It is important to regularly assess the quality and performance of a given microscope. This blog post will gather and describe a practical guide to microscopes quality control.
Illumination power warmup kinetic
When starting an instrument, it takes time to reach a stable steady state. This duration is known as the warmup period. It is critical to record a warmup kinetic at least once to accurately define this period.
Acquisition protocol
- Setup the Power Meter
- Place a power meter sensor (e.g., Thorlabs S170C) on the stage.
- Center the sensor under the objective.
- Prepare the Measurement
- Select the wavelength of the light source you wish to monitor using your power meter controller (e.g., Thorlabs PM400) or software.
- Zero the sensor to ensure accurate readings.
- Record the Warmup Kinetic
- Turn on the light source and immediately record the power output over time until it stabilizes.
- Repeat for Multiple Light Sources
- Repeat steps 2 to 3 for each light source you wish to monitor.
Results
For each light source plot the measured power output (mW) over time.
For this instrument the warmup time is virtually null.
Calculate the relative power: Relative Power = Power/MaxPower and plot the Relative Power (%) over time.
The 385nm, 475nm, and 630nm light sources exhibit some variability; however, this is unlikely to impact the measurement.
Conclusion
The warmup time for this specific instrument is virtually null but a 10 minutes warmup period is recommended.
Maximum illumination power output
This measure evaluates the maximum power output of each light source, considering both the quality of the light source and the components along the light path. Over time, we anticipate a gradual decrease in power output, accounting for the aging of the hardware, including the light source and other optical components.
Acquisition protocol
- Warm up the system
- Setup the Power Meter
- Place a power meter sensor (e.g., Thorlabs S170C) on the stage.
- Center the sensor under a low magnification objective.
- Prepare the Measurement
- Select the wavelength of the light source you wish to monitor using your power meter controller (e.g., Thorlabs PM400) or software.
- Zero the sensor to ensure accurate readings.
- Record the maximum illumination power output
- Turn on the light source to 100%
- Record the average power output.
- Repeat for Multiple Light Sources
- Repeat steps 3 to 4 for each light source you wish to measure.
Results
For each light source plot the measured maximal power output (mW) and compare it to the specifications from the manufacturer. Calculate the relative power: Relative Power = Measured Power / Specifications. The excel file provide a template that can be filled in Maximum Illumination Power Output_Template.xlsx
Conclusion
This instrument provides 80% of the power given by the manufacturer specifications. These results are consistent because the manufacturer specifications are using a different objective and likely different dichroic mirrors.
Illumination stability
The light sources used on a microscope should be constant or at least stable over the time scale of an experiment. For this reason power stability is recorded over 4 different time-scale.
This measure compares the power output over time. Four different timescales are measured:
- Real-time illumination stability: Continuous recording for 1 min
- Short-term illumination stability: Every 1-10 seconds for 5-15 min. This represents the duration of a z-stack acquisition
- Mid-term illumination stability: Every 10-30 seconds for 1-2 hours. This represent the duration of a typical acquisition session or short time-lapse experiments. For longer time-lapse experiments, longer duration may be used.
- Long-term illumination stability: Once a year or more over the lifetime of the instrument (this is measured in the Maximum Power Output section comparing with previous measurements)
The Stability factor is then calculated S (%) = 100 x (1- (Pmax-Pmin)/(Pmax+Pmin)).
The excel file provides a template that can be filled in Illumination Stability_Template.xlsx
Real-time illumination stability
Acquisition Protocol
- Warm up the system
- Setup the Power Meter
- Place a power meter sensor (e.g., Thorlabs S170C) on the stage.
- Center the sensor under a low magnification objective.
- Prepare the Measurement
- Select the wavelength of the light source you wish to monitor using your power meter controller (e.g., Thorlabs PM400) or software.
- Zero the sensor to ensure accurate readings.
- Record the maximum illumination power output
- Turn on the light source to 100%
- Record the power output as fast as possible for 1 minute
- Repeat for Multiple Light Sources
- Repeat steps 3 to 4 for each light source you wish to measure.
Results
For each light source plot the measured power output (mW) over time.
Calculate the relative power: Relative Power = Power/MaxPower and plot the Relative Power (%) over time.
Calculate the Stability factor S (%) = 100 x (1- (Pmax-Pmin)/(Pmax+Pmin)).
