Staging tool for tissue samples and method of staging a tissue sample cassette

ES 2 345 482 T3

DESCRIPTION

Cassette and incorporation assembly, staging devices, and procedures for manipulating tissue samples.

Field of the invention

The present invention relates generally to supports for handling and incorporating tissue samples for pathological analysis and, more particularly, to cassettes which can receive one or more tissue samples and be incorporated and consequently cut with a microtome with the tissue sample (s).

Background of the invention

To accurately diagnose various diseases and tissue conditions, medical personnel must remove one or more tissue samples from a patient's body. This process of removing tissue from the body is known as a biopsy. After removing the tissue sample or samples and sending them to the pathological laboratory, the tissue will go through a series of procedures performed by a histologist and, finally, by a pathologist, in order to diagnose the tissue. The present invention relates generally to those procedures normally performed by the histologist to prepare the tissue sample (s) on slides that the pathologist can analyze under the microscope.

Although the term "sample" is used throughout the description, it should be understood that this term also implies the plural "samples." After removing a tissue sample from a patient's body, it is typically placed within a specimen container containing a tissue fixing solution and the container is then transported to a pathology laboratory. The tissue will go through a process known as "grossing-in" in the pathology laboratory, during which a histologist will retrieve the tissue sample from the container, typically cut the tissue into pieces of adequate size to process the tissue, place the individual samples inside of the appropriate reduced-size plastic tissue cassettes, and will assign registration numbers to each cassette. These registration numbers are then uploaded to a registration system used in the laboratory. For smaller tissue samples, which may just be tears, the cassette will have precise mesh openings on the sides and bottom. In other situations involving very small tissue samples, the samples are placed inside a bag similar to a tea bag and it prevents the smaller tissue samples from slipping out. Larger tissue samples are placed inside cassettes that have larger slotted openings that are smaller than the tissue sample inside the cassette.

The cassettes are then placed inside a perforated stainless steel basket and run through a tissue processing machine, often overnight. This machine uses a combination of vacuum, heat, and chemicals to remove interstitial fluids. After the fluids have been removed from the tissue samples, the processing machine immerses the tissue samples in a bath of molten paraffin so that the interstices of the tissue are replaced by paraffin. The histologist then removes the basket from the machine and removes the individual tissue cassettes. At an incorporation station, which has a reservoir and a molten paraffin dispenser, the histologist will individually remove the tissue from each cassette. The histologist must carefully orient the tissue sample, depending on the tissue type, into a stainless steel base mold that is approximately the size of the tissue cassette and is partially filled with molten paraffin. The tissue sample must be held manually, typically using forceps, against the bottom of the mold. Failure to do so could jeopardize the ability to make proper tissue portions next on the microtome. The molten paraffin is rapidly cooled on a cooling plate, which may be a thermal electric cooler (TEC), to partially solidify the paraffin thus keeping the tissue sample in a proper orientation against the bottom of the mold. The cassette is then placed on top of the base mold and the paraffin is poured through the open top of the cassette into the base mold. The cassette changes its function at this point in the process, from being a component to enclose the tissue to a fixation device for later use when taking scrapes or pieces of solidified paraffin in a microtome. The base mold is cooled until all of the molten paraffin has solidified and the histologist removes the stainless steel base mold from the embedded paraffin block. The tissue sample is embedded within a rectangular paraffin block with a plastic tissue cassette on the opposite side that will then be used as a support on the microtome plate. With this tissue processing machine, the incorporation process is accomplished in batches during which a histologist can incorporate approximately 40 to 60 cassettes per hour.

The hardened paraffin blocks containing the embedded tissue samples are then prepared to be cut into extremely thin sections in order to be placed on a microscope slide. The histologist mounts the embedded tissue block in a dish on the microtome that is dimensioned to accept the side of the block that has the embedded plastic cassette. The histologist can then begin to cut the paraffin block that has the embedded tissue sample opposite the plastic cassette surface. This produces a ribbon of individual tissue portions embedded in the paraffin. The action of the microtome causes the individual portions to come together when done correctly and consequently these very thin portion ribbons float in a water bath and a glass sheet is carefully placed below the portion. The portion, with the fine tissue sample sectioned and incorporated therein, is then adhered to the top of the portion.

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When the histologist has enough tissue sample portions, the portions are placed in an automatic staining machine. The staining machine goes through a series of infiltration stages to stain the different tissues and cells of the different colors of the portion. This helps the pathologist to identify different structures and makes it easier for any abnormalities in the tissue to be carried out. When the staining procedure is complete, the portions are covered and prepared for the pathologist to place under the microscope for analysis.

