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The moorLDI Laser Doppler Imager is intended for studies of blood flow in the microcirculation, e.g. blood flow in the small blood vessels of the skin. It is suitable for a wide range of clinical research applications including plastic surgery, diabetes, dermatology, vascular surgery, wound healing, neurology, physiology, neurosurgery and anaesthetics.

The moorLDI laser Doppler imager is a device for imaging blood flow in the microcirculation of surface tissue e.g. blood flow in skin. It uses the established laser Doppler technique to quantify movement of blood cells beneath the skin surface. Unlike existing laser Doppler monitors, which use optical fibre probes at fixed tissue sites, moorLDI scans a low power laser beam in a raster pattern over the skin surface to build up a colour coded image of blood flow.

A beam of light from a low power HeNe red laser is directed by a moving mirror which is driven by the DC servo motors to execute a raster pattern across the tissue surface. The incident light is scattered by static tissue and by moving blood. The Doppler frequency shifted light from moving blood and non-shifted light from tissue is then directed by the same moving mirror (and focusing lenses) onto two photodiodes. Light 'beats' at the detectors due to constructive and destructive mixing of the light. These intensity fluctuation are then processed in suitable electronic circuits to give parameters of flux (proportional to tissue blood flow) and conc (proportional to the concentration of moving blood cells). The outputs of the Doppler signal processor and a DC signal (the light intensity) are sent to the computer (PC) via an opto isolated RS232 serial port, so an intensity photo image and a colour-coded blood flow image can be displayed and processed by the computer.

The moorLDI consists of a control box, scanner head and optional bench top or a mobile stand. The system interfaces with the PC via an opto isolated RS232 serial port at a baud rate of 19200. The moorLDI control box contains a power supply unit and all main electronic circuit board. The optical and mechanical components are mounted on the base plate of the scanner head. The control signals for the mirror, shutter, laser power attenuator, etc. are provided by the control box via a 37 way cable. The laser Doppler shifted signals detected by the photo detector board, which is mounted on the base plate of the scanner head, are sent to the control box via a 9 way analogue cable.

Acceptance Criteria and Study for moorLDI Laser Doppler Imager

This section outlines the acceptance criteria and the studies conducted to demonstrate that the moorLDI Laser Doppler Imager meets these criteria, supporting its substantial equivalence to predicate devices.

1. Table of Acceptance Criteria and Reported Device Performance

The provided document does not explicitly state formal, quantitative acceptance criteria in the form of a pass/fail threshold. Instead, the performance evaluation is based on demonstrating substantial equivalence to predicate devices (PIM 1.0 Laser Doppler Perfusion Imager and Moor Laser Blood Flow Monitor MBF3D) through comparable or improved performance in key areas. The "acceptance criteria" can be inferred from the performance claims made in comparison to these predicates.

2. Sample Size Used for the Test Set and Data Provenance

The document does not explicitly use the term "test set" in the context of typical machine learning or diagnostic imaging validation studies. However, the performance data presented is derived from several studies:

• Flow Model:

  • Sample Size: Not specified in terms of distinct "samples" but involved measurements across five rows of silicone tubing, using single-point and imaging modes at various cut-off frequencies and scan speeds. Multiple flow rates were tested.
  • Data Provenance: Controlled laboratory experiment using a flow simulator.

• Assessment of Movement Artefact:

  • Sample Size: Measurements taken on a forearm. Not specified number of subjects or repeated measurements from distinct individuals.
  • Data Provenance: In-vivo human forearm measurements.

• Single Point Measurements (Comparison with MBF3D):

  • Sample Size: Not specified in terms of number of subjects, but refers to "signals recorded... at the finger tip" during a pressure cuff experiment.
  • Data Provenance: In-vivo human measurements (finger tip).

• Image Scanning (Comparison with PIM 1.0):

  • Sample Size: "Images of blood flow in the dorsum of the hand were recorded." Not specified number of subjects.
  • Data Provenance: In-vivo human measurements (dorsum of hand).

