place under a microscope to analyze.
Based on the summary of the procedure provided above, it will be appreciated
that conventional tissue sample handling and processing is a very labor-
intensive process involving several manual steps performed by a
histotechnician. Thus, repetitive stress injuries such as carpal tunnel
syndrome
are prevalent. This is especially true with the tissue sample embedding
process. These multiple manual operations and repeated tissue handling
increase the likelihood of human error and, moreover, require highly trained
and
skilled histotechnicians to ensure that the tissue samples ultimately adhered
to
the slides for analysis by the pathologist are in an optimum condition and
orientation to make accurate diagnoses.
U.S. Patent No. 5,817,032 (the '032 patent) discloses various
improvements to this area of technology, including new manners of holding
tissue samples during the grossing in, embedding, and microtome or slicing
procedures. More specifically, the '032 patent relates to a tissue trapping
and
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supporting device, which may be a cassette, and which may be cut with a
microtome. When a cassette is used, the tissue sample is immobilized within
the cassette and subjected to the process for replacing tissue fluids with
paraffin. Then, the tissue sample and the cassette are sliced at the same time
for mounting on microscope slides. Because the tissue sample is never
removed from the cassette from the time it is processed in the tissue
processing
machine to the time that it is cut with the microtome, a significant amount of
handling time is saved. Moreover, the chance for human error or tissue loss
due, for example, to dropping the tissue during handling, is significantly
reduced
due to the elimination of separate tissue handling steps. This patent also
generally discusses an automated process which, in conjunction with the novel
tissue cassettes, even further reduces the handling steps during the entire
procedure.
In spite of the various advances made in this field, there is an
increasing need for additional improvements related to further manners to ease
the handling procedures of tissue samples, increasing production capability
and
increasing the quality of the embedded tissue samples and the resulting slices
or ribbons of embedded tissue which will be subject to diagnosis.
Summary of the Invention
The present invention generally provides a cassette for holding a
tissue sample. The cassette includes a body and may also include a lid. The
body comprises a bottom wall and one or more side walls extending upwardly
with respect to the bottom wall to define an interior space for receiving the
tissue sample. In one aspect, a plurality of query points (e.g., sensing
elements) are associated with the body and/or lid and configured to allow an
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automated sensing system to determine at least one characteristic of the
cassette. The characteristic may be size, shape, or some other structural or
functional characteristic. The cassette preferably includes a lid configured
to be
coupled with the body and movable between open and closed positions. A
flange extends along upper portions of at least two of said side walls and the
sensing elements may be located on the flange. The sensing elements can
further comprise holes or other detectable, computer readable characteristics
or
elements. The detection can take place in a contact or non-contact manner.
This inventive aspect can also or alternatively be applied to a frame member
which holds the cassette during processing and/or embedding.
The bottom wall of the cassette body preferably transitions to the plurality
of
side walls with a radiused corner, The bottom wall further includes a
plurality of
holes having shapes which are radially elongate and/or widen in a direction
toward the plurality of side walls generally from a gate or fill location of
the
cassette body in a mold used to manufacture the cassette. Each of these
features can help guide the flow of material for forming the cassette during
an
injection molding process. The holes in the bottom wall are preferably located
generally at the center of the bottom wall and have a teardrop shape and/or
oval shape.
At least two of the side walls are positioned in opposed relation to
one another and the dimension between the opposed side walls varies along
the length of the opposed side walls. This may be the result of angling,
undulating or radiusing the side walls along their length and assists with
making
slices in a microtome more easily. As examples, the side walls may be angled
starting at one end thereof and ending at an opposite end, or starting at a
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location between opposite ends thereof and ending, respectively, at the
opposite ends.
In another aspect, a stop member in the interior space of the
cassette is configured to stop the lid at a minimum distance from the upper
surface of the bottom wall. The stop member may be part of the cassette body
or part of the lid.
