WO2015166267A1

WO2015166267A1 - Imaging techniques

Info

Publication number: WO2015166267A1
Application number: PCT/GB2015/051282
Authority: WO
Inventors: Frederic Festy; Richard Cook; Timothy Watson
Original assignee: King's College London
Priority date: 2014-05-02
Filing date: 2015-05-01
Publication date: 2015-11-05
Also published as: GB201407787D0

Abstract

Aspects and embodiments provide a method of collecting a dataset representative of a specimen and an apparatus operable to perform the method. The method and apparatus use an optical sensor array configured to detect received electromagnetic radiation in a first optical channel and a second optical channel, an overlap region of optical electromagnetic radiation lying within both the first and second optical channels. The method comprises: selecting at least two discrete optical illumination bands of electromagnetic radiation such that after interaction with the specimen, the discrete optical illumination bands each lie within one of the first and second optical channel and outside the overlap region; illuminating the specimen with the at least two optical illumination bands; and collecting the at least two optical illumination bands after interaction with the specimen using the optical sensor array to form a dataset representative of the specimen. Such a method and apparatus recognises that filters used to chromatically and optically separate channels, for example, a red, green or blue channel are typically tuned to the response spectra of an image reproduction device to be viewed by a human eye. Such response spectra are often such that the channels substantially overlap, which can enhance a resulting image visually but may make any quantitative analysis of an optical imaging dataset representative of an object misleading. By tuning the illumination spectrum in accordance with the sensing device, it is possible to obtain useful quantitative results from standard imagine devices.

Description

IMAGING TECHNIQUES

FIELD OF THE INVENTION

The present invention relates to a method of collecting a dataset representative of a specimen using an optical sensor array and apparatus operable to collect a dataset representative of a specimen.

BACKGROUND

Optical imaging technologies are known. Typical imaging apparatus comprises an electromagnetic radiation sensor, often a CCD or CMOS, which is arranged to detect electromagnetic radiation in the optical region and convert that detected

electromagnetic radiation into one or more electronic signals. Those electronic signals can be used to create an image to be read by a human eye, for example, by means of a photograph, or an electronic screen comprising an image reproduction array.

According to one typical optical imaging arrangement, a CCD array is arranged in combination with a Bayer mask. An example Bayer mask is illustrated schematically in Figure 1. Such a mask may comprise a red-green-green-blue (RGGB) filter

configuration. The filter is arranged such that each element of the CCD array is associated with a 2x2 RGGB filter arrangement. Two green filters are provided for each red and blue filter since the human eye is more sensitive to green than red or blue. The optical filters are operable to transmit optical radiation having wavelengths in the red, green or blue region of the spectrum respectively. The information collected by elements of the CCD array and Bayer mask combination can then be reproduced by an appropriate arrangement of RGB transmission elements, for example, those in an LCD display, to form an image readable by the human eye.

Filters used in relation to optical sensor arrays are typically tuned to closely match the optical response and sensing characteristics of the physiology of a human eye. Figure 2 illustrates schematically spectral sensitivity to colour of a human eye. Figure 3 illustrates schematically spectral sensitivity of an example CCD array and Bayer mask combination.

According to an alternative typical optical imaging arrangement, a 3-CCD device (a single capture device with three separate array sensors) is provided, such that each channel (RGB) can be measured separately. That is to say, each of the CCDs is tuned to respond to a particular colour. Pixel to pixel (CCD array element to array element) mapping can be implemented in relation to the 3 CCDs such that an appropriate data set can be formed allowing production of an image of an object. The operation of such a 3 CCD sensing arrangement is also typically matched to the optical response and sensing characteristics of a human eye.

In particular, the colour response of each of the sensing CCDs is matched to the spectral response of conventional means of display which, in turn, follow the spectral response of a human eye. Although optical sensing arrangements are known, they may not suit all data capture applications. Accordingly, it is desired to provide an alternative optical sensing arrangement.