• Compared with Microsphere Technique:

  • Sample Size: 12 adult male New Zealand rabbits. A total of 72 images were obtained (12 rabbits * 2 pump speeds * 3 scan rates).
  • Data Provenance: Prospective, in-vivo animal study (New Zealand rabbits). Data from J. Lockhart, W. Ferrell and W. Angerson (Int. J Microcirc, 1997; 17:130-137).

• Compared with PIM 1.0: Measurement in Knee Ligaments of Adult Rabbits:

  • Sample Size: 9 female, one-year-old, New Zealand White rabbits.
  • Data Provenance: Prospective, in-vivo animal study (New Zealand White rabbits). Data from K. Forrester, M. Doschak and R. Bray (Medical & Biological Engineering & Computing 1997, Nov).

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications

The term "experts" and "ground truth" are not applicable in the typical sense of human-labeled data for an AI system, as this device is a measurement instrument directly quantifying a biophysical phenomenon (blood flow).

• Flow Model: The "ground truth" for flow rates was established by controlling the pump speed (e.g., 2.8 ml/min and 11.0 ml/min) of a known solution through tubing. No human experts were involved in establishing this ground truth.
• Movement Artefact / Single Point Measurements / Image Scanning (Human Studies): The "ground truth" is the physiological blood flow itself, observed or assumed to be stable or to change in a predictable manner (e.g., during occlusion). No human experts were involved in establishing ground truth labels; the device measures a physical property.
• Compared with Microsphere Technique & Knee Ligaments in Rabbits: The "ground truth" was established by the radiolabelled microsphere technique, which is described as a "well-established technique for quantitative measurements of blood flow." This is a direct, quantitative measurement method. While the individuals conducting and interpreting the microsphere technique are experts in that field, they are not "experts establishing ground truth for a test set" in the context of an AI algorithm's performance against human interpretation. The reference publications would list the qualifications of the researchers/scientists involved.

4. Adjudication Method for the Test Set

Adjudication methods (e.g., 2+1, 3+1) are typically used in studies where human experts are labeling data (e.g., images for disease) and discrepancies need to be resolved. Since the "ground truth" for these studies is either a controlled physical parameter or a direct quantitative measurement by another established technique, an adjudication method for reconciling expert opinions is not applicable and was not performed.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done

No. A multi-reader multi-case (MRMC) comparative effectiveness study, which typically evaluates how much human readers improve with AI assistance, was not performed. The moorLDI is a measurement device for blood flow; it does not involve human readers interpreting its output in a diagnostic context that would be augmented by AI, nor does it present AI-derived interpretations.

6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done

Yes, the studies conducted demonstrate the standalone performance of the moorLDI device itself. The device is a direct measurement instrument, and its output (flux, etc.) is the direct result of its internal processing of physical signals. All performance data presented (linearity, correlation with microspheres, comparison with predicate devices) are evaluations of the device operating independently to produce a measurement. There is no "human-in-the-loop" component for the measurement acquisition or processing that would alter the algorithm's standalone performance.

7. The Type of Ground Truth Used

The types of ground truth used were primarily:

• Controlled Physical Parameters: In the flow model, the ground truth for blood flow was the precisely controlled flow rate of the motility standard through the tubing, governed by an infusion pump.
• Established Quantitative Measurement Technique: For in-vivo animal studies, the radiolabelled microsphere technique was used as the gold standard for quantitative blood flow measurement. This is considered an objective, established scientific method for measuring blood flow.
• Physiological Response: For human studies involving a pressure cuff, the ground truth was the expected physiological change in blood flow (occlusion and release).

8. The Sample Size for the Training Set

The concept of a "training set" is not applicable to this device. The moorLDI is a laser Doppler measurement instrument based on established physical principles (Doppler effect) and analog circuit design. It is not an AI/machine learning system that learns from a training dataset.

9. How the Ground Truth for the Training Set Was Established

As stated above, a "training set" and its associated ground truth are not applicable to the moorLDI device, as it is a physical measurement instrument and not an AI system. Its design and operational principles are based on physics and electrical engineering, not on learned patterns from a dataset.

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