Stability Factor real-time | |
385nm | 99.98% |
475nm | 99.96% |
555nm | 99.95% |
630nm | 99.94% |
Conclusion
The light sources are highly stable (>99.9%) during a 1 min period.
Short-term illumination stability
Acquisition Protocol
- Warm up the system
- Setup the Power Meter
- Place a power meter sensor (e.g., Thorlabs S170C) on the stage.
- Center the sensor under a low magnification objective.
- Prepare the Measurement
- Select the wavelength of the light source you wish to monitor using your power meter controller (e.g., Thorlabs PM400) or software.
- Zero the sensor to ensure accurate readings.
- Record the maximum illumination power output
- Turn on the light source to 100%
- Record the power output every 10 seconds for 15 minutes
- Repeat for Multiple Light Sources
- Repeat steps 3 to 4 for each light source you wish to measure.
Results
For each light source plot the measured power output (mW) over time.
Calculate the relative power: Relative Power = Power/MaxPower and plot the Relative Power (%) over time.
Calculate the Stability factor S (%) = 100 x (1- (Pmax-Pmin)/(Pmax+Pmin)).
Stability Factor short-term | |
385nm | 99.72% |
475nm | 99.89% |
555nm | 99.99% |
630nm | 99.95% |
Conclusion
The light sources are highly stable (>99.7%) during a 15 min period.
Mid-term illumination stability
Acquisition Protocol
- Warm up the system
- Setup the Power Meter
- Place a power meter sensor (e.g., Thorlabs S170C) on the stage.
- Center the sensor under a low magnification objective.
- Prepare the Measurement
- Select the wavelength of the light source you wish to monitor using your power meter controller (e.g., Thorlabs PM400) or software.
- Zero the sensor to ensure accurate readings.
- Record the maximum illumination power output
- Turn on the light source to 100%
- Record the power output every 10 seconds for 1 h
- Repeat for Multiple Light Sources
- Repeat steps 3 to 4 for each light source you wish to measure.
Results
For each light source plot the measured power output (mW) over time.
Calculate the relative power: Relative Power = Power/MaxPower and plot the Relative Power (%) over time.
Calculate the Stability factor S (%) = 100 x (1- (Pmax-Pmin)/(Pmax+Pmin)).
Stability Factor mid-term | |
385nm | 99.63% |
475nm | 99.98% |
555nm | 99.97% |
630nm | To be acquired |
Conclusion
The light sources are highly stable (>99.5%) during a 1 h period.
Long-term illumination stability
Long-term illumination stability is intented to measure the power output over the lifetime of the instrument. This is measured in the Maximum Power Output section by comparing with previous measurements.
Illumination stability conclusion
Real-time 1 min | Short-term 15 min | Mid-term 1 h | |
385nm | 99.98% | 99.72% | 99.63% |
475nm | 99.96% | 99.89% | 99.98% |
555nm | 99.95% | 99.99% | 99.97% |
630nm | 99.94% | 99.95% | To be acquired |
The light sources are highly stable (>99.5%).
Illumination Input-Output Linearity
This measure compares the power output when the input varies. We expect a linear relationship between the input and the power output.
Acquisition Protocol
- Warm up the system
- Setup the Power Meter
- Place a power meter sensor (e.g., Thorlabs S170C) on the stage.
- Center the sensor under a low magnification objective.
- Prepare the Measurement
- Select the wavelength of the light source you wish to monitor using your power meter controller (e.g., Thorlabs PM400) or software.
- Zero the sensor to ensure accurate readings.
- Record the power output
- Turn on the light source to 0%, 10, 20, 30…, 100%
- Record the power output for each input
- Repeat for Multiple Light Sources
- Repeat steps 3 to 4 for each light source you wish to measure.
Results
For each light source plot the measured power output (mW) function of the input (%). The excel file provides a template that can be filled in Illumination Power Linearity_Template.xlsx
Calculate the relative power: Relative Power = Power/MaxPower and plot the Relative Power (%) function of the input (%).
Calculate the curve equation (usually a linear equation : Output = K x Input). report the Slope and the R2 coefficient of dertermination (closest to 1).
Illumination Input-Output Linearity | ||
Slope | R2 | |
385nm | 0.9969 | 1 |
475nm | 0.9984 | 1 |
555nm | 1.0012 | 1 |
630nm | 1.0034 | 1 |
Conclusion
The light sources are highly linear.