Based on the summary of the process described above, it will be appreciated that conventional tissue sample handling and processing is a labor intensive process involving various manual steps that must be performed by a histologist. Therefore, occupational overuse injuries such as carpal tunnel syndrome are common. This is especially true with the tissue sample incorporation process. These multiple manual operations and repeated manipulation of tissue increase the likelihood of human error and also require highly experienced and professional histologists to ensure that tissue samples that are ultimately adhered to the portions for analysis of the pathologist are in optimal condition and orientation to make an accurate diagnosis.

US Patent No. 5,817,032 (the '032 patent) describes several improvements in this area of ​​technology, including new ways to hold tissue samples during grossing-in, incorporation, or the microtome or portioning processes. More specifically, the '032 patent relates to a device for catching and supporting tissue, which can be a cassette, and can be cut with a microtome. When using a cassette, the tissue sample is immobilized within the cassette and exposed to the process to replace tissue fluids with paraffin. The tissue sample and cassette are then cut at the same time to mount 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 it is cut with the microtome, a significant amount of time is saved. In addition, the possibility of human error or tissue loss due to, for example, tissue dropping during handling, is significantly reduced due to the elimination of separate tissue handling steps. This patent also generally deals with an automated process which, together with the new tissue cassettes, further reduces the handling steps throughout the process.

Despite the different advancements made in this field, there is a growing need for further improvements related to increasing production capacity and increasing the quality and consistency of the incorporated tissue samples and the resulting portions or tapes of tissue. incorporated that will undergo diagnosis.

US5928934 describes a cassette that includes an open container with a bottom wall, two side walls, a front wall, and a rear wall. The bottom wall has a plurality of first openings arranged in the wall for the passage of liquid through the cassette in a direction orthogonal to the plane of the bottom wall. At least two of the other walls also have a plurality of second openings for the passage of liquid through the cassette in a direction parallel to the plane of the lower wall. Each of the side walls, the rear wall, and the front wall are disposed at an angle outside of the bottom wall. All openings in the inner bottom, top and side walls of the cassette have a dimension of no more than about 0.5mm. Each of the first openings and the second openings can have any suitable shape such as round, oval, square or rectangular as long as the longest dimension of the opening is less than about 0.5mm. Another feature of the invention is that the walls comprising the lower wall openings are arranged at an inner angle from the inner base of the lower wall.

The present invention provides a cassette for enclosing a tissue sample comprising a body including a lower wall and a plurality of side walls extending upward from said lower wall to define an interior space that receives the tissue sample, in the that at least two of said side walls are positioned in an opposite relationship to each other, said bottom wall and said plurality of side walls being constructed of a material capable of being sectioned in a microtome, and wherein the dimension between said opposite side walls varies along the length of said opposite side walls.

Generally the invention relates to a cassette for holding a tissue sample during an incorporation and cutting process by microtome or portion cutting. The cassette includes a body with a bottom wall and a plurality of side walls that extend upward from the bottom wall to define an interior space that receives the tissue sample. The bottom wall and the plurality of side walls are made of a material capable of being sectioned on a microtome. Preferably, the cassette material is also resistant to any type of degradation during the process that would compromise its ability to function according to the invention. In a first preferred feature of the invention, the plurality of side walls comprise first and second side walls on opposite sides of the bottom wall, each including portions that create an angle from approximate midpoints of the first and second side walls toward the bottom walls. other first and second side walls on the opposite side of the bottom wall. In the preferred embodiment, the two longest sidewalls of the four sidewalls comprising a rectangular cassette are generally V-shaped in a direction away from the interior of the cassette. This presents an apex of the V-shape to the microtome blade, after the embedding process is complete, which aids the cutting action. Specifically, this feature has been found to reduce or prevent the hardened paraffin from breaking or cracking the cassette side wall material while cutting at the microtome.

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The cassette preferably includes a lid configured to engage the body for movement between the open and closed positions. The cap can be pressed down on top of the tissue sample inside the cassette. The lid is preferably stiffer than the bottom wall of the cassette. This feature allows the lid to position the tissue sample in the cassette parallel to the bottom of the mold during the embedding process. More specifically, the more rigid cap presses the tissue sample and the more flexible bottom wall of the cassette against the rigid bottom of a base mold, while the molten paraffin solidifies. This helps to ensure that the bottom wall of the cassette can be completely removed during a microtome operation prior to cutting the tissue sample, and that the tissue is positioned flat against the bottom wall of the cassette.

