How does scanner choice and 3D model resolution affect data accuracy?

Researchers using digital methods often collect data from 3D models at different resolutions, obtained using different scanning techniques. Although previous research has sought to understand whether scanning method and model resolution affect data accuracy, no study has systematically evaluated the sources of error associated with scanning method, data acquisition method and model resolution with the aim of providing practical recommendations about the model resolution required to yield sufficiently accurate data for specimens of given sizes. In this study, using data taken from primate specimens of three broad size categories, we test whether 3D models obtained using five different scanners (Breuckmann SmartSCAN, DAVID/HP 3D Pro S3, NextEngine 2020i, Creaform Go!Scan 20 and microCT/clinicalCT) yield accurate measurements. We assess whether caliper measurements can be used alongside measurements collected from 3D surface models, whether scanning resolution affects measurement accuracy, and how scan resolution, estimated using each scanner's proprietary software, compares to model resolution measured in a standardized way. Each scanner produces 3D models that yield accurate measurements for each size category, however, combining caliper data with those taken from digital models can be problematic. Our results indicate that the accuracy of measurements taken from 3D models depends on both object size and model resolution. Based on our findings, we recommend that small specimens should be scanned at <0.3 mm, medium specimens at 0.3-0.7 mm, and large specimens at 0.3-0.5 mm resolutions if data taken from 3D surface models are to be combined with caliper datasets. We further show, for the first time, that discrepancies in estimated final model resolution are frequently observed across software packages. We therefore recommend that researchers ensure that final model resolutions are adequate based on specimen size and are independently verified using a software package other than the scanner's proprietary software. Finally, we consider the implications of the findings that measurements obtained from surface models are variably consistent with those obtained using calipers.

Development of a hybrid atomic force microscopic measurement system combined with white light scanning interferometry.

A hybrid atomic force microscopic (AFM) measurement system combined with white light scanning interferometry for micro/nanometer dimensional measurement is developed. The system is based on a high precision large-range positioning platform with nanometer accuracy on which a white light scanning interferometric module and an AFM head are built. A compact AFM head is developed using a self-sensing tuning fork probe. The head need no external optical sensors to detect the deflection of the cantilever, which saves room on the head, and it can be directly fixed under an optical microscopic interferometric system. To enhance the system's dynamic response, the frequency modulation (FM) mode is adopted for the AFM head. The measuring data can be traceable through three laser interferometers in the system. The lateral scanning range can reach 25 mm × 25 mm by using a large-range positioning platform. A hybrid method combining AFM and white light scanning interferometry is proposed to improve the AFM measurement efficiency. In this method, the sample is measured firstly by white light scanning interferometry to get an overall coarse morphology, and then, further measured with higher resolution by AFM. Several measuring experiments on standard samples demonstrate the system's good measurement performance and feasibility of the hybrid measurement method.

Are non-radiation-based imaging modalities effective for objectively assessing and monitoring patients with pectus deformities?

A best evidence topic in thoracic surgery was written according to a structured protocol. The question addressed was 'What is the role of non-radiation-based imaging modalities in the management of pectus deformities?'. Altogether 29 papers were found using the reported search, of which 8 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. We conclude that non-radiation-based imaging modalities provide a safe and easily implemented alternative to traditional computed tomography scan assessment for pectus deformities. This is particularly true for deformities on the more severe end of the spectrum and as an aid in providing an on-going assessment tool particularly in treatment modalities requiring a high degree of compliance (external bracing or vacuum bell therapy).

Measuring the impact of surgical intervention on pediatric pectus excavatum using white light scanning.

