Fast Z Controls (r4.1)

FAST Z CONTROLS Panel

Overview

The FAST Z CONTROLS allow optional control of continuous (non-stepping) axial motion synchronized to an uninterrupted stream of acquired image frames. Such 'Fast Z' Image Stacks are distinct from standard ('Slow Z') Image Stacks which use discrete axial steps for each separate set of one or more image frames. Obtaining Fast Z Image Stacks is referred to as Volume Imaging. Each Fast Z Image Stack occurs during a Volume Imaging period.

Fast Z controllers are typically piezoelectric actuators. The FAST Z CONTROLS window is enabled only if a fastZControllerType is specified in the . Other fastZXXX settings in the pertain to this controller, if needed/specified - e.g. the COM port controller and the A/D and D/A channels used for controlled axial motion.

The Fast Z controller can serve double-duty as the Secondary Z Motor Controller. In such cases fastZControllerType is set to 'UseMotor2'.

ScanImage implements Fast Z Image Stacks by generating a continuous axial trajectory waveform/command of duration slightly shorter than (N * FP), where N is the number of slices in the Fast Z Image Stack and FP is the known (measured) frame period at the current scan settings. Each volume period waveform is initiated by a frame trigger signal from the resonant scanner system. The waveform is kept slightly shorter than (N * FP), to ensure the waveform is re-started by the very next frame trigger following the volume sweep.

Volume Imaging command waveform synced to scanner frame period

ScanImage allows convenient visualization of acquired data during Volume Imaging. By matching the / on the IMAGE CONTROLS to the , each of the slices in the Fast Z Image Stack can be viewed 'simultaneously'.

Channel Display figures configured to show each slice of Fast Z Image Stack

Core Controls

: If enabled, Fast Z Image Stack(s) are acquired on GRAB (LOOP) acquisitions where > 1.

: Specifies number of slices (i.e. frames) to acquire during each volume period.

: Specifies axial distance traversed between each successive slice (frame) during a volume period.
Either a positive or negative value can be specified, so motion may proceed in either axial direction

: If enabled, FastZ motor controller returns to its Home position – the initial axial position when a GRAB or LOOP was initiated – following the GRAB acquisition or each LOOP Repeat. This ensures subsequent acquisitions or Repeats traverse the same axial positions.
For LOOP acquisitions, this option should typically be enabled. If not enabled, successive Repeats will image progressively further along the axial direction specified, which is typically not desired.

: If enabled, axial position at start of image stack acquisition is taken as the center of the stack. Motor is moved backwards by half the total span implied by and prior to the start of the stack acquisition.
If is enabled and is even, then none of the frames within each volume period will be centered on the starting axial position at time of GRAB/LOOP initiation

The , , , and controls are all linked to same controls on the MOTOR CONTROLS window

/: Specifies number of FastZ Image Stacks to scan (or already scanned) during each GRAB or LOOP Repeat. For Volume Imaging acquisitions, ScanImage collects a total of x frames for each GRAB or LOOP Repeat.

Advanced Controls

: At this time, ScanImage 4.1 only supports 'XY-Z' volume imaging - i.e. axial sweeps synchronized with an integer set of image frames. In future 'XZ' and 'XZ-Y' modes may be supported, where a faster axial sweep is synchronized to an integer set of line scans.

: At this time, ScanImage 4.1 only supports 'Sawtooth' fast axial scan waveforms. In future fast stepping waveforms and/or bidirectional axial scan waveforms may be supported.

Frame Period Controls

ScanImage maintains a measured frame period value for each set of scan parameters. For Volume Imaging, the duration of axial command waveform is set slightly shorter than (N * FP) where N is and FP is the measured frame period. The is used to determine how much to shorten the axial command waveform period relative to (N * FP).

: Displays last mesasured frame period at currently set values of , , and on MAIN CONTROLS. If no measurement has been taken at this triad of current parameters, value will show NaN in red.
Frame rate MUST be measured at current parameters before start of a GRAB/LOOP acquisition
Measured value at each triad of parameters is stored across ScanImage sessions, i.e. so value need not typically be measured again. In testing thus far, scan rate stability at given settings has been quite stable.

: Measure scan frame period (average period between Frame Trigger pulse edges) at current triad of , , and values.

: Specifies amount by which to reduce frame period, compared to measured value, for each of the specified when determining duration of axial trajectory command waveform. Value is always negative.
If frame trigger adjustment is too small, frame triggers will be missed and axial waveform will become desynchronized with each volume's image slices (frames). However setting value too large results in larger error of axial position at each slice (frame).
Note that adjustment applies per slice in the Volume Imaging period, so overall reduction in axial trajectory waveform duration increases when increases. This results in somewhat larger axial position error at each slice.

Axial Scanner Physical Adjustments

Physical FastZ axial scanner devices cannot follow the exact axial trajectory command waveform supplied:
The axial scanner response will be delayed (lag) the command waveform.

For pure sawtooth scanning waveforms, the actual scanner flyback cannot be instantaneous, i.e. scanner cannot exactly follow commanded trajectory at start of each Volume Imaging period

: Specifies delay between axial scanner response and command waveform. Accurate setting of this value is required so that each slice within volume imaging period is centered on correct axial position.

- If enabled, 1 or more image frames are added to each Volume Imaging period of, with these final frame(s) intended to allow axial scanner to flyback to start of specified . These added frames will still be saved to disk, but should typically be ignored in analysis.
- If disabled, a flyback artifact will appear in image at start of (at least) the first frame in each FastZ Image Stack

: Specifies number of frames added to each Volume Imaging period, if is enabled. This value is computed automatically by ScanImage, based on the user-supplied value.

Discard Flyback options for FastZ Image Stacks with # Slices = 4

Acq Delay Adjustment Procedure

If users enable , use an odd N, and disable , then: the center of the (N+1)/2 slice (i.e. the middle frame for each volume period) should match the center of a FOCUS image acquired just before the FastZ Image Stack. The should be adjusted until this condition is achieved.

Child pages