In another preferred feature of the invention, the side walls of the cassette are perforated such that there is at least about a 2.5: 1 ratio of open area to solid material area whereby the solidified paraffin occupies the open area of the side walls. This ratio can be altered by using different cassette materials and / or paraffin incorporation media. For example, a higher molecular weight wax or a lower molecular weight cassette will allow the ratio to vary somewhat. Currently, a standard industrial paraffin (eg, Sakura VIP processing / incorporation medium) works best with a ratio of at least about 3.0: 1, and more preferably at least about 3.5: 1. This reduces the amount of cassette material that the microtome blade must cut when picking up the tissue portions and thus increases the blade life and the quality of the resulting taped embedded tissue samples. Furthermore, this ratio ensures that the paraffin is strong enough not to fracture when cut by the microtome blade. Another feature that results in similar advantages involves forming side walls from projections and biasing the projections of one of the first and second side walls from those of the opposite side wall along the length of the side wall. Thus, the microtome blade will come into contact with a more uniform amount of cassette material along its length during each pass. This significantly reduces wear on the blade during cutting of the cassette material. Reducing blade wear is beneficial in controlling blade costs as most blades are single use.

In another preferred feature of the invention, the cassette further includes a flange that extends along upper portions of at least two of the side walls. The flange includes depressions configured to mate with retainers in a frame during the tissue incorporation process. This increases the effective height dimension of the interior of the cassette, thus allowing more tissue to be placed in the cassette and more to pass into the microtome. In this regard, each pass of the microtome can take only a 5-micron portion. Therefore, the use of depressions with a depth of, for example, 0.14 ", can allow approximately 70 more portions to be taken in the microtome.

Different unique assemblies of two or more of the tissue cassette, frame and base mold are also described. Regarding the frame and base mold, for example, a structure is provided to physically hold the frame against the base mold. In the embodiment referred to, a seal is provided to perform this holding function and also to prevent leakage of liquid paraffin from the base mold.

Another preferred embodiment provides a device for staging a tissue sample cassette from an upper position in a frame used during an incorporation process to a lower position in the frame. The device includes a lever, a staging mechanism coupled to the crank and configured to be attached to an upper surface of the cassette, and a stopper operatively coupled to the crank and configured to stop vertical movement of the staging mechanism when the cassette reaches a position. bottom in the frame. The staging mechanism further comprises a plurality of fingers that are configured to be attached to a corresponding plurality of locations on the upper surface of the cassette. For example, four fingers can be provided to engage four angular locations on the cassette. This helps to ensure that the cassette engages at least four pairs of teeth located near the angular portions of the cassette thereby positioning the bottom wall of the cassette parallel to and against the bottom wall of the base mold.

In one embodiment, the staging device is a rigid member and the stop comprises a fixed stop member in motion engaged with the staging mechanism and configured to stop against an upper surface of the frame. In another embodiment, the device includes a stabilization mechanism coupled with the handle and movable relative to the staging mechanism. The stabilization mechanism is configured to engage an upper surface of the frame as the mechanism moves the cassette from the upper position to the lower position within the frame. In this embodiment, the staging mechanism is normally spring biased into an upward position and is forced downward against the bias spring during movement of the cassette from the upper position to the lower position. The stopper in this embodiment further includes respective surfaces of the crank and stabilization mechanism that engage with each other when the staging mechanism has positioned the cassette into the lower position. The staging devices of this invention ensure that the cassette is fully mounted within the base mold, and at the same time ensure that the cassette is not pushed too far from the frame. Furthermore, the staging devices ensure that the lower wall of the cassette, and hence the tissue sample, is extended against the lower wall of the base mold. This improves the efficiency and quality of the tissue scrapes made later on the microtome.

Various methods of using the tissue cassette and the cassette / frame / base mold assemblies are also described.

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These and other objects, advantages, and features of the invention will be more readily understood by those skilled in the art from the following detailed description, when considered in conjunction with the accompanying drawings.

Brief description of the drawings

Figure 1 is an enlarged perspective view of an assembly including the tissue cassette, the frame into which the cassette is inserted, and the base mold into which the frame and the cassette assembly are inserted.

Figure 2 is an assembled perspective view of the tissue cassette, frame, and base mold.

Figure 3 is a cross-sectional view taken along line 3-3 of Figure 2 showing the tissue cassette in its initial upper position.

