Magnetic field map determination in a magnetic resonance system

Abstract

A method and system for determining a magnetic field map in a MR system based on position of a movable patient support of the MR system are provided, wherein a first resulting field map including position dependent information about a magnetic field distribution in a homogeneity volume including an examination volume of the MR system is provided when the movable patient support is located at a first position, wherein a stationary field map including information about a magnetic field distribution in the homogeneity volume is provided, which is independent of the position of the movable patient support, wherein a position dependent field map including information about a magnetic field distribution in the homogeneity volume mainly influenced by a position of the movable patient support is determined using the stationary field map and the first resulting field map, and wherein a second resulting field map in the homogeneity volume is determined when the movable patient support is located at a second position different from the first position, using the stationary field map and the position dependent field map.

Claims

1. A method for determining a field map in a magnetic resonance (MR) system comprising a movable patient support, the method comprising: providing a first resulting field map having position dependent information about a magnetic field distribution in a homogeneity volume comprising an examination volume of the MR system when the movable patient support is located at a first position; providing a stationary field map having information about a magnetic field distribution in the homogeneity volume, which is independent of the position of the movable patient support; determining a position dependent field map having information about a magnetic field distribution in the homogeneity volume influenced by a position of the movable patient support using the stationary field map and the first resulting field map; and determining a second resulting field map in the homogeneity volume when the movable patient support is located at a second position different from the first position, using the stationary field map and the position dependent field map.

2. The method of claim 1, wherein the first resulting field map is an absolute field map of a resulting magnetic field in the homogeneity volume as used for a MR measurement in the examination volume of the MR system.

3. The method of claim 2, wherein the second resulting field map is determined based on a displacement between the first and the second position of the movable patient support.

4. The method of claim 3, wherein the second resulting field map is determined using the position dependent field map, and wherein the position of the position dependent field map is shifted relative to the stationary field map by the displacement of the movable patient support.

5. The method of claim 1, wherein the determining of the position dependent field map comprises calculating a difference between the first resulting field map and the stationary field map.

6. The method of claim 1, wherein the second resulting field map is determined based on a displacement between the first and the second position of the movable patient support.

7. The method of claim 6, wherein the second resulting field map is determined using the position dependent field map, and wherein the position of the position dependent field map is shifted relative to the stationary field map by the displacement of the movable patient support.

8. The method of claim 7, wherein the second resulting field map is determined according to the relation: $B\left(x,y,z,\mathrm{SHIM},\mathrm{TP}2\right)=B_{\mathrm{DCS}}\left(x,y,z,{\mathrm{SHIM}}^{\mathrm{stat}}\right)+B_{\mathrm{table}}\left(x,y,z-z_{\mathrm{TP}1}+z_{\mathrm{TP}2},{\mathrm{SHIM}}^{\mathrm{move}},\mathrm{TP}1\right),$ wherein: B(x,y,z,SHIM,TP2) is the second resulting field map, B.sub.DCS(x,y,z,SHIM.sup.stat) is the stationary field map, B.sub.table (x,y,z−z.sub.TP1+z.sub.TP2,SHIM.sup.move,TP1) is the position dependent field map shifted by the displacement d=z.sub.TP2−z.sub.TP1, z.sub.TP2 corresponds to the z-coordinate of the second position of the movable patient support, and z.sub.TP1 corresponds to the z-coordinate of the first position of the movable patient support, and wherein an overall shim condition SHIM=(SHIM.sup.stat,SHIM.sup.move) comprises a contribution SHIM.sup.stat by stationary shim coils, and a contribution SHIM.sup.move by movable Coilshims, which are moved together with the patient support.

9. The method of claim 8, wherein the second resulting field map is only determined using the stationary field map and the position dependent field map, when the displacement is smaller than a movement threshold determined based on a following examination volume.

10. The method of claim 9, wherein the second resulting field map is measured using MR signals from the homogeneity volume when the displacement is larger than the movement threshold determined based on the following examination volume.

11. The method of claim 7, wherein the second resulting field map is only determined using the stationary field map and the position dependent field map, when the displacement is smaller than a movement threshold determined based on a following examination volume.

12. The method of claim 11, wherein the second resulting field map is measured using MR signals from the homogeneity volume when the displacement is larger than the movement threshold determined based on the following examination volume.