SUMMARY

A first aspect provides a method of collecting a dataset representative of a specimen using an optical sensor array configured to detect received electromagnetic radiation in a first optical channel and a second optical channel, an overlap region of optical electromagnetic radiation laying within both the first and second optical channels; the method comprising: selecting at least two discrete optical illumination bands of electromagnetic radiation such that after interaction with the specimen, the discrete optical illumination bands each lie within one of the first and second optical channel and outside the overlap region ; illuminating the specimen with the at least two optical illumination bands; and collecting the at least two optical illumination bands after interaction with the specimen using the optical sensor array to form a dataset representative of the specimen.

In other words, the first aspect provides a method of collecting a dataset representative of a specimen using an optical sensor array configured to detect received photons in a first optical detection spectrum and a second optical detection spectrum, wherein there is a detection bleed through region of photon energies which lie within both the first and second optical detection spectra; the method comprising: selecting at least two discrete optical illumination bands of photon energies such that after interaction with the specimen, the discrete optical illumination bands each lie within one of the first and second optical detection spectra and outside the bleed through region ; illuminating the specimen with the at least two optical illumination bands; and collecting the at least two optical illumination bands after interaction with the specimen using the optical sensor array to form a dataset representative of the specimen. The first aspect recognises that filters used to chromatically and optically separate channels, for example, a red, green or blue channel are typically tuned to the response spectra of an image reproduction device to be viewed by a human eye. Such response spectra are often such that the channels substantially overlap, which can enhance a resulting image visually but may make any quantitative analysis of an optical imaging dataset representative of an object misleading due to optical bleedthrough of one detection channel into one or more other detection channels. That is to say, there is overlap of the transmission spectra of filters used to define each channel. By tuning the illumination spectrum in accordance with a chosen sensing device, it is possible to obtain useful quantitative results from standard optical detection devices. The first aspect recognises that the useful detection signal associated with a detection channel may be corrupted by a detection signal in one or more other channels. The first aspect essentially increases signal to noise ratio in a captured dataset by removing corrupting signal from other detection channels.

The first aspect recognises that typical detector arrangements may operate such that a captured dataset representative of an image is likely to have a large degree of contamination between detection channels. Such datasets allow recordal and subsequent reproduction of an image which is likely to be pleasing to the human eye since often the response of detection channels of a detector are selected to mimic the response of the human eye. Although such a dataset may produce visually pleasing images, meaningful numerical analysis of the dataset may be hampered by such cross channel contamination. It is, in some known arrangements, possible to deconvolute a dataset in which channel contamination has occurred, but such deconvolution may be time consuming and/ or computationally complex.

Some embodiments of the first aspect may recognise that, in an extreme case, in order to ensure a "clean" dataset from a detector, overlap between detection channels may be no greater than the level of noise typically recorded in a detection channel. In some embodiments, the overlap between adjacent detection channels in terms of collected photons in one detection channel which may also fall into an adjacent detection channel and thus be recorded by both, for example, may be less than l.o percent. In some embodiments, the overlap may be less than 0.1 percent.

It will be appreciated that the amount of overlap, or contamination, of one detection channel into another, might be considered to be the proportion of unwanted photons from one "unwanted" detection channel which are also recorded in a detection channel of interest. For example, if X photons are detected in a blue detection channel but 10 % of those detected photon are also recorded in the green channel, there is a photon contamination in number of 0.1 times X. For a source which provides as many green photons as blue photons, then the overlap can be obtained by looking at the overlap of areas under the detection channel sensitivity curves.

It will, of course, be appreciated that in some cases, an overlap minimum could be considered to occur when the number of unwanted photons reaches the detection limit of the detector in a wanted channel, which may be detector dependent, since it depends upon the electronic and detection surface of the detector. Another overlap minimum may be considered to occur when the number of unwanted photon reach the poisson noise of the wanted photon, (or the square root of it). The maximum overlap limit may be determined by an intended dataset/ detector application. In some cases, the relationship between channel overlap is determined by a desired analysis error. In such scenarios, the upper overlap limit between adjacent channels may be set by what is tolerable in the results of subsequent dataset analysis. However, the overlap between two adjacent detection channels may, in some embodiments, be in the region of less than 10 times the average noise level of the detection channel of interest. In some arrangements, the maximum overlap may be in the region of 5 times the noise level and, in some embodiments, the maximum overlap may be in the region of 2 times the average noise level in the detection channel of interest.