Figure 4 is an assembled perspective view, similar to Figure 2, but showing the staging position of the tissue cassette.

Figure 5 is a cross-sectional view taken along line 5-5 of Figure 4 showing the staging tissue cassette in its second lower position against the bottom of the base mold.

Figure 6 is a cross-sectional view of the frame and the tissue cassette assembled in a material such as paraffin, after being released from the base mold.

Figure 7 is a perspective view of a manual spring biased staging device.

Figure 8 is a longitudinal cross-sectional view of the staging device of Figure 7 being used for staging of a tissue cassette through the frame and into the base mold.

Figure 9 is a perspective view of a tissue cassette constructed in accordance with a second embodiment of the invention;

Figure 10 is a cross-sectional view taken along line 10-10 of Figure 9.

Figure 11 is a perspective view of a manual staging device constructed in accordance with a second embodiment.

Figure 12 is a bottom perspective view of a staging device associated with the staging device of Figure 11.

Detailed description

Referring first to Figures 1-3, a tissue cassette 10 constructed in accordance with the invention is received within a frame 12 and the tissue cassette 10 and frame 12 are positioned in a base mold 14. Following a staging operation, Base mold 14 is subsequently filled with liquid paraffin, as described below. The tissue cassette 10 includes a perforated body 20 formed by four side walls 22a, 22b, 22c, 22d and a bottom wall 24. Each wall is preferably constructed with perforations or openings 26 and projections 28. An upper flange 30 surrounds and extends outwardly from the respective side walls 22 ad.

A lid 32 is coupled to the body 20 by a hinge 34 that allows vertical movement of the lid 32 within the interior of the body 20 to retain one or more tissue samples against the bottom wall 24. The lid 32, likewise, is formed of perforations 36 which can be elongated and generally separated by projections 38. As best shown in Figure 1, elongated perforations 2, 36 in bottom wall 24 and cap 32 respectively extend into central areas 24a, 32a of bottom wall 24 and cap 32. This helps to allow a mold (not shown) is filled with material, such as PFA, during the cassette 10 molding process.

The lid 32 has a shape along its circumference equal to the shape of the side walls 22ad. In this regard, the respective length side edges 40a, 40b of the cap 32 are V-shaped and each includes a tab 42a, 42b generally in the central portion thereof. This in turn corresponds to the V-shape of the length of the side wall 22a and the opposite side wall 22c. Thus, when the built-in tissue cassette is then placed in a microtome and the sections are cut from the built-in tissue cassette, the microtome blade will initially come into contact with the apex corresponding to side wall 22a or 22c, depending on which side is facing the microtome. This has been found to increase the quality of the taped portions made from the built-in tissue cassette. That is, the paraffin will not break or will break very little at the paraffin / cassette interfaces.

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Frame 12 more specifically includes an open interior 50 that receives cassette 10, and an angled front wall 52 that can be used to record indicia, such as patient data. The respective upper and lower seal assemblies 54, 56 and 58, 60 extend into the open interior 50 of frame 12. Initially, the tissue cassette 10 is held between the upper pairs of retainers 54, 46 by pressing the upper flange 30 down past the upper set of retainers 54 and against the lower set of retainers 56, after one or more samples of tissue has been placed within the cassette body 20 and the lid 32 has been closed. The respective retainers 61 extend inwardly from the side walls 22 ad to allow the lid 32 to be snapped closed and retained in a closed position. During a staging operation, the tissue cassette 10 will move vertically and down through the frame 12 until the flange 30 passes the retainers 58 and rests against the retainers 60 in a lower position (FIG. 5). The recesses 62,64 are formed in at least two opposite side walls to allow the fingers of a gripper mechanism to coincide with the assembly during automatic handling and incorporation operations, as necessary. Preferably, the side walls 66a, 66b contain these recesses 62, 64, while the additional side walls 66c, 66d may include additional structure that allows automatic manipulation, or allow other functions as required. Base mold 14 includes an open interior 70 to receive frame 12 and may be surrounded by a resilient elastomeric closure 72 that prevents the escape of liquid paraffin during the incorporation process. This eliminates the additional step of removing excess hardened paraffin from frame 12 after the embedding process has been completed. Such excess paraffin can prevent the frame from fitting properly in a microtome dish.