Objectives and cubes transmittance
Since we are using a power meter we can easily assess the transmittance of the objectives and the filter cubes. This measure compares the power output when different objectives and cubes are in the light path. It evaluates the transmittance of each objective and compares it with the manufacturer specifications. It can detect defects or dirt on objectives.
Objectives transmittance
Acquisition Protocol
- Warm up the system
- Setup the Power Meter
- Place a power meter sensor (e.g., Thorlabs S170C) on the stage.
- Center the sensor under a low magnification objective.
- Prepare the Measurement
- Select the wavelength of the light source you wish to monitor using your power meter controller (e.g., Thorlabs PM400) or software.
- Zero the sensor to ensure accurate readings.
- Record the power output
- Turn on the light source to 100%
- Record the power output for each objective as well as without any objective
- Repeat for Multiple Light Sources
- Repeat steps 3 to 4 for each light source you
Results
For each objective plot the measured power output (mW) function of the wavelength (nm). The excel file provides a template that can be filled in Objective and cube transmittance_Template.xlsx
Calculate the relative transmittance: Relative Transmittance = Power/PowerNoObjective and plot the Relative Transmittance (%) function of the wavelength (nm).
Calculate the average transmittance for each objective.
Average transmittance | |
2.5x-0.075 | 77% |
10x-0.25 Ph1 | 60% |
20x-0.5 Ph2 | 62% |
63x-1.4 | 29% |
Compare the average transmittance to the specification provided by the manufacturer.
Specification [400-750] | Average transmittance [470-630] | |
2.5x-0.075 | >90% | 84% |
10x-0.25 Ph1 | >80% | 67% |
20x-0.5 Ph2 | >80% | 68% |
63x-1.4 | >80% | 35% |
Here we see that the measurements are close to the specification at the exception of the 63x-1.4 objective. This is expected because the 63x objective has a smaller back aperture which reduces the amount of light received.
Conclusion
The objectives are transmitting light properly.
Cubes transmittance
Acquisition Protocol
- Warm up the system
- Setup the Power Meter
- Place a power meter sensor (e.g., Thorlabs S170C) on the stage.
- Center the sensor under a low magnification objective.
- Prepare the Measurement
- Select the wavelength of the light source you wish to monitor using your power meter controller (e.g., Thorlabs PM400) or software.
- Zero the sensor to ensure accurate readings.
- Record the power output
- Turn on the light source to 100%
- Record the power output for each filter cube
- Repeat for Multiple Light Sources
- Repeat steps 3 to 4 for each light source you
Results
For each cube plot the measured power output (mW) function of the wavelength (nm). The excel file provides a template that can be filled in Objective and cube transmittance_Template.xlsx
Calculate the relative transmittance: Relative Transmittance = Power/PowerObjective and plot the Relative Transmittance (%) function of the wavelength (nm).
Report the transmittance of the appropriate wavelenth for each filter cube.
Transmittance | |
DAPI/GFP/Cy3/Cy5 | 100% |
DAPI | 14% |
GFP | 47% |
DsRed | 47% |
DHE | 0% |
Cy5 | 84% |
- The DAPI cube only transmits 14% of the excitation light compared to the Quad Band Pass DAPI/GFP/Cy3/Cy5. It is usable but will provide a low signal. This likely because of the excitation filter within the cube is not properly matching the light source. This filter could be removed since an excitation filter is already included within the light source.
- The GFP and DsRed cubes transmit 47% of the excitation light compared to the Quad Band Pass DAPI/GFP/Cy3/Cy5 transmits. It works properly.
- The DHE cube does not transmit any light from the colibri. This cube could be removed and stored.
- The Cy5 cube transmit 84% compared to the Quad Band Pass DAPI/GFP/Cy3/Cy5. It works properly.
Conclusion
Actions have to be taken for the DAPI and DHE.
XYZ Drift
This experiment evaluates how stable is the system in XY and Z. As mentioned earlier, when starting an instrument, it takes time to reach a stable steady state. This duration is known as the warmup period. It is critical to record a warmup kinetic at least once to accurately define this period.
Acquisition protocol
- Place 1 um diameter fluorescent beads (TetraSpec Fluorescent Microspheres Size Kit mounted on slide) on the stage.
- Center the sample under a high NA dry objective.