13. The method of claim 1, wherein the position dependent field map is only influenced by the position of the movable patient support and shim coils moved together with the patient support relative to stationary elements of the MR system.

14. The method of claim 1, wherein a resulting field map is provided for each position of a plurality of different positions of the movable patient support, and wherein a stationary field map comprising information about a magnetic field distribution in a homogeneity volume of the MR system, which is independent of the positions of the movable patient support, is provided, wherein an overall position dependent field map comprising information about a magnetic field distribution influenced by each position of the movable patient support is determined using the stationary field map and the plurality of resulting field maps, and wherein an intermediate resulting field map is determined while the movable patient support is located at an intermediate position between two positions of the movable patient support, using the stationary field map and the overall position dependent field map.

15. The method of claim 14, wherein the different positions of the movable patient support are adjacent to each other or overlapping each other.

16. The method of claim 15, wherein the method is performed using continuous movement of the movable patient support.

17. The method of claim 14, wherein the method is performed using continuous movement of the movable patient support.

18. A method for determining a change of a stationary magnetic field in a magnetic resonance (MR) system with a movable patient support, the method comprising: providing a resulting field map for each of a plurality of different positions of the movable patient support, wherein the resulting field map is based on a stationary magnetic field not influenced by position of the movable patient support and a position dependent magnetic field influenced by each position of the movable patient support; averaging the plurality of resulting field maps; and determining a change of the stationary magnetic field of the MR system based on the average of the plurality of resulting field maps.

19. A magnetic resonance (MR) system with a movable patient support for determining a magnetic field map, the MR system comprising: a memory configured to store program code; and a MR controller coupled with the memory and configured to execute the program code, wherein execution of the program code by the MR controller is configured to cause the MR system to: provide a first resulting field map having position dependent information about a magnetic field distribution in a homogeneity volume comprising an examination volume of the MR system when the movable patient support is located at a first position; provide a stationary field map having information about a magnetic field distribution in the homogeneity volume, which is independent of the position of the movable patient support; determine a position dependent field map having information about a magnetic field distribution in the homogeneity volume influenced by a position of the movable patient support using the stationary field map and the first resulting field map; and  determine a second resulting field map in the homogeneity volume when the movable patient support is located at a second position different from the first position, using the stationary field map and the position dependent field map.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present disclosure will now be described in more detail with reference to the accompanying drawings.

(2) FIG. 1 illustrates a schematic drawing of a MR system including a movable patient support with which a method for determining a field map may be carried out, according to certain embodiments.

(3) FIG. 2 illustrates a schematic drawing of another MR system including a movable patient support in a first and second position, according to certain embodiments.

(4) FIG. 3 illustrates a schematic drawing of the MR system of FIG. 2 with corresponding magnetic field maps, according to certain embodiments.

(5) FIG. 4 schematically illustrates a flow chart with acts for performing a method for determining a field map in an MR system with a movable patient support, according to certain embodiments.

(6) FIG. 5 schematically illustrates a flow chart with acts for performing a method for determining a change of a stationary magnetic field in a MR system with a movable patient support, according to certain embodiments.

DETAILED DESCRIPTION

(7) In the following, concepts in accordance with exemplary embodiments will be explained in more detail and with reference to the accompanying drawings.

(8) The drawings are to be regarded as being schematic representations and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to a person skilled in the art. Any connection or coupling between functional blocks, devices, components, modules, or other physical or functional units shown in the drawings or described herein may also be implemented by a direct or indirect connection or coupling. A coupling between components may also be established over a wireless connection. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof.

(9) FIG. 1 illustrates a schematic drawing of an MR system 1 including a movable patient support 2 with which a method for determining a field map may be carried out, according to certain embodiments.