In another embodiment, an orientation cassette includes a
plurality of posts extending upwardly from the bottom wall. The posts are
configured to orient the tissue sample therebetween to ensure that the
sections taken with the sample are most appropriate for diagnostic purposes.
The lid receivable in the interior space includes holes for removably
receiving
the posts. The posts are further arranged so as not to be aligned with one
another in a straight line either perpendicular or parallel to any one of the
side
walls. This helps ensure more effective cutting in a microtome and less
dulling
of the microtome blade.
According to one aspect of the present invention there is provided
an apparatus for processing a tissue sample, comprising a cassette for holding
the tissue sample, the cassette formed from a material capable of being
sectioned
in a microtome and including: a body including a bottom wall and at least one
side
wall extending upwardly with respect to the bottom wall to define an interior
space
for receiving the tissue sample, and at least one detectable element on the
cassette for detection by an automated sensing system, the detectable element
representing at least one characteristic of the cassette; and a frame defining
a
space for removably receiving the cassette, the frame adapted to support the
cassette in the microtome during sectioning of the tissue sample; wherein the
at
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,
least one detectable element distinguishes the cassette from a second cassette
that is configured to be removably received in the frame.
According to a further aspect of the present invention there is
provided an apparatus for processing a tissue sample, comprising a cassette
for
holding the tissue sample, the cassette including: a body including a bottom
wall and
at least one side wall extending upwardly with respect to the bottom wall to
define an
interior space for receiving the tissue sample, and a flange extending along
an upper
portion of the side wall, the flange including at least one hole; and a frame
defining a
space for removably receiving the cassette, the frame adapted to support the
cassette in the microtome during sectioning of the tissue sample; wherein the
at least
one hole distinguishes the cassette from a second cassette that is configured
to be
removably received in the frame.
According to another aspect of the present invention there is
provided an apparatus for processing a tissue sample, comprising a cassette
for
holding the tissue sample, the cassette formed from a material capable of
being
sectioned in a microtome and including: a body including a bottom wall and at
least
one side wall extending upwardly with respect to the bottom wall to define an
interior
space for receiving the tissue sample, a lid configured to be coupled with the
body,
and at least one detectable element associated with at least one of the body
or the lid
and configured to allow an automated sensing system to determine at least one
characteristic of the cassette; and a frame defining a space for removably
receiving
the cassette, the frame adapted to support the cassette in the microtome
during
sectioning of the tissue sample; wherein the at least one detectable element
distinguishes the cassette from a second cassette that is configured to be
removably
received in the frame.
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The cassette is preferably movable within the space between a first
position for supporting the cassette during processing of the tissue sample,
and a
second position for supporting the cassette in the microtome.
These and other objectives, advantages and features will
become more readily apparent to those of ordinary skill in the art upon review
of the following detailed description of the preferred embodiments taken in
conjunction with the accompanying drawings.
Fig. 1 is a perspective top view of an illustrative biopsy cassette
constructed in accordance with the invention.
Fig. 1 A is an enlarged view of encircled portion 1A taken from
Fig. 1.
Fig. 1 B is an enlarged top view of the cassette bottom wall
shown in Fig. I.
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Fig. 2 is a perspective bottom view of the biopsy cassette shown
in Fig. I.
Fig. 3 is a sectional view taken generally along line 3-3 of Fig. 1.
Fig. 4 is a sectional view taken generally along line 4-4 of Fig. 1.
Fig. 5 is a sectional view taken generally along line 5-5 of Fig. 1.
Fig. 6 is a perspective top view of an illustrative tissue orientation
cassette constructed in accordance with the invention.
Fig. 7 is a top view of the tissue orientation cassette shown in Fig.
6.
Fig. 8 is a perspective view of a frame member constructed in
accordance with the invention and adapted to carry a cassette.
