(462 days)
VirtuOst uses data from computed tomography scans to estimate bone mineral density, bone strength, and a load-to-strength ratio. This information can be used by a physician to assess fracture risk, identify osteoporosis, and monitor therapy. For pediatric patients, VirtuOst provides these estimates without any classifications and should be used only when the benefit of obtaining these estimates outweighs the risk of radiation.
VirtuOst is a software-only medical device that analyzes data in computed tomography (CT) scans to measure bone mineral density (BMD), bone strength, and a load-to-strength ratio at the proximal femur and vertebral body. BMD is measured from both a 2D projection (in g/cm2) and a volumetric scan reconstruction (in mg/cm³) of the CT scan. VirtuOst measurements can be used by a physician to identify osteoporosis, assess fracture risk, and monitor therapy. The VirtuOst analysis is performed on previously physician-acquired image data and is unrelated to acquisition equipment and clinical workstations.
1. Table of Acceptance Criteria and Reported Device Performance
| Feature/Metric | Acceptance Criteria | Reported Device Performance |
|---|---|---|
| Hip Areal BMD Equivalence (Modified Device vs. DXA) | Standard error of the regression ≤ 0.051 g/cm² for femoral neck areal BMD. | For the subject device, the standard error of the regression for femoral neck areal BMD was 0.048 g/cm² (overall). Stratified results were 0.044 g/cm² for women (N=244) and 0.051 g/cm² for men (N=80). All met the acceptance criterion. |
| Phantomless Calibration (Fat/Air vs. External Phantom) | Mean values of measurements from fat/air phantomless calibration and external phantom calibration are not significantly different (p>0.05) and show a high degree of agreement (e.g., R² close to 1) with no fixed or proportional bias. | Mean values of measurements using the two calibration methods were not significantly different (p>0.05) and showed a high degree of agreement (R² = 0.98-0.99) with no fixed or proportional bias. |
| CT-to-DXA Areal BMD Conversion for Hip (T- and Z-scores) | Standard error of the regression of less than 0.051 g/cm² for the updated sex-specific conversion equations. | The standard errors for the new sex-specific equations ranged from 0.025-0.047 g/cm², which were considered acceptable and met the criterion. |
| Slice Spacing Adjustment for Femurs Effectiveness | Measurements from images with thin and thick slice spacing are highly correlated (R > 0.98). Adjustments lead to measurements equivalent to 1.25 mm scans. No evidence of a slice spacing effect on hip fracture prediction. | Measurements from images with thin and thick slice spacing were highly correlated (R > 0.98). The adjustments resulted in equivalent measurements. An observational study demonstrated that hazard ratios for hip fracture using femoral strength or hip areal BMD from VirtuOst were at least as good as DXA, and there was no evidence of a slice spacing effect on these results. |
| Non-clinical Software Functionality | All software requirements are met. The device performs as intended for all modified functionalities. | Automated unit and regression testing, as well as manual component testing (black box testing), confirmed that software requirements were met and the device performed as intended for all modified functionalities (worklist, new input types, improved femoral head segmentation, fat/air calibration, slice spacing adjustments, range checks, results report elements, DICOM output). All tests passed. |
2. Sample Sizes Used for the Test Set and Data Provenance
- Hip Areal BMD Equivalence:
- Test Set Size: 324 women and men (overall). Specifically, 244 women and 80 men.
- Data Provenance: Not explicitly stated, but implies clinical data. Retrospective or prospective is not specified.
- Phantomless Calibration:
- Development of reference data for visceral fat attenuation: 268 patients and a custom torso phantom scanned on 31 and 35 different CT scanners respectively.
- Comparison of fat/air phantomless calibration vs. phantom calibration: 40 independent patient CT scans.
- Data Provenance: Not explicitly stated, but implies clinical data from various CT manufacturers (GE Healthcare, Siemens Medical Solutions, Philips Healthcare, Toshiba International) at various settings (80-140 kVp). Retrospective or prospective is not specified.
- CT-to-DXA Areal BMD Conversion for Hip:
- Test Set Size: 200 subjects scanned on both CT and DXA.
- Data Provenance: Not explicitly stated, but implies clinical data. Retrospective or prospective is not specified.
- Slice Spacing Adjustment for Femurs:
- Development of adjustments: Pairs of CT images (unspecified number).
- Observational study: 2,783 women and men (1,306 with hip fracture). This was a case-cohort study design.
- Data Provenance: Not explicitly stated, but implies clinical data. The observational study implies retrospective data.
3. Number of Experts Used to Establish Ground Truth for the Test Set and Their Qualifications
The document does not describe the use of human experts to establish ground truth for the test sets. Instead, it relies on:
- Clinical reference standards: FDA-cleared DXA devices for hip areal BMD equivalence.
- External calibration phantoms: For validating phantomless calibration.
- Outcomes data: Hip fracture prediction in an observational study for slice spacing adjustment.
- Regression analysis and statistical comparison: For quantitative metrics.
4. Adjudication Method for the Test Set
Not applicable, as expert adjudication was not used to establish ground truth. Ground truth was based on objective measurements from clinical reference standards (DXA, external phantoms) or clinical outcomes.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study
No MRMC comparative effectiveness study involving human readers with and without AI assistance was mentioned. The study focused on the equivalence of the device's measurements to established clinical standards (DXA, phantom) and its ability to predict outcomes, rather than human reader performance improvement.
6. Standalone (Algorithm Only) Performance Study
Yes, the studies presented primarily demonstrate the standalone performance of the VirtuOst algorithm.
- The comparison of hip areal BMD measurements to DXA devices is a standalone assessment.
- The phantomless calibration validation compares the algorithm's output to a known standard (external phantom).
- The CT-to-DXA conversion study assesses the algorithm's ability to produce DXA-equivalent T- and Z-scores.
- The slice spacing adjustment validation and the observational study on hip fracture prediction also assess the algorithm's standalone performance in providing clinically relevant measurements.
7. Type of Ground Truth Used
The ground truth used was a combination of:
- Clinical reference standards: Measurements from FDA-cleared DXA devices for hip areal BMD.
- Physical standards: External calibration phantoms for validating phantomless calibration.
- Outcomes data: Hip fracture occurrence in a case-cohort study for evaluating the slice spacing adjustment and overall clinical utility.
- Regression analysis and statistical comparison: Used to define the relationship between the device's measurements and the chosen ground truths.
8. Sample Size for the Training Set
The document does not explicitly state the sample sizes used for training the VirtuOst algorithm. The information provided relates to testing and validation of the modified device.
9. How the Ground Truth for the Training Set Was Established
The document does not provide details on how the ground truth for the training set was established. The studies described are primarily focused on the validation of the modified device's performance against established benchmarks and clinical data, rather than the initial development and training of the core algorithms. It is implied that the predicate device (K113725) was developed and trained prior to this submission, and this submission focuses on demonstrating that modifications have not negatively impacted safety or effectiveness.
§ 892.1170 Bone densitometer.
(a)
Identification. A bone densitometer is a device intended for medical purposes to measure bone density and mineral content by x-ray or gamma ray transmission measurements through the bone and adjacent tissues. This generic type of device may include signal analysis and display equipment, patient and equipment supports, component parts, and accessories.(b)
Classification. Class II.