Assessing the reproducibility of quantitative ultrasound parameters with standardized coefficient of variation or intraclass correlation coefficient: a unique approach

Influence factors on registration of three-dimensional contrast-enhanced ultrasound fusion imaging in evaluating the ablative margin - A phantom study

BACKGROUND

Registration of three-dimensional contrast-enhanced ultrasound fusion imaging (3DCEUS-FI) is time-consuming to obtain high success rate.

OBJECTIVE

To investigate the influence factors on registration success rate of 3DCEUS-FI.

METHODS

Water tank phantoms were made to obtain mimicked pre- and post- radiofrequency ablation three-dimensional contrast-enhanced ultrasound (3DCEUS) and CT images. Orthogonal trials were designed according to factors including size, depth, enhancement level of mimicked tumor, diameter and number of mimicked adjacent vessels. Mimicked pre- and post-RFA 3DCEUS images of 72 trials were fused to assess ablative margin (AM) by two radiologists. With CT images as standard, 3DCEUS-FI accuracy was considered as the consistency of AM evaluation. The inter-observer agreement and the influence factors on registration success rates were analyzed.

RESULTS

The intraclass correlation coefficient (ICC) for the consistency of AM evaluation between CT and 3DCEUS-FI in x-axis, y-axis or z-axis was 0.840∼0.948 (P < 0.001). The ICC for inter-observer agreement was 0.840∼0.948 (P < 0.001). The success rates of registration within mimicked vessels with diameter of 2 mm were significantly lower than those with diameter of 3 mm and 4 mm.

CONCLUSIONS

The mimicked AM measured by 3DCEUS-FI had high accuracy and inter-observer agreement. Diameter of the mimicked adjacent vessels was significantly related to success rate of registration.

Three dimensional MRF obtains highly repeatable and reproducible multi-parametric estimations in the healthy human brain at 1.5T and 3T

Magnetic resonance fingerprinting (MRF) is highly promising as a quantitative MRI technique due to its accuracy, robustness, and efficiency. Previous studies have found high repeatability and reproducibility of 2D MRF acquisitions in the brain. Here, we have extended our investigations to 3D MRF acquisitions covering the whole brain using spiral projection k-space trajectories. Our travelling head study acquired test/retest data from the brains of 12 healthy volunteers and 8 MRI systems (3 systems at 3 T and 5 at 1.5 T, all from a single vendor), using a study design not requiring all subjects to be scanned at all sites. The pulse sequence and reconstruction algorithm were the same for all acquisitions. After registration of the MRF-derived PD T1 and T2 maps to an anatomical atlas, coefficients of variation (CVs) were computed to assess test/retest repeatability and inter-site reproducibility in each voxel, while a General Linear Model (GLM) was used to determine the voxel-wise variability between all confounders, which included test/retest, subject, field strength and site. Our analysis demonstrated a high repeatability (CVs 0.7-1.3% for T1, 2.0-7.8% for T2, 1.4-2.5% for normalized PD) and reproducibility (CVs of 2.0-5.8% for T1, 7.4-10.2% for T2, 5.2-9.2% for normalized PD) in gray and white matter. Both repeatability and reproducibility improved when compared to similar experiments using 2D acquisitions. Three-dimensional MRF obtains highly repeatable and reproducible estimations of T1 and T2, supporting the translation of MRF-based fast quantitative imaging into clinical applications.

Tibial subchondral bone mineral density: sources of variability and reproducibility

OBJECTIVES

It has been shown that subchondral bone mineral density (sBMD) measurement may be a relevant parameter of osteoarthritis (OA) progression. However, factors implicating the reproducibility and contributing to the variability of the measurement have not been fully described. Thus, the aim of this study was to explore the reproducibility of sBMD by Dual energy X-ray Absorptiometry (DXA) and to further examine its sources of variability.

METHODS

In this study, short-term, intra and inter-observer reproducibility of sBMD was examined on knee images obtained on DXA scans. The influence of software (lumbar spine and forearm modes), knee positioning (flexion or extension), site and size of regions of interest (ROI) and use of rice, on both lateral and medial tibial sBMD, were assessed. Root mean square coefficient of variation (RMS CV) and least significant changes (LSC) were calculated.

RESULTS

The short-term precision of sBMD ranged between 2.24% and 5.12% for RMS CV and between 0.053 and 0.135 g/cm(2) for LSC. Good intra-observer precision was found for knee flexion conditions whatever the software used (RMS CV ranging from 0.43 to 1.41%). The reproducibility was dependant from the ROI size (the ROI including joint space exhibiting better precision results than ROI including solely the subchondral plate). For a constant size of the ROI, the precision results were site-dependant. Inter-observer RMS CV results ranged from 0.59 to 5.01% according to ROI and software used. For the specific task of monitoring medial sBMD in the ROI including solely subchondral plate, forearm flexion condition produced the highest intra-observer and short-term precision (respectively RMS CV: 0.45% and 2.77%; LSC: 0.013 and 0.080 g/cm(2)).