It will be appreciated that an alternative means to achieve a similar result is the provision of a Bayer mask in which the RGB filters do not result in spectral detection bands which include overlap. That is to say where each of the RBG bands is distinct. However, manufacture of such a specialist device is not economically viable and such an arrangement may not imitate the operation of the human eye, so resulting images could be 1 less suited to viewing with the human eye and the total light captured by a sensing device is likely to be significantly reduced, leading to capture of a potentially poorer dataset in relation to a specimen. A method according to the first aspect may allow standard off-the-shelf imaging components to be used effectively for quantitative specimen analysis. The method of the first aspect may comprise collecting a dataset representative of a specimen. That dataset may comprise: a numerical dataset, a digital image created from the numerical dataset; an image or similar. The method may relate to imaging the specimen using an optical sensor array configured to detect received electromagnetic radiation in a first optical channel and a second optical channel, an overlap region of optical electromagnetic radiation laying within both the first and second optical channels. Accordingly, it will be understood that the optical sensor array may be configured to collect or sense electromagnetic radiation, in the optical part of the spectrum and record how much radiation is sensed in each of the "separate" channels. The first and second channels in accordance with the first aspect may include a region of partial overlap. That is to say, the first channel does not lie totally within the second channel or vice versa. There is a portion of the spectrum of the first channel which lies within a portion of the spectrum of the second channel. The first channel includes at least a portion of spectrum which lies inside a region of spectrum belonging to a second channel. Each of the channels may be characterised by a response curve according to radiation frequency or wavelength. The detection channels may be considered not to overlap if there is substantially no detection bleed through or crossover. Mathematically the overlap in a first channel between a first and second channel is defined as the integral of the spectra of each of the two channels, divided by the integral of the spectrum of the first channel squared. Two channels may be considered not to overlap if their mathematical overlap is calculated to be less than 10 % or more preferably, less than 1%. That is to say, there is considered to be no overlap if less than 10 % of a channel is common to another channel.

The optical sensor array may be configured to detect received electromagnetic radiation in a first optical channel and a second optical channel. The optical sensor array may be configured to detect received electromagnetic radiation in more than two channels. Each channel may correspond to a particular range of wavelengths or frequencies associated with a particular colour. The channels may, for example, comprise two or more of: a red, green and blue channel. The optical sensor array may be configured to detect in three channels. Adjacent channels may overlap. The optical sensor array may comprise one or more charge coupled devices (CCDs).

The method may comprise: selecting at least two discrete optical illumination bands of electromagnetic radiation such that after interaction with the specimen, the discrete optical illumination bands each lie within one of the first and second optical channel and outside the overlap region. Selection may comprise: selection of more than two discrete optical illumination bands with which to illuminate a specimen. Each illumination band may, after interaction with the specimen, lie within a different detection channel. Each detected illumination band may lie within a non-overlapping region of one of the detection channels.

Interaction with the specimen may comprise: reflection by the specimen, transmission by the specimen, or absorption by the specimen.

The method may comprise: illuminating the specimen with the at least two optical illumination bands; and collecting, sensing and/ or detecting the at least two optical illumination bands after interaction with the specimen using the optical sensor array. The information collected by the optical sensor forms a dataset representative of the specimen.

The dataset representative of the specimen may be recorded, stored, exported in a numerical format, shown on a display or similar. The dataset representative of the specimen may be used to perform a quantitative comparative analysis of the specimen in relation to the information collected by the optical sensor in the two detection channels.