(10) Referring to FIG. 1, an MR system 1 is described, with which, as explained below, a magnetic field map may be determined based on position of a patient support. An examination subject 12, or an examining object, is located in an examining tunnel of MR system 1. The MR system 1 includes a magnet 10 for generating a basic field B0, whereby an examination subject 12 is positioned on a patient support 2, (e.g., patient table), of the MR-system. Inside the magnet, a homogeneity volume 22 including an examination volume 21 is formed. The patient support 2 is moved in the center of the magnet 10 into the homogeneity volume 22 including an examination volume 21, such that the MR system receives spatially coded magnetic resonance signals from the examination volume 21. By irradiation of RF pulse sequences and switching of magnetic field gradients, the nuclear spins in the examination volume 21 may be deflected from the equilibrium position and currents induced by the magnetization generated by the base field B0 and the return to the equilibrium position may be converted into magnetic resonance signals in the receiving coils. The general mode of operation for the generation of MR images and the detection of the magnetic resonance signals are known to a person skilled in the art, so that a detailed explanation thereof is omitted in the following.

(11) The MR system 1 includes a MR controller 13, which is used for controlling the MR system 1. The central MR controller 13, which is configured to perform the method described below for determining a field map, further includes a gradient controller 14 for controlling and switching the magnetic field gradients, and a RF controller 15 for controlling and irradiating the RF pulses for deflecting the nuclear spins from the equilibrium position. In a memory unit 16, for example, the imaging sequences necessary for recording the MR images may be stored, as well as the programs which are necessary for the operation of the MR system 1. A recording unit 17 controls the image recording and thus controls the sequence of the magnetic field gradients and RF pulses and the reception intervals of MR signals as a function of the selected imaging sequences. The recording unit 17 also controls the gradient control 14 and the HF control 15. MR images, which may be displayed on a display 18, may be calculated in a computing unit 20, whereby an operator operates the MR system via an input unit 19. The memory 16 may have imaging sequences and program modules which carry out the method when executed in the computing unit 20 of one of the modules shown. The RF controller 15 may further be configured to improve the method for determining a magnetic field map, as is explained in the following in detail. In particular, memory 16 stores control information which may be derived from the MR controller 13. Further, the recording unit 17 is configured to perform the following method for determining a magnetic field map.

(12) The MR system of FIG. 1 is configured in such a way that, during the execution of the control information in the MR controller 13, a method for determining a field map is performed.

(13) FIG. 2 illustrates a schematic drawing of another MR system 1 including a movable patient support 2 in a first position 3 and a second position 4.

(14) The MR system 1 illustrated in FIG. 2 is designed similar to MR system 1 illustrated in FIG. 1, wherein MR system 1 includes a movable patient support 2, a magnet 10, a homogeneity volume 22, an examination volume 21, a memory 16 configured to store program code, and an MR controller 13 coupled with the memory 16 and configured to execute the program code. The patient support 2 may be located at different positions within MR system 1. For example, the patient support 2 may be located at a first position 3 within MR system 1, as shown in FIG. 2, or patient support 2 may be located at a second position 4 within MR system 1 differing from the first position 3 by a displacement d.

(15) The basic idea is the separation of B.sub.DCS(SHIM) and B.sub.table(TP). This is made possible by use of a so-called absolute field map, which may for example be based on the 3-echo method, as described, for example, in U.S. Patent Application Publication No. 2015/0204955 A1, or other methods as known in the art. A further prerequisite is the knowledge of B.sub.DCS(SHIM).

(16) This is the case because the significant contributions are known: The basic magnetic field is measured during installation of the MR system and the non-ideal components of the gradients and shims are also known. Thus, the table-fixed inhomogeneities may be calculated from the measured absolute field map and handled separately:
B.sub.table(x,y,z,TP1,SHIM.sup.move)=B(x,y,z,SHIM,TP1)−B.sub.DCS(x,y,z,SHIM.sup.stat)

(17) These two components B.sub.table(TP1,SHIM.sup.move) and B.sub.DCS(SHIM.sup.stat) are stored separately and used for further calculation of a field map at a different table position:
B(x,y,z,SHIM,TP2)=B.sub.DCS(x,y,z,SHIM.sup.stat)+B.sub.table(x,y,z,SHIM.sup.move,TP1,TP2)

(18) Assuming that the table only moves along the z-coordinate, the following relation applies to table positions TP1 at z.sub.TP1 and TP2 at z.sub.TP2:
B(x,y,z,SHIM,TP2)=B.sub.DCS(x,y,z,SHIM.sup.stat)+B.sub.table(x,y,z−z.sub.TP1+z.sub.TP2,SHIM.sup.move,TP1)

(19) The spatial extent of the magnetic field B.sub.table (TP) is limited to the spatial extent of the measured field map and thus to the homogeneity volume. A calculation of the field map over the total homogeneity volume is not possible. However, if the next diagnostic measurement at table position TP2 requires information about a region with limited extent along the z-direction only, then the information measured before may still be sufficient.