CONCLUSION

Taking account into the excellent precision of the sBMD measurements expressed as RMS CV with the protocol proposed in the present study, clinical application of these measurements might be envisaged.

Reproducibility of constituent time intervals of right and left fetal modified myocardial performance indices on pulsed Doppler echocardiography: a short report

OBJECTIVE

To assess reproducibility of constituent time intervals measured by pulsed Doppler echocardiography for calculation of the right and left fetal myocardial performance indices (MPIs).

METHODS

This was a prospective study of 30 normal singleton pregnancies (19-36 weeks). In each, five different time intervals were measured from the Doppler waveform and four repeated measures were taken for each time interval. Three were from the left heart: isovolumetric contraction time (ICT), isovolumetric relaxation time (IRT) and ejection time (ET); two were from the right heart: 'a-interval' and 'b-interval'. The left and right modified MPIs (Mod-MPIs) generated by these constituent time intervals were also evaluated. Two operators evaluated the reproducibility of all measures.

RESULTS

There was generally good intra- and interobserver reproducibility for all time intervals and resultant Mod-MPIs: ICT, range, 19-43 ms with intraclass correlation coefficient (ICC), 0.91 (95% CI, 0.85-0.95); ET, range, 160-184.8 ms with ICC, 0.90 (95% CI, 0.84-0.95); IRT, range, 35.8-48.5 ms with ICC, 0.67 (95% CI, 0.52-0.81); a-interval, range 208-265 ms with ICC, 0.89 (95% CI, 0.82-0.94); b-interval, range, 163.1-188.3 ms with ICC, 0.82 (95% CI, 0.71-0.90); left Mod-MPI, range, 0.33-0.48 with ICC, 0.84 (95% CI, 0.74-0.91); right Mod-MPI, range, 0.21-0.49 with ICC, 0.82 (95% CI, 0.71-0.90). The 95% limits of agreement showed no statistically significant difference in measurements between the two examiners for all time intervals.

CONCLUSION

This is the first study to evaluate the reproducibility of the component time intervals of both right and left fetal Mod-MPIs in the second and third trimesters and supports the reproducibility of fetal functional cardiac assessment. The IRT is the main source of variation for the left Mod-MPI so should be the focus of further investigation. Even using two separate pulsed-wave Doppler gates and therefore separate cardiac cycles, the right Mod-MPI is reproducible.

Measurements of ultrasonic phase velocities and attenuation of slow waves in cellular aluminum foams as cancellous bone-mimicking phantoms

The water-saturated aluminum foams with an open network of interconnected ligaments were investigated by ultrasonic transmission technique for the suitability as cancellous bone-mimicking phantoms. The phase velocities and attenuation of nine samples covering three pores per inch (5, 10, and 20 PPI) and three aluminum volume fractions (5, 8, and 12% AVF) were measured over a frequency range of 0.7-1.3 MHz. The ligament thickness and pore sizes of the phantoms and low-density human cancellous bones are similar. A strong slow wave and a weak fast wave are observed for all samples while the latter is not visible without significant amplification (100x). This study reports the characteristics of slow wave, whose speeds are less than the sound speed of the saturating water and decrease mildly with AVF and PPI with an average 1469 m/s. Seven out of nine samples show positive dispersion and the rest show minor negative dispersion. Attenuation increases with AVF, PPI, and frequency except for the 20 PPI samples, which exhibit non-increasing attenuation level with fluctuations due to scattering. The phase velocities agree with Biot's porous medium theory. The RMSE is 16.0 m/s (1%) at n = 1.5. Below and above this value, the RMSE decreases mildly and rises sharply, respectively.

Quantitative assessment of articular cartilage with morphologic, acoustic and mechanical properties obtained using high-frequency ultrasound