In one embodiment, at least one of the discrete optical illumination bands is selected such that, after interaction with the specimen, the at least one discrete optical illumination band is substantially centred in the region of a detection response peak of one of the first or second optical channels. Selection of illumination bands in this way can help to ensure that enough light is collected by the optical sensor to form a meaningful dataset. It will be appreciated that use of a common broadband white light source, which is subsequently processed appropriately to provide the discrete optical illumination bands, may limit available overall illumination power, and that an arrangement which aligns illumination bands with detection response peaks may be particularly suitable. Selecting illumination to maximise collection in relation to a detection response curve can assist in obtaining a clear image of the specimen, even when overall illumination intensity from a white light source may be restricted. In particular, such selection may assist in obtaining a dataset or image with a strong signal to noise ratio. In one embodiment, at least one of the discrete optical illumination bands is selected to comprise a band having a width in the region of 50nm. In some embodiments, each discrete optical illumination band is selected in dependence upon the response profile of the optical sensor in each optical detection channel. In some embodiments, the optical illumination bands are selected such that, after interaction with the specimen, the optical illumination band lies wholly within a non-overlapping portion of the response profile of one or other of the first or second optical detection channel. Given typical optical sensor response profiles, avoiding detection in more than one optical channel may be achieved if electromagnetic radiation having a bandwidth of, for example, less than lOOnm is selected. In some embodiments, an illumination band having a bandwidth of less than 50nm is selected. It will be appreciated that when selecting bandwidth of an appropriate illumination band, it is necessary to consider both restriction of the band to a non-overlapping portion of a detection response curve, and total light collected in order to obtain a dataset representative of a specimen.

Restriction of an illumination band to a small range of wavelengths can help to ensure a clean image or potentially more meaningful dataset.

In one embodiment, illuminating the specimen with the at least two optical

illumination bands comprises: concurrently illuminating the specimen with the at least two optical illumination bands. Accordingly, such concurrent illumination with said first and second illumination bands allows for concurrent collection of data relating to a specimen, thus allowing a dataset to be collected in relation to moving or changing specimen so that data collected by each illumination band can be correlated to a specimen in both time and space.

In one embodiment, the method comprises: providing a white light illumination source and filtering the illumination source to illuminate the specimen with the at least two optical illumination bands. Accordingly, use of a broadband illumination spectrum is possible, together with appropriate beam splitters and use of filters to provide illumination bands having an appropriate bandwidth, selected in accordance with the properties of the optical sensor.

In one embodiment, the method comprises: independently controlling intensity of the at least two optical illumination bands. Accordingly, even though a single illumination source can be used it is possible to insert appropriate intensity modulation devices to control the intensity of each of the optical illumination bands independently.

Independent control of, for example, the red, green and blue bands of illumination can be used to improve resulting clarity of a dataset or image being obtained from an optical sensor. Such independent illumination control may be particularly useful when a single CCD sensor is used. For example, imaging of biological samples may suffer from saturation in the red, and thus the ability to modulate the intensity of a red illumination band may allow for collection of more meaningful data from blue and green illumination bands.

In one embodiment, the method comprises: comparing data collected by the optical sensor array in the first and second optical channels. Accordingly, meaningful quantitative analysis of the specimen may be obtained from the data collected by the optical sensor. The comparison may comprise comparing, or performing calculations in relation to data collected by the optical sensor in each of said overlapping spectral optical channels. In one embodiment, the optical sensor array comprises at least one CCD sensor array. That CCD sensor array may comprise a monochrome CCD sensor array in which a plurality of sensor elements are provided, in combination with an appropriate Bayer mask. The sensor elements in combination with the Bayer mask are typically operable to receive/ detect light in three (RGB) overlapping bands. Those RGB bands have been selected in accordance with operation of the human eye in order to aid visual reproduction of a specimen by video or picture. Selection of an appropriate

illumination spectrum aids scientific analysis of data collected by a standard CCD array. In some embodiments, the optical sensor may comprise a plurality of CCD arrays, configured such that each point on the specimen is "matched" across the plurality of CCD arrays. That is to say, more than one CCD array can be provided with points on a specimen mapped to equivalent elements on the multiple CCD arrays. Each CCD may be operable to receive or detect light in one or more of said optical channels.