When comparing Figures 2 and 3 with Figures 4 and 5, it will be appreciated that during the staging process, the tissue cassette 10 moves vertically downward within the interior 70 of the base mold 14, such that the bottom 24 of the tissue cassette 10 comes into contact with the lower part 74 of the base mold 14. In this position, the flange 30 of the tissue cassette 20 is received between the respective retainers 58, 60, holding it in its lower position. Frame 12 preferably is frictionally fitted and held within base mold 14 by one or more resilient fasteners 72. Fastener 72 performs two functions in this embodiment. First, it physically holds the frame 12 within the base mold 14 by friction. This prevents the frame 12 and the attached cassette 10 from floating or otherwise moving while the base mold 14 is filled with paraffin. Second, it prevents liquid paraffin from escaping from the base mold 14 in the area between the outer walls 12a of the frame 12 and the interior 70 of the base mold.

14. It will be appreciated that a different fastener element of the seal 72 may be used in place of physically holding the frame 12 against the base mold 14. In this case, the seal 72 may not be necessary. For example, such fasteners can be clamps, latches, spring elements, or weights. In these figures, the tissue sample (s) within cassette 10 have been erased for clarity. However, it should be understood that the cap 32 will recess into one or more tissue samples 80 contained within the cassette body 20 (FIG. 6). While the assembly of cassette 10, frame 12, and base mold 14 are in the staging configuration shown in Figures 4 and 5, liquid paraffin is introduced through the open interior of frame 12 and through perforations 26, 36 of cassette 10 within interior 70 of base mold 14. The liquid paraffin is then preferably cooled in a suitable cooling device, such as a TEC, and the tissue cassette assembly 10, frame 12, embedded tissue sample 80, and hardened paraffin 82 are removed from base mold 14 as shown. shown in Figure 6. The frame 12 can be used as a device to fix the assembly on a microtome plate and the portions are taken from the bottom surface 82a of paraffin 82. Initially, a blade is used to remove the initial paraffin layer 82 and the bottom wall 24 of the tissue cassette 10. At this point, a different microtome blade can be used to take the taped or scratched portions of the tissue sample 80 and the paraffin around 82 and the side walls 22 ad of the tissue cassette body. Often the same blade used for orienting can also be used for sectioning.

Figures 7 and 8 illustrate one type of staging device 100 that can be used in conjunction with the tissue cassette 10, frame 12, and base mold 14 described above. The staging device 100 includes a crank 102 at an upper end and a staging mechanism 104 at a lower end. Staging mechanism 104 is coupled to a hollow cylinder 106 extending upwardly within a housing 108 rigidly connected to crank 102. A plurality of four stabilization elements 110 are rigidly coupled to cylinder 106, while A plurality of preferably movable staging fingers 112 are coupled to a rocker shaft 114 that extends through cylinder 106.

Shaft 114 is rigidly connected to crank 102 and is biased therein in an upward position by a spring 116 positioned between a lower surface 102a of crank 102 and an upper surface 106a of cylinder 106.

Thus, it will be appreciated that stabilization elements 110 can be positioned against an upper side of frame 12 for stabilization purposes and crank 102 can be lowered downward as indicated by arrow 118.

This moves oscillating axis 114 and attached staging fingers 112 down against tissue cassette 10, thereby moving tissue cassette 10 relative to frame 12 from its upper position shown in Figure 3 to its lower, staging position shown. in Figure 5. To prevent cassette 110 from being pushed too far through frame 12, surface 108a stops against surface 110a when flange 30 reaches its lower position between retainers 58, 60.

Figures 9 and 10 illustrate a second embodiment of a tissue cassette 120. The tissue cassette 120 includes a cassette body 122 having four side walls 124a-d surrounding an open interior bonded on one side.

ES 2 345 482 T3 lower by a lower wall 126. The side walls 124a-d are formed of projections 128 separated by perforations 130 and the lower wall 126 is formed of projections 132 separated by perforations 134. The projections 128 of the side wall 124a they are often offset in a longitudinal direction relative to the projections 128 of the opposite side wall 124b, as shown by distance "d" in FIG. 10. The distance "d" can vary, however, in this embodiment, on average, by about 0.015 "to 0.030". The protrusions 128 that protrude in this way ensure that a microtome blade passing through the walls 124a and 124b comes into contact with a more uniform amount of cassette material along its length. This leads to longer blade life, more uniform blade wear, and higher quality, higher consistency of embedded tissue portions. The protrusions 132 and perforations 134 extend in their longitudinal direction toward a central area 126a of the bottom wall 1216. In this preferred embodiment, the side walls 124a-d are made such that the ratio of plastic cassette material, such as PFA, up to the area formed by the perforations 130 is approximately 3.7: 1. To achieve at least this ratio in the preferred embodiment, the protrusions 128 have a width w1 of about 0.010 "to 0.014", while the perforations 130 have a width w2 of about 0.040 "to 0.050". This perforated area, which is below the solid side wall portion 136, is the area that will be cut with a microtome upon incorporation of the tissue sample 80 (Figure 6). Especially when using PFA with a Shore hardness of 48 to 55 as the material for cassette 120, in conjunction with the above mentioned industry standard paraffin incorporating material, this ratio of cassette material in open area has been found to improve. the quality of the cuts made through the built-in cassette and increases the life of the blade significantly. Depending on the respective molecular weights of the incorporation material and the cassette material, this ratio can be increased or decreased.