Osteoarthritis (OA) is one of the most common joint diseases among adults, and its early detection is still not possible. In this study, high-frequency ultrasound and ultrasound-assisted mechanical testing systems were used to quantitatively measure the morphologic, acoustic and mechanical properties of normal and enzymatically degraded bovine articular cartilages in vitro. A total of 40 osteochondral cartilage plugs were prepared from 20 bovine patellae (n=20x2) and divided into two groups for collagenase and trypsin digestions, respectively. A high-frequency ultrasound system (center frequency: 40 MHz) was used to analyze the surface integrity (ultrasound roughness index, URI), thickness and acoustic properties of the articular cartilages before and after enzymatic degradations. Acoustic parameters included the integrated reflection coefficient (IRC) from the cartilage surface, reflection from the cartilage-bone interface (AIB(bone)), integrated attenuation (IA) and integrated backscatter (IBS) of the internal cartilage tissue. A newly developed ultrasound water jet indentation system was used to assess the mechanical properties of the cartilage samples. The results showed that the URI increased significantly (p<0.05) after collagenase digestion while no significant change (p>0.05) was found after trypsin digestion. With regard to acoustic parameters, the IRC decreased significantly (p<0.05) after collagenase digestion while no significant change (p>0.05) was found after trypsin digestion. The AIB(bone) demonstrated an insignificant change after collagenase digestion (p>0.05) but a significant decrease after trypsin digestion (p<0.05). Both enzymatic degradation groups showed insignificant differences (p>0.05) in the IA but a significant increase (p<0.05) in the IBS after both enzymatic degradations. The apparent stiffness measured by ultrasound water jet indentation suggested that articular cartilage from both groups became significantly softer (p<0.05) after the enzymatic degradations. A significant relationship was found to exist between the IRC and URI (p<0.05). This study showed that high-frequency ultrasound can be a comprehensive tool to quantitatively and systematically analyze the morphologic, acoustic and mechanical properties of articular cartilage in association with its degeneration.

Assessment of depth and degeneration dependences of articular cartilage refractive index using optical coherence tomography in vitro

In this study, optical coherence tomography (OCT) with an axial resolution of 15 mum was used to investigate the depth and degeneration dependences of the refractive index (RI) of articular cartilage collected from bovine patellae in vitro. Eighteen disks of articular cartilage with a diameter of 6.35 mm harvested from different patellae were successfully prepared. Each disk was cut into two halves and three horizontal cartilage slices (n = 18 x 2 x 3) with an approximately equal thickness of 0.5 mm were further prepared from each half disk. The cartilage slices were digested by two different enzymes, collagenase and trypsin, to disturb collagen fibrils and proteoglycans, respectively. The samples were submerged in the physiological saline and tested using OCT before and after the enzyme digestion and the RI for each specimen was calculated. The RI of articular cartilage from the superficial to deep regions was 1.361 +/- 0.032 (mean +/- SD), 1.338 +/- 0.036, and 1.371 +/- 0.041 for normal specimens; 1.357 +/- 0.036, 1.331 +/- 0.030, and 1.392 +/- 0.037 for trypsin digested specimens; and 1.361 +/- 0.032, 1.336 +/- 0.048, and 1.376 +/- 0.043 for those treated by collagenase, respectively. Two-factor repeated measure ANOVA revealed that for all the three groups of specimens, the RI in different depths was significantly different (p < 0.05). However, we found that the trypsin and collagenase treatments did not exert a significant effect on the RI (p > 0.05). The results suggested that the depth dependence of articular cartilage should be taken into account when OCT is used for related measurement.

Correlation of tibial low-frequency ultrasound velocity with femoral radiographic measurements and BMD in elderly women

The ultrasonic axial transmission technique has been proposed as a method for cortical bone characterization. Using a low enough center frequency, Lamb modes can be excited in long bones. Lamb waves propagate throughout the cortical bone layer, which makes them appealing for characterizing bone material and geometrical properties. In the present study, a prototype low-frequency quantitative ultrasonic axial transmission device was used on elderly women (n = 132) to investigate the relationships between upper femur geometry and bone mineral density (BMD) and tibial speed of sound. Ultrasonic velocities (V) were recorded using a two-directional measurement set-up on the midtibia and compared with dual-energy X-ray absorptiometry measurements and plain radiographs of the hip. Statistically significant, but weak, correlations were found between V and femoral shaft cortex thickness measured from radiographs (r = 0.20-0.26). V also correlated significantly with various BMD and bone mineral content parameters (r = 0.20-0.35). Femoral BMD and geometry were found to be significant independent predictors of V (R(2) = 0.07-0.16, p < 0.01). This study showed that femoral geometry and BMD affect significantly the axial ultrasound velocity measured at the tibia. In addition, the results confirmed, for the first time, a relationship between tibial ultrasound velocity and cortical bone thickness at the proximal femur.

Assessment of depth and degeneration dependences of articular cartilage refractive index using optical coherence tomography in vitro

Measuring the depth and degeneration dependences of articular cartilage is important for the investigation of cartilage structure and the reason behind its degeneration. In this study, optical coherence tomography (OCT) was used to investigate the depth and degeneration dependences of the refractive index (RI) of articular cartilage collected from bovine patellae in vitro. Eighteen disks of articular cartilage with a diameter of 6.35 mm harvested from different patellae were prepared. Each disk was cut into two halves and three horizontal cartilage slices (n=18 x 2 x 3) with approximately equal thickness were further prepared from each half disk. The cartilage slices were digested by two different enzymes, collagenase and trypsin, to remove collagen fibres and proteoglycans, respectively. The samples were tested using OCT before and after the enzyme digestion and the RI for each specimen was calculated. Two-factor repeated measure ANOVA showed that for all the three