In one embodiment, each element of the CCD sensor array is configured to detect received electromagnetic radiation in the first optical channel and the second optical channel, an overlap region of optical electromagnetic radiation lying within both the first and second optical channels. In one embodiment, the first and second optical channel comprise: at least two of: a red, green or blue optical channel. In some embodiments, an optical sensor may be operable to detect in alternative imaging regimes, for example, Cyan, Magenta, Yellow rather than Red, Green, Blue. In one embodiment, the method comprises: a method of imaging biological specimen. Accordingly, use of a restricted illumination spectrum may allow biological tissue to be effectively imaged using less energy, with the result that heating effects and heat damage of tissue can be mitigated, whilst still obtaining a clear image of a specimen.

It will, for example, be appreciated, that an alternative arrangement may allow for filtering of white light into narrower bands to allow for optimised detection according to the response profile of the optical sensor, that filtering occurring after interaction with the specimen, but before detection by the optical sensor. Such an arrangement still illuminates a biological sample with the full white light spectrum and may result in undesirable heating of the specimen. That heating may cause changes to the specimen, such that observation itself changes the experimental results.

A second aspect provides apparatus operable to collect a dataset representative of a specimen, the apparatus comprising: an optical sensor array configured to detect received electromagnetic radiation in a first optical channel and a second optical channel, an overlap region of optical electromagnetic radiation laying within both the first and second optical channels; an illumination source operable to illuminate the specimen with at least two optical illumination bands, the at least two discrete optical illumination bands of electromagnetic radiation being selected such that after interaction with the specimen, the discrete optical illumination bands each lie within one of the overlapping optical channels and outside the overlap region ; and a data collection device operable to collect the at least two optical illumination bands after interaction with the specimen from the optical sensor array to form a dataset representative of the specimen.

In one embodiment, at least one of the discrete optical illumination bands is selected such that, after interaction with the specimen, the at least one discrete optical illumination band is substantially centred in the region of a detection response peak of one of the first or second optical channels.

In one embodiment, at least one of the discrete optical illumination bands is selected to comprise a band having a width of 50nm or less. In one embodiment, the illumination source is arranged to concurrently illuminate the specimen with the at least two optical illumination bands. In one embodiment, the illumination source comprises: a white light illumination source arranged to be filtered before illumination of the specimen to provide the at least two optical illumination bands. In one embodiment, the apparatus comprises: an illumination band intensity control device operable to independently control intensity of each of the at least two optical illumination bands.

In one embodiment, the apparatus comprises: comparison logic operable to compare data collected by the optical sensor array in the first and second optical channels

In one embodiment, the optical sensor array comprises: at least one CCD sensor array.

In one embodiment, each element of the CCD sensor array is configured to detect received electromagnetic radiation in the first optical channel and the second optical channel, an overlap region of optical electromagnetic radiation lying within both the first and second optical channels.

In one embodiment, the first and second optical channel comprise: at least two of: a red, green or blue optical channel.

In one embodiment, the apparatus comprises: a biological specimen imaging apparatus. Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims. Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which :

Figure 1 illustrates schematically an example Bayer mask; Figure 2 illustrates schematically spectral sensitivity to colour of a human eye;

Figure 3 illustrates schematically spectral sensitivity of an example CCD array and Bayer mask combination ;

Figure 4 illustrates schematically apparatus according to one arrangement; and Figure 5 illustrates one example illumination spectrum together with a detection response profile according to one arrangement.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided.

Figure 4 illustrates schematically apparatus according to one arrangement. The apparatus shown comprises generally a light source 10 , a specimen 50 and an optical sensor array 70. The optical sensor array 70 shown in Figure 4 is configured to detect received electromagnetic radiation in three optical channels, according to an RGB detection response profile. An example of such a profile is shown in Figure 3. Those RGB detection channels overlap. As can be seen, adjacent optical channels have an overlap region of optical electromagnetic radiation which lay within both of the immediately adjacent optical channels.

The illumination source 10 of the arrangement shown comprises a white light source, which is passed through a beam splitter 30. Each sub-beam, in this case, 3 sub-beams, is then filtered by filters 40 , before illuminating the specimen 50. The filters are selected so that each of the three discrete optical illumination bands of electromagnetic radiation which illuminate the specimen are reflected 60 by the specimen and then lie within one of the optical detection channels of sensor array 70 but outside the channel overlap region.