Detailed Description
Cassette Configuration/Type Sensing
Referring to Figs. 1 and 2, cassette 10 may be used in an
automated embedding apparatus such as the one disclosed in the above
incorporated PCT application serial number PCT/US02/30779. More
specifically, the apparatus can utilize an opto-electronic identification
feature
that allows a robotic system to determine which of at least two types of
cassettes 10 has been extracted from an input basket. The different types of
cassettes 10 may, for example, be of different size or have other differing
characteristics and/or function. A plurality of query points, which may be
holes
12 placed in a flange 14 at the periphery of the cassette body 16, allows an
optical scanner to be used to give a binary signal at each query point on the
cassette 10. Since it is advantageous at this time for all cassettes 10 to use
the
same embedding frame, all cassettes 10 are designed to fit into the interior
of
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the frame with a similar registration in the up and down positions. As
additional
cassette features are developed or customer identification becomes necessary,
for example, a similar sensing feature may be incorporated into the frame
which
receives the cassette 10. This feature may be incorporated into many different
types of cassettes to be used in conjunction with automated machinery.
In co-pending application PCT/US02/30779 a sensor can query
each cassette 10 after it has been removed from the input basket. A robotic
arm moves the cassette 10 in the frame under a single sensor head. This
sensor detects the cassette presence to make certain that the cassette 10 has
not been dropped or improperly grasped from the input basket and is more
specifically detecting a binary (signal vs. no signal) to communicate with the
machine control to proceed to embed the cassette 10. This feature may be
enhanced such that the sensor and control proceed to determine how to
process the cassette 10 based on cassette size, type and/or other parameters.
Other parameters may include the type of base mold and any special heating or
cooling parameters that are necessary for processing and/or embedding a
particular type of cassette. The sensor is used to query each cassette/frame
assembly at each input location of, for example, a plurality of locations
where
the control has been programmed to check for a signal. As mentioned above,
four holes 12 at the corners of the flange 14 are currently used for the input
locations. Center portions 14a, 14b of the cassette flange 14 could be used to
increase the number of possible cassette configurations the machine can
discern. As discussed below, the corner locations of holes 12 allow three
cassette configurations to be detected and includes a redundant routine since
the cassette 10 is symmetrical and could be installed by an operator in two
different orientations within the frame (not shown) which carries the cassette
10
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throughout the process. There must be a high degree of certainty that the
automated machinery has correctly detected and verified the cassette
configuration. Using a redundant sensing area is one way to facilitate
improved
certainty.
The sensor in the preferred embodiment is an emitter/detector
sensor, whereby a sensing light beam (infrared or other color spectrum) is
directed towards a tuned sensor. If the query point is open (e.g., a hole 12
in
the cassette flange 14 is detected) the emitter receives enough signal to
register. If the query point is opaque or diffuse (e.g., no hole 12 detected)
the
tuned sensor will not receive enough light to register a signal. Since the
cassette assemblies are pre-processed in a tissue processor which involves the
use of a paraffin containing solution, there is a possibility of a meniscus of
paraffin blocking one of the sensor holes 12. The sensor holes 12 can be
formed large enough to minimize this possibility.
In addition, the cassette 10 is rectangular with two long sides and
two short sides and, as mentioned, can be installed in the frame in two
different
orientations along the long axis of the cassette10. The sensing configuration
is
designed to take this into account, that is, the configuration allows the
machine
to discern the three cassette types regardless of the orientation of the
cassette
10 in the frame. Each long side supplies enough information to properly detect
the cassette type and the other long side carries redundant information. If
more
than three configurations are required, then additional sensing holes (not
shown) may be placed on either side of the centerline at the edges.