(20) As an example, in a first measurement, a field map is determined over a range in z-direction extending over 30 cm, e.g., the magnetic field is known over +/−15 cm. In a second measurement at table position TP2=TP1+10 cm, the field map may be determined in a range from −5 cm to +25 cm. For example, if the second measurement only covers a centered stack of layers with an extension of 10 cm, then no new field map may have to be measured.

(21) For strongly varying table positions, there is not enough information to calculate B(x,y,z,SHIM,TP2). A new measurement is therefore necessary in this case. If TP1 and TP2 do not differ by more than the extension of the field map measurement in z-direction minus a tolerance value, then B.sub.table(TP1,SHI.sup.move) and B.sub.table(TP2,SHIM.sup.move) complement each other to a correspondingly larger information, which is longer in z-direction. Then, a field map B(x,y,z,SHIM,TP3) may also be calculated directly at a table position TP3 between TP1 and TP2.

(22) FIG. 3 illustrates a schematic drawing of the MR system 1 of FIG. 2 with corresponding magnetic field maps.

(23) A first resulting field map 23 corresponds to a first position of the patient support 2 in MR system 1. After displacing the patient support 2 by displacement d, the patient support is disposed at a second position 4. Along with the patient support 2, the position dependent magnetic field map, which may be only dependent of elements moved together with the patient support 2, is also displaced by displacement d. The MR system 1, as illustrated in FIGS. 2 and 3, may therefore determine a second magnetic field, when the movable patient support 2 is located at a second position 4 different from the first position 3, using the stationary field map 24 and the position dependent field map 25. In particular, execution of the program code by the MR controller 13 may cause the MR system 1 to perform the method according to the following acts. In one act, a first resulting field map 23 including position dependent information about a magnetic field distribution in homogeneity volume 22 including examination volume 21 of the MR system 1 is provided when the movable patient support 2 with examination subject 12 is located at a first position 3. In a further act, a stationary field map 24 including information about a magnetic field distribution in homogeneity volume 22 is provided, which is independent of the position of the movable patient support 2. In particular, the stationary field map includes magnetic field components of the stationary shim coils, and therefore, even when the currents through the stationary field coils change, the changed stationary field map may be calculated using the changed currents through the stationary shim coils. Likewise, the position dependent field map 25 includes magnetic field components of the movable shim coils, (e.g., Coilshims), wherein when the currents through the movable shim coils change, the changed position dependent field map may be calculated using the changed currents through the movable shim coils. In another act, a position dependent field map 25 including information about a magnetic field distribution in homogeneity volume 22 mainly influenced by a position of the movable patient support 2 is determined using the stationary field map 24 and the first resulting field map 23. In a further act, a second resulting field map 26 in the homogeneity volume 22 is determined when the movable patient support 2 is located at a second position 4 different from the first position 3, using the stationary field map 24 and the position dependent field map 25. In one embodiment, the second resulting field map is determined in a volume, which is smaller than the homogeneity volume 22, e.g., as small as the intersection of stationary field map 24 and position dependent field map 25. In another embodiment, the above-described method may be performed for an arbitrary volume within MR system 1 other than the homogeneity volume 22, e.g., a second resulting field map may be determined for an arbitrary other volume than homogeneity volume, e.g., only the examination volume 21.

(24) FIG. 4 schematically illustrates a flow chart with acts for performing a method for determining a field map in an MR system 1 with a movable patient support 2.

(25) The method starts in act S10. In act S20, a first resulting field map 23 including position dependent information about a magnetic field distribution in a homogeneity volume 22 including an examination volume 21 of the MR system 1 is provided when the movable patient support 2 is located at a first position 3. In act S30, a stationary field map 24 including information about a magnetic field distribution in the homogeneity volume 22 is provided, which is independent of the position of the movable patient support 2 and includes magnetic field components generated by stationary shim coils, as described above. In act S40, a position dependent field map 25 including information about a magnetic field distribution in the homogeneity volume 22 mainly influenced by a position of the movable patient support 2 is determined using the stationary field map 24 and the first resulting field map 23. In act S50, a second resulting field map 26 in the homogeneity volume 22 is determined when the movable patient support 2 is located at a second position 4 different from the first position 3, using the stationary field map 24 and the position dependent field map 25. The method ends in act S90.