BACKGROUND: Objective preoperative assessment of pectus excavatum (PE) deformity in patients is limited to preoperative measurement of severity using computed tomography (CT) or magnetic resonance imaging (MRI). Postoperative assessment is currently subjective as postoperative CT scans are not recommended in light of radiation exposure and high cost to families. White Light Scanning (WLS) is a novel 3D imaging modality that offers an alternative that is a quick, nonionizing, inexpensive, and safe strategy for measurement both pre- and postsurgery. Our prior investigation demonstrated the feasibility of using WLS to measure PE deformity and showed very strong correlation of a new WLS-derived PE severity index, the Hebal-Malas Index (HMI), with CT-derived HI. The purpose of this study was to demonstrate use of WLS to assess extent of correction of PE deformities after the Nuss procedure. METHODS: WLS scan data were gathered prospectively in pediatric patients with PE from 2015 to 2018. HMI was obtained from the preoperative and postoperative WLS scans. Analysis assessed the differences of preoperative and postoperative HMI. Preoperative CT-derived HI was collected from the medical record and estimated postoperative Haller Index was calculated from HMI and correlation of HMI and HI using historical data. RESULTS: A total of 71 patients received a preoperative CT scan and underwent surgery for PE. Of those, 63 (89%) received WLS preoperatively and 51 (72%) had complete preoperative and postoperative WLS data. The average postoperative decrease in the WLS-derived HMI was 0.35 (SD: 0.15) and 1.73 (SD: 1.03) in WLS-estimated HI. CONCLUSIONS: WLS is highly effective in objectively quantifying the extent of surgical correction in PE patients. LEVEL OF EVIDENCE: IV TYPE OF STUDY: Diagnostic Study.

A novel technique to measure severity of pediatric pectus excavatum using white light scanning.

BACKGROUND/PURPOSE: Computed tomography (CT) derived Haller Index (HI) remains the standard for quantifying severity in patient with pectus excavatum (PE). Optical scanning described in literature reports optimistic results and new indices that correlate with HI. This study assessed the feasibility of a handheld White Light Scanner (WLS) to obtain 3D measurements and indices of PE deformity. METHODS: From April 2015-April 2017, WLS scanning was conducted by orthotists during clinical visits. Included were children with PE up to 18 years. Analysis assessed correlation of a WLS-derived severity index, Hebal-Malas Index (HMI), with physician measured PE Depth (PED), and CT-derived HI. RESULTS: Of 195 participants, 185(94%) patients with PE were scanned and 127(69%) had complete WLS data. For 88 patients undergoing monitoring, HMI correlated with PED (r = 0.42, p = 0.004). For 39 patients with pre-operative CT, HMI demonstrated strong correlation with HI (r = 0.87, p<0.0001). CONCLUSIONS: WLS demonstrated high feasibility of scanning PE. WLS-derived HMI best correlates with HI for patients with severe pectus deformity. Our current data is suggestive that WLS is best applied for severe deformities and yet to be established for milder deformities. Future yearly WLS will provide data on deformity progression and surgical therapy. LEVEL OF EVIDENCE: IV. TYPE OF STUDY: Diagnostic Study.

Measuring the impact of brace intervention on pediatric pectus carinatum using white light scanning.

BACKGROUND: Evaluation of Pectus Carinatum (PC) deformity in patients undergoing bracing is limited to subjective assessment of the chest through physical exam and photography. White Light Scanning (WLS) is a novel 3D imaging modality and offers an objective alternative that is quick, inexpensive, and safe. We previously demonstrated the feasibility of using a WLS-derived proxy for Haller index, called the Hebal-Malas Index (HMI), in measuring the surgical correction of Pectus Excavatum. The purpose of this study was to demonstrate the use of WLS to measure the severity of pre- and postbracing intervention of PC deformities and assess corrected difference between the two scans. METHODS: We conducted a prospective review of preintervention WLS scans in pediatric patients with PC from 2015 to 2017. HMI was obtained from the preintervention and postintervention WLS scans. Analysis assessed the differences of pre- and postbracing intervention of measurements. RESULTS: Of 32 patients with both pre- and postbracing scans, 13 (34%) showed improvement of more than 10%, 21 (55%) showed slight improvement of 1%-10%, and 4 (11%) did not improve at follow-up. The average postbracing change in the WLS-derived HMI was 0.10 (SD:0.11). The average length of bracing days was 331.4 (SD: 127.3) with an average of 6.8 h worn per day. Compliance was defined as patient reported utilization of the brace. Patients who were compliant showed a significant improvement (p = 0.004) compared to those who were not compliant (Table 2). However, even patients with moderate compliance still improved in many instances. Change in height was a significant factor correlating with improvement. Children who grew more while wearing a brace showed greater improvement in their deformity. CONCLUSION: Using this technique, we have the ability to objectively quantify the impact of bracing on the severity of PC deformity and measure change in deformity over time. TYPE OF STUDY: Prospective study. LEVEL OF EVIDENCE: Level IV.