Choose an imaging channel (exemple Cy5)
Acquire a large Z-stack every minute for 24 h
It is very important to anticipate a drift in Z ie: to acquire a z-stack that is much larger than the visible bead (20 um)
Results
Use TrackMate Plugin for FIJI to detect the spot and tack it over time. DoG Spot detection with 1 um object detection, 20 quality threshold with sub-pixel localization. Detected spots coordinates were exported and displacement from the initial image was calculated in nm. The excel file provides a template to measure XYZ Drift over time XYZ Drift Kinetic_Template.xlsx
Calculate the relative displacement in X, Y and Z: Relative Displacement = Position - PositionInitial and plot the relative displacement over time.
We observe an initial drift that stabilizes over time in X (+3.5 um), Y (+1 um) and Z (-12 um).
Calculate the displacement Displacement = Sqrt( (X2-X1)2 + (Y2-Y1)2) + (Z2-Z1)2 ) and plot the displacement over time.
Calculate the resolution of your imaging configuration, Resolution = Lambda / 2*NA and plot the resolution over time (constante).
Identify visually the time when the displacement is lower than the resolution of the system. On this instrument it takes 320 min to reach its stability.
Calculate the velocity, Velocity = (Displacement2-Displacement1)/T2-T1) and plot the velocity over time.
Calculate the average velocity before and after stabilisation.
Average velocity Warmup (nm/min) | 106 |
Average velocity System Ready (nm/min) | 36 |
Conclusion
The warmup time for this specific instrument is quite long 5 hours. The average displacement velocity after warmup is 36 nm/min which is acceptable.
XYZ Repositioning accuracy
This experiment evaluates how accurate is the system in XY by measuring the accuracy of repositioning. Several variables can affect repositioning accuracy: i) Time, ii) Traveled distance and iii) Speed.
Acquisition protocol
- Place 1 um diameter fluorescent beads (TetraSpec Fluorescent Microspheres Size Kit mounted on slide) on the stage.
- Center the sample under a high NA dry objective.
Choose an imaging channel (exemple Cy5)
Acquire a 2 position Z-stack 20 times
Repeat step 4 by moving 0 um, 1 um, 10 um, 100 um, 1 000 um, 10 000 um, 80 000um in X and Y direction
Be careful your stage might have a smaller range!
Be careful not to damage the objectives (lower the objectives during movement)
I recommend to acquire 3 dataset for each condition
Results
Use TrackMate Plugin for FIJI to detect the spot and tack it over time. DoG Spot detection with 1 um object detection, 20 quality threshold with sub-pixel localization. Detected spots coordinates were exported and displacement from the initial image was calculated in nm.
The following code can automatically process an open image in ImageJ/FIJI using the Trackmate plugin. It will save the spot detection file as a CSV.
This should create a lot of CSV Files that we need to aggregates for the following analysis.
This script should provide a csv file merged_data.csv that can be processed and summarized with a pivot table XY Repositioning Accuracy_Template.xlsx
Calculate the relative position in X, Y and Z: PositionRelative= Position - PositionInitial for each axes
Calculate the displacement Displacement = Sqrt( (X2-X1)2 + (Y2-Y1)2) + (Z2-Z1)2 ).
Calculate the resolution of your imaging configuration, Resolution = Lambda / 2*NA and plot the resolution over time (constante).
.
We observe an initial drift that stabilizes over time in X (+3.5 um), Y (+1 um) and Z (-12 um).
Calculate the displacement Displacement = Sqrt( (X2-X1)2 + (Y2-Y1)2) + (Z2-Z1)2 ) and plot the displacement over time.
Calculate the resolution of your imaging configuration, Resolution = Lambda / 2*NA and plot the resolution over time (constante).
Identify visually the time when the displacement is lower than the resolution of the system. On this instrument it takes 320 min to reach its stability.
Calculate the velocity, Velocity = (Displacement2-Displacement1)/T2-T1) and plot the velocity over time.
Calculate the average velocity before and after stabilisation.
Average velocity Warmup (nm/min) | 106 |
Average velocity System Ready (nm/min) | 36 |
Conclusion
The warmup time for this specific instrument is quite long 5 hours. The average displacement velocity after warmup is 36 nm/min which is acceptable.
References
The information provided here is inspired by the following references:
doi.org/10.17504/protocols.io.5jyl853ndl2w/v2
https://doi.org/10.1083/jcb.202107093
What need to be assessed?
Resolution
Fiel Illumination Uniformity
Channel alignement (Co-registration)
Stage drift
Stage repositioning accuracy
Detector Noise