(26) The stationary contributions of the basic magnetic field may slightly change due to external influences, e.g., installation of another large device in the immediate neighborhood.

(27) If averaging is carried out over many measurements B(x,y,z,SHIM,TP), then the influences of non-stationary magnetic fields are averaged, leaving a measure for the actual scanner inhomogeneity. This may be carried out continuously and thus possible changes in the scanner inhomogeneity may be detected. With self-learning algorithms, small changes may, if necessary, be directly implemented as corrections. In the case of large changes, a new determination of the basic magnetic field may be triggered.

(28) FIG. 5 schematically illustrates a flow chart with acts for performing a method for determining a change of a stationary magnetic field 24 in a MR system 1 with a movable patient support 2.

(29) The method starts in act S10. In act S60, a resulting field map 23 is provided for each of a plurality of different positions of the movable patient support 2, wherein the resulting field map 23 is based on a stationary magnetic field 24 substantially not influenced by position of the movable patient support 2 and a position dependent magnetic field 25 mainly influenced by each position of the movable patient support 2. In act S70, the plurality of resulting field maps 23 is averaged, e.g., an average is calculated between a plurality of resulting magnetic field values for each voxel. In act S80, a change of the stationary magnetic field 24 of the MR system 1 is determined based on the average of the plurality of resulting field maps 23. The method ends in act S90.

(30) From the above, certain conclusions may be drawn:

(31) The first resulting field map may be an absolute field map of the resulting magnetic field in the homogeneity volume as used for a MR measurement in the examination volume of the MR system. It may be measured by a 3-echo-method as known in the art. By providing an absolute field map as described above, a resulting magnetic field in the homogeneity volume and corresponding shim settings may be determined more reliably and more precisely.

(32) Determining a position dependent field map may include calculating a difference between the first resulting field map and the stationary field map. Calculating a difference between the first resulting field map and the stationary field map provides efficient determination of position dependent magnetic field components in the homogeneity volume of the MR system.

(33) The second resulting field map may be determined based on a displacement between the first and the second position of the movable patient support. In some embodiments the displacement takes place substantially in the z-direction of the MR system, in other embodiments, (e.g., in open C-shaped MR systems), the displacement may take place two dimensions, wherein the method may be applied to any displacement. By using the displacement between the first and the second position of the movable patient support, the information about position dependent magnetic field components corresponding to the patient support and the examination subject on the patient support used to more reliably and efficiently determine a magnetic field map and corresponding shim settings based on displacement of the patient support.

(34) The second resulting field map may be determined using the position dependent field map, wherein the position of the position dependent field map is shifted relative to the stationary field map by the displacement of the movable patient support. Shifting the position of the position dependent field map according to the displacement of the movable patient support, allows to more reliably and efficiently determine a magnetic field map and corresponding shim settings based on displacement of the patient support.

(35) The second resulting field map may be determined according to the relation:
B(x,y,z,SHIM,TP2)=B.sub.DCS(x,y,z,SHIM.sup.stat)+B.sub.table(x,y,z−z.sub.TP1+z.sub.TP2,SHIM.sup.move,TP1),

(36) B(x,y,z,SHIM,TP2) is the second resulting field map; B.sub.DCS(x,y,z,SHIM) is the stationary field map; B.sub.table(x,y,z−z.sub.TP1+z.sub.TP2,SHIM.sup.move,TP1) is the position dependent field map (measured at TP1) shifted by the displacement d=z.sub.TP2−z.sub.TP1; z.sub.TP2 corresponds to the z-coordinate of the second position of the movable patient support; z.sub.TP1 corresponds to the z-coordinate of the first position of the movable patient support; and wherein the overall shim condition SHIM=(SHIM.sup.stat, SHIM.sup.move) including a contribution SHIM.sup.stat by stationary shim coils, and a contribution SHIM.sup.move by movable Coilshims, which are moved together with the patient support. The relation described above enables a fast and efficient calculation of a magnetic field map and corresponding shim settings based on displacement of the patient support.