The optical sensor array 70 comprises a CCD which is coupled to an appropriate data collection device 80 to form a dataset representative of the specimen. That dataset may be stored in digital form, or reproduced on a visual device 90 , for example, a PC screen or similar.

Figure 5 illustrates one example illumination spectrum together with a detection response profile according to one arrangement. The graph shown in Figure 5 shows that the illumination spectrum was split into three discrete bands, each of

approximately 50nm in width, the centre of each discrete band of illumination having been selected to lie in the region of the peak of one of the blue, red or green channel response curve.

In the arrangement illustrated, the illumination light was filtered into three narrow spectral bands corresponding to the position of the three peaks in spectral response of the CCD chosen as an optical sensor. Each illumination band is selected to be narrow enough for example, less than 50nm to avoid potential overlap with an adjacent illumination band. In the arrangement shown, the narrow blue band (460nm) was mainly detected in the blue channel; the green band (560nm) was detected in the green channel and the red band (650nm) in the red channel. In relation to biological samples, it has been found that such an illumination spectrum reduces illumination light from a Xenon source to approximately 10 % of the original illumination, yet does not have a degrading effect upon image quality. If used in, for example, an endoscope arrangement, such a reduction may mean that the temperature at the end of an endoscope probe is no longer above that of skin, or human tissue and thus results collected may be more representative, whilst also resulting in greater patient comfort.

It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. The description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions.

Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.

Claims

1. A method of collecting a dataset representative of a specimen using an optical sensor array configured to detect received electromagnetic radiation in a first optical channel and a second optical channel, an overlap region of optical electromagnetic radiation laying within both said first and second optical channels; said method comprising:

selecting at least two discrete optical illumination bands of electromagnetic radiation such that after interaction with said specimen, said discrete optical illumination bands each lie within one of said overlapping optical channels and outside said overlap region ;

illuminating said specimen with said at least two optical illumination bands; and collecting said at least two optical illumination bands after interaction with said specimen using said optical sensor array to form a dataset representative of said specimen.

2. A method according to claim 1, wherein at least one of said discrete optical illumination bands is selected such that, after interaction with said specimen, said at least one discrete optical illumination band is substantially centred in the region of a detection response peak of one of said first or second optical channels.

3. A method according to claim 1 or claim 2, wherein at least one of said discrete optical illumination bands is selected to comprise a band with a width of 50nm or less.

4. A method according to any preceding claim, in which illuminating said specimen with said at least two optical illumination bands comprises: concurrently illuminating said specimen with said at least two optical illumination bands.

5. A method according to any preceding claim, comprising: providing a white light illumination source and filtering said illumination source to illuminate said specimen with said at least two optical illumination bands.

6. A method according to any preceding claim, comprising: independently controlling intensity of said at least two optical illumination bands.

7. A method according to any preceding claim, comprising: comparing data collected by said optical sensor array in said first or second optical channels.

8. A method according to any preceding claim, wherein said optical sensor array comprises at least one CCD sensor array.

9. A method according to claim 8 , wherein each element of said CCD sensor array is configured to detect received electromagnetic radiation in said first optical channel and said second optical channel, an overlap region of optical electromagnetic radiation laying within both said first and second optical channels.

10. A method according to any preceding claim, wherein said first and second optical channel comprise: at least two of: a red, green or blue optical channel.

11. A method according to any preceding claim, comprising: a method of imaging biological specimen .

12. Apparatus operable to collect a dataset representative of a specimen, said apparatus comprising:

an optical sensor array configured to detect received electromagnetic radiation in a first optical channel and a second optical channel, an overlap region of optical

electromagnetic radiation laying within both said first and second optical channels; an illumination source operable to illuminate said specimen with at least two optical illumination bands, said at least two discrete optical illumination bands of

electromagnetic radiation being selected such that after interaction with said specimen, said discrete optical illumination bands each lie within one of said overlapping optical channels and outside said overlap region ; and

a data collection device operable to collect said at least two optical illumination bands after interaction with said specimen from said optical sensor array to form a dataset representative of said specimen.

13. A method or apparatus as substantially described herein with reference to the accompanying drawings.