With regard to the actual sensing plan it is as follows for three
possible cassettes:
Large tissue cassette:
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All corners opaque (no holes 12)
Signal: Both sensors off
Biopsy cassette (small cassette) 10:
Opposite corners are opaque (no holes 12), other corners are open (holes 12)
(diagonal symmetry)
Signal: One sensor on, one off (order insensitive)
Orientation cassette:
All corners are open (holes 12)
Signal: Both sensors on
It will be appreciated that many different types of sensing
systems, which involve either a contact or non-contact type sensor, may be
used to carry out the inventive concepts explained above. For example, many
different types of optical sensing systems, magnetic sensing systems, barcode
type systems or RFD type systems may be used to allow proper identification
of the cassette and/or frame or other forms of information retrieval by the
control of an automated embedding and/or processing system. As one
additional example, a frame member 90 is shown in Fig. 8 which includes an
RF1D element 81 embedded therein to allow appropriate embedded information
to be relayed to the control system, for example, of an automated processing
and/or embedding apparatus. The information to be conveyed is also wide
ranging and may include, for example, various diagnostic information, patient
history, tissue sample information, or any other information helpful to the
histologic or pathologic process.
Securement of Cassette Within Frame Member
Referring to Figs. 1 and 8, a plurality of depressions 80, 82 and
84, 86 are formed on the top surfaces of flange 14 along the long sides of
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cassette body 16. A frame member 90 (Fig. 8) is used to carry cassette 10 and
depressions 80,82 and 84, 86 respectively receive projections or tabs 102, 104
and 106, 108. Additional depressions 110, 112 and 114, 116 are formed on the
upper surfaces of flange 14 along the short sides of cassette body 16. These
depressions respectively receive projections or tabs 120, 122 and 124, 126
formed within the frame member 90 The registered tabs and depressions
securely maintain the cassette 10 within the frame member 80 during
processing and embedding operations.
Air Removal During Embedding Process
The tissue embedding process, when performed manually with
conventional cassettes, is subject to steps or technique that dislodge or
reduce
the entrapment of air bubbles in the paraffin (or embedding material) block.
Air
bubbles are detrimental because they can weaken the paraffin block and
subsequent microtome sectioning can "break out" or cleave off the main
paraffin
body. This leaves an inconsistent edge or hole in the "ribbon" of sections
which
must flow successively from the section in the microtome process. This can
result in an unsuccessful ribbon, and poor quality slides for diagnosis. One
way
to lessen the presence of air bubbles is to tap or otherwise rapidly move the
cassette assembly to remove air bubbles. However, with high speed
automated embedding, the machine may not be designed to perform such a
step. Therefore, in locations where air could accumulate the largest possible
holes may be provided to allow the air to escape during the paraffin-filling
step.
Still referring to Figs. 1 and 2, holes 12, 20 in the flange 14 of the
cassette 10
and under the writing surface of the frame are provided to allow air to
escape.
It will be appreciated that sensor holes 12 are therefore dual purpose. These
holes 12, 20 should be large enough to allow escape of air and free of flash
or
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burrs. Obstructions, such as ribs under the flange, may trap rising bubbles.
Stiffening flanges 22 are located on the top side of the flange 14 to
eliminate air
entrapment. Frame member 80 also includes an air escape recess or passage
83 on its inner surface.
Material Flow to Injection Mold Cassettes.
Again referring to Figs. 1 and 2, certain features of the cassette 10
allow for effective injection molding techniques to be used in its
manufacture.
First, the gate for filling the mold of the cassette body 16 and the lid 24
should
have flow runners directly leading to the edges of the cassette sidewalls 26.
In
the bottom wall 28 the cassette body 16, it is best to avoid having areas
where
the tissue will be blocked from the passage of fluids used to process the
tissue.
Although the center 28a of the bottom wall 28 has some avoidable gate section,
the majority of area is covered with flow holes 30. For molding it is
typically
preferable to have solid flow ribs 24a as used for lid 24. In this inventive
aspect, the mold pins for forming central holes 30a (Fig. 1 B) are configured
with
a teardrop shape to direct the flow of the cassette material out to the
sidewalls
26. Other mold pins for forming holes 30b are elongate in shape in a radial
direction toward side walls 26. These shapes help direct cassette material
efficiently away from the gate or fill location (e.g., central area 28a). The
transition area 29 (Fig. 3) from the bottom wall 28 to the ribs 40 which form
the
side walls 26 is radiused to reduce the flow restriction for molding.