A flange 140 surrounds the upper side of cassette body 122 and contains respective upwardly facing depressions 142a, 142b, 142c, 142d. A number of downwardly facing depressions 142e, 142f (only two are referred to) are also contained in flange 140. These depressions respectively coincide with at least retainers 54, 56 and 58, 60 of frame 12 (see Figures 3 and 5). It will be appreciated that additional bottom retainers may be formed in frame 12 to provide additional support and prevent cassette 10 from being pushed too far through frame 12. In such event, additional depressions are formed in the bottom of flange 140 to accommodate additional support retainers. The depressions allow for effective outward extension of cassette body 120 from frame 12 which increases with increasing number of portions to be taken from the cassette incorporated in a microtome. This can be important in many situations to obtain the desired portions for the pathological examination.

Retainers 144 are also formed in side walls 124a-d to retain a lid 150 in place. The lid 150 is attached to the cassette body 122 by a hinge 152. The lid 150 is made to be stiffer than the bottom wall 126 of the cassette body 122 so that the lid 150 can be used to press the sample of tissue against bottom wall 126 and pressing bottom wall 126 against rigid bottom 74 of base mold 14 (FIG. 5). Cap 150 is formed by a plurality of projections 154 spaced generally by perforations 156 and each extend elongated along its entire length toward a central area 150a of a cap 150. Cap 150 further includes side edges 158a, 158b that intersect. They extend the entire length thereof and are V-shaped with a central apex 160a, 160b. The angle a (Figure 10) is preferably about 4 °. As in the first embodiment, the shape of the side edges 158a, 158b has a similar shape to the side walls 124a, 124b of the cassette body 122. In this regard, these side walls 124a, 124b, the initial wall of one of them may be cut at the microtome, include respective apices 162, 162a. The respective ends 164a, 164b of the lid 150 also complement the similar shape of the cassette body sidewalls 124c, 124d to achieve a perfect closure of the lid 150 within the cassette body 122. The use of cassette 120 in the process of incorporating one or more tissue samples, including the staging process within frame 12 and the process of incorporating or molding within base mold 14, is the same as previously described in reference to Figures 1-8.

Figures 11 and 12 illustrate a manual staging device 200 according to a second embodiment. The staging device 200 comprises an upper handle 202 and a lower staging mechanism 204 rigidly coupled by a shaft 206. In FIG. 12, the handle 202 and shaft 206 have been erased for clarity. Staging mechanism 204 preferably comprises a plurality of staging elements 210, 212, 214, 216 that extend generally radially outward from axis 206 and each includes a finger portion 210a, 212a, 214a, 216a. Finger portions 210a.216a respectively engage the angular portions of cassette 10 (FIG. 1) or cassette 120 (FIG. 9). When the user pushes the handle 202 down, the finger portions 210a -216a drive the cassette 10 or cassette 120 down into the lower, staging position (FIG. 5). To prevent the cassette from moving too far down, a pair of stops 218, 220 are provided on the staging mechanism 204. In this embodiment, abutment surfaces 218a, 220a stop against the upper surface of frame 12 when cassette 10 or cassette 120 reaches the lower, staging position (FIG. 5). Thus, the distance between the lower ends of the finger portions 210a-216a and the abutment surfaces 218a, 220a equals the distance between the upper pair of retainers 54, 56 and the lower pair of retainers 58, 60. It will be appreciated that other forms of staging mechanisms and caps can be provided without departing from the spirit and scope of the invention.

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References cited in description

This list of references cited by the applicant is only intended to aid the reader and is not part of the European patent document. Although the utmost care has been taken to carry them out, errors or omissions cannot be excluded and the EPO declines any responsibility in this regard.

Patent documents cited in the description • US 5817032 A [0008] · US 5928934 A [0010]