Worksheet 2.3: Diagnostic Target Specifications & Performance Envelope

Target Product Profile (TPP) Rigor: In medical device engineering, vague goals like "high resolution" or "good accuracy" result in project failure. Specifications must be:

Quantitative: State exact physical numbers with standard units (e.g. \(1.2 \text{ mm isotropic}\), \(250 \text{ Hz}\), \(>92\% \text{ sensitivity}\)).
Bounded by Trade-offs: High spatial resolution degrades temporal resolution and SNR (\(\text{SNR} \propto \Delta x \Delta y \Delta z \sqrt{T_{\text{acq}}}\)).
Contextualized by Bayesian Prevalence: In a screening population where disease prevalence is 2%, a 90% specific test generates 5 times more false alarms than true positives!

1 Operational Setting & Clinical Intended Use

Bound where and how your proposed neuroengineering system will be deployed.

Team / Project Identifier

Team Members & Engineering Leads

Deployment Environment & Form Factor

FDA Indication for Use (Intended Patient Population)

2 Interactive Diagnostic Performance Calculator (Bayesian 2x2 Matrix)

Adjust the sliders below to explore how clinical disease prevalence interacts with your target sensitivity and specificity to govern Positive Predictive Value (PPV) and Negative Predictive Value (NPV).

Target Disease Prevalence (P) 15.0%

Clinic prevalence in tested cohort

Target Diagnostic Sensitivity (TPR) 92.0%

True positive rate: TP / (TP + FN)

Target Diagnostic Specificity (TNR) 95.0%

True negative rate: TN / (TN + FP)

Hypothetical Cohort Size (N) 1,000 pts

Expected 2×2 Contingency Outcomes (Per 1,000 Patients)

Disease (+)

Disease (−)

Test (+)

True Pos (TP) 138

False Pos (FP) 43

Test (−)

False Neg (FN) 12

True Neg (TN) 808

Positive Predictive Value (PPV)

76.2%

Negative Predictive Value (NPV)

98.5%

Likelihood Ratio (+) [LR+]

18.4

Likelihood Ratio (−) [LR−]

0.08

Bayesian Clinical Note: With a prevalence of 15.0%, approximately 3 out of every 4 positive tests represent true disease cases (PPV = 76.2%). If your system were deployed in general screening where prevalence drops to 1%, PPV would plummet to ~15%, causing over 5 false alarms for every real patient detected!

Clinical Rationale for Selected Sensitivity / Specificity Trade-Off

3 Spatiotemporal Resolution & Physical Bounds

Establish quantitative physical resolution boundaries dictated by your target neuropathology.

Spatial Resolution Target (Lateral \(\Delta x, \Delta y\) & Depth \(\Delta z\))

Temporal Resolution Target (\(\Delta t\) / Bandwidth)

Required Depth of Penetration

Field of View (FOV) & Coverage

Maximum Allowable Examination Time

Motion Tolerance & Artifact Budget

4 Target Product Profile (TPP) Engineering Matrix

Synthesize your system's complete performance envelope into a formal engineering matrix. Define the threshold (minimum viable specification) versus the ideal target.

Engineering Parameter	Minimum Threshold (MVP)	Ideal Target Spec	Biophysical / Clinical Rationale	Verification Method	Action

5 Regulatory Pathway & 510(k) Predicate Benchmark

Identify your anticipated FDA clearance pathway and benchmark your engineering device against a legally marketed predicate system to establish substantial equivalence.

Targeted FDA Regulatory Pathway

Anticipated Predicate Device / Regulatory Benchmark

Substantial Equivalence Comparison & Technological Characteristics

FDA Recognized Consensus Standards & Guidance

6 Phase 1 Dossier Synthesis & Self-Check

Synthesize your quantitative specification package into formal prose for Section 3 of your Phase 1 Deliverable.

Performance Envelope Summary Statement

Patient Safety, Regulatory & Biophysical Limits