Non-linear Side Walls
Figs 1 and 2 also show that the sidewalls 26 are non-linear with
respect to the frame side which also determines the cutting plane of the
microtome. This may mean that the side walls 26 generally angle from an
approximate midpoint 26a thereof, as shown, or that the dimension between
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opposite sidewalls 26 changes due to angling or curving the side walls 26 in
their lengthwise direction. The cassette side walls 26 could, for example,
have
a large radius along their length or undulate with respect to the frame sides.
The objective of this feature is to avoid having a parallel sidewall with
respect to
the frame side to increase microtome slicing efficiency. It will be
appreciated
that many configuration can fulfill this objective.
Minimum Lid Engagement Height
Referring to Figs. 1A, 3 and 4, the lid 24 engages sidewall bumps
or projections 50a, 50b or 50c in order to keep the lid 24 engaged with the
cassette body 16 at the appropriate height against a tissue sample thereby
keeping the tissue sample enclosed and immobilized in the cassette 10 during
processing. With extremely small tissue samples such as biopsy samples
which can, be as small as 1 mm3. The lid 24 should not come down all the way
and crush the fragile biopsy sample. Stops 52 are incorporated into the
cassette
body 16 to keep the lid 24 from closing all the way down on the sample.
Alternatively, such stops could be located on the lid 24. The height of each
stop
52 is about 0.75 mm but can be in the range of about 0.25 mm to about 1 mm
high. Also, the extremely thin cassette bottom wall 28 (preferred to be about
0.38) allows the sample to be trapped but not to have undue compressive
forces so as to cause a detrimental crush artifact to show up in the sectioned
biopsy and subsequent diagnostic slides.
Orientation Biopsy Cassette
Referring to Figs. 6 and 7, an orientation cassette 60 is used to
orient special tissues (not shown) that must be sectioned "on edge". Reference
numerals corresponding to those from the first embodiment, but having prime
marks in Figs. 6 and 7 refer to corresponding elements of structure. Tissue
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such as skin, gal bladder, bladder, etc., needs to be oriented to allow the
pathologist to view a full cross section of the biopsy. These samples can be
quite small, and therefore need to be retained in a cassette with small holes
like
the biopsy cassette 10. The orientation biopsy cassette 60 allows the
histotechnologist to place the tissue in the proper orientation for sectioning
at
the time of gross-in. This predetermined orientation will be maintained
through
the tissue processing and embedding procedures, thus maintaining the proper
orientation to the cutting plane without having to remove the tissue and
reorient
it for sectioning in a paraffin mold. The tissue is placed between upright
posts
62 molded into the bottom wall 64 of the cassette 60. These posts 62 have
been arranged in configurations that take into account average thickness and
lengths of the tissue to be used in the cassette 60. The posts 62 are further
arranged so that they are not directly in line with one another with respect
to
directions either parallel to or perpendicular to the sectioning blade path.
Since
the posts have more plastic material in them than the sidewall ribs 66, they
could cause dulling of a portion of the microtome blade at an undesirable rate
after repeated use. Therefore, the posts 62 are positioned to minimize the
number of posts 62 cut in succession in the same blade pass. The lid 70 of the
orientation cassette 60 has corresponding clearance holes 72 for the upright
posts 62. The tissue is held in place between the posts 62, and the lid 70 is
depressed onto the posts 62 to secure the tissue against movement, just as in
the other tissue trapping cassette configurations disclosed herein, or in the
incorporated applications. There is a small clearance between the lid
clearance
holes 70 and the posts 62 to keep any tissue from escaping from the cassette
60.
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The scope of the claims should not be limited by the preferred
embodiments set forth in the examples, but should be given the broadest
interpretation consistent with the description as a whole.
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