(37) The position dependent field map may be substantially only influenced by the position of the movable patient support and components such as Coilshims, which are moved together with the patient support, relative to the stationary elements of the MR system. Therein, stationary magnetic field components based on stationary, non-movable elements in the MR-system, do not substantially influence the position dependent field map, and other magnetic field components which are based on elements movable with the patient support, such as Coilshims, the patient support itself and the patient mainly influence the position dependent field map. By considering mainly only magnetic field components dependent on position of the patient support, determination of a magnetic field map and corresponding shim settings based on displacement of the patient support may be performed more reliably and efficiently.

(38) A second resulting field map may be only determined using the stationary field map and the position dependent field map, when the displacement is smaller than a movement threshold determined based on a following examination volume. In another embodiment, the second resulting field map may only be determined, if the adjustment volume for the following examining volume is within the intersection volume of the stationary field map and the position dependent field map. In this case, the threshold may be determined based on the relation of the adjustment volume to the intersection volume.

(39) Using such a threshold provides more reliability and preciseness for the method, as positions of the patient support are excluded, where the patient support is moved as far to a position, where not enough information is available in the homogeneity volume to precisely determine a magnetic field map and corresponding shim settings.

(40) The second resulting field map may be measured using MR signals from the homogeneity volume when the displacement is larger than a movement threshold determined based on the following examination volume. In particular, in order to enable the calculation of the second resulting field map, the threshold is chosen as large as possible.

(41) For the so-called MDS adjustments, an isocentrically measured volume, which extends only a few centimeters in z-direction, is measured. According to the above-described method using absolute field maps, a plurality of N magnetic fields corresponding to different table positions B.sub.table(TP1,SHIM.sup.move) to B.sub.table(TPN,SHIM.sup.move) may be determined successively while the table moves from one table position to the next table position, (e.g., while the table moves continuously).

(42) The extensions and distances in z-direction of this plurality of measurements are selected in such a way that a seamless map of the lying inhomogeneities may be calculated from B.sub.table(TP1,SHIM.sup.move) to B.sub.table(TPN,SHIM.sup.move):B.sub.table(TP1−TPN,SHIM.sup.move). The map may correspond to the complete body of a patient, or partial regions of the body of the patient, which are of interest for MR imaging. Thus, with one MDS-Adjustment-Scan the field map B(x,y,z,SHIM,TP) may be determined for each table position, and a complete shim calculation is performed thereon.

(43) Accordingly, a resulting field map may be provided for each of a plurality of different positions of the movable patient support, a stationary field map including information about a magnetic field distribution in a homogeneity volume of the MR system, which is independent of the positions of the movable patient support may be provided, an overall position dependent field map including information about a magnetic field distribution mainly influenced by each position of the movable patient support may be determined using the stationary field map and the plurality of resulting field maps, and an intermediate resulting field map may be determined while the movable patient support is located at an intermediate position between two positions of the movable patient support, using the stationary field map and the overall position dependent field map. Using a plurality of position dependent field maps for a plurality of different patient support, which furthermore may be merged to an overall position dependent field map, enables determining accurate shim settings for all possible patient support positions lying between the measured patient support positions.

(44) The different positions of the movable patient support are adjacent to each other or overlapping each other, whereby only one reference scan may be sufficient for a plurality of measurements on an examining position, without the need of recurring reference scans to determine new shim settings when the patient support is moved to an arbitrary intermediate position.

(45) The method is performed using substantially continuous movement of the movable patient support, enabling a smooth transition for an examination subject and a more efficient method for determining new shim settings by only one reference scan.

(46) Summarizing, a method for determining a field map and corresponding shim settings in a MR system including a movable patient support is provided, wherein an absolute B0 field map is used and magnetic field inhomogeneities are first separated into stationary magnetic field components and table position dependent magnetic field components, in order to then add these components again to determine a magnetic field map based on a new desired table position. Effectively, a significantly larger value for the table movement threshold may be used resulting in a saving of adjustment time and thus gives the customer more time for imaging, which may be used to more precisely and effectively determine a magnetic field map and corresponding shim settings, perform additional diagnostic measurements, or achieve shorter examination times.

(47) It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

(48) While the present disclosure has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.