Method and system for capturing images of a liquid sample
A method and system for capturing images of a liquid sample flowing through a field of view of an imaging device that can include stepping a focus mechanism of the imaging device through a plurality of focus values and capturing a plurality of images of the sample at each of the plurality of focus values as the sample flows through the field of view of the imaging device. In this way, image capture can proceed before a focus value has been determined and capture images that are in focus can be used for further processing subsequently.
1. A system for analysing a liquid sample flowing through a field of view of an imaging device, the system comprising:
an imaging device for imaging a liquid sample flowing through a field of view of the imaging device, the system configured to accept a microfluidic cartridge such that a channel on the microfluidic cartridge through which, in use the liquid sample flows is disposed relative to the field of view, wherein the imaging device has a focus mechanism for positioning at least a portion of the imaging device in accordance with a focus value; and
a processor configured to:
step a focus mechanism of the imaging device through a first plurality of focus values;
capture a plurality of images of the sample during flow at each of the first plurality of focus values as the sample flows through a field of view of the imaging device;
determine a focus measure for each of the plurality of captured images; and
identify for further processing a subset of the captured images based on the determined focus measures.
2. The system of claim 1 wherein stepping the focus mechanism through the plurality of focus values comprises repeatedly varying the focus value between a minimum value and a maximum value.
3. The system of claim 1 , wherein identifying a subset of the captured images comprises evaluating a criterion on the focus measure for each captured image and identifying for further processing images with a focus measure which meets the criterion.
4. The system of claim 1 , wherein the processor is configured to:
identify a first focus value based on the focus measures;
set the focusing mechanism of the imaging device to the first focus value; and
capture further images at the first focus value.
5. The system of claim 4 , wherein the processor is configured to identify for further processing images captured when the focusing mechanism was set to the first focus value.
6. The system of claim 4 , wherein the processor is configured to:
(a) step the focus mechanism of the imaging device through a second plurality of focus values;
(b) capture a plurality of images of the sample at each of the second plurality of focus values as the sample flows through the field of view of the imaging device;
(c) determine a focus measure for each of the images captured at each of the second plurality of focus values;
(d) identify a second focus value based on the focus measures determined in step (c);
(e) set the focusing mechanism of the imaging device to the second focus value; and
(f) capture further images at the second focus value.
7. The system of claim 6 , wherein the processor is configured to identify for further processing images captured when the focusing mechanism was set to the second focus value.
8. The system of claim 1 , wherein the processor is configured to:
determine a focus value based on the determined focus measures;
set a second plurality of focus values based on the determined focus value;
step a focus mechanism of the imaging device through the second plurality of focus values; and
capture a plurality of images of the sample at each of the second plurality of focus values as the sample flows through a field of view of the imaging device.
9. The system of claim 1 , wherein the processor is configured to further process the images in the subset.
10. The system of claim 9 , wherein further processing the images comprises determining a characteristic of the liquid sample or a component of the liquid sample based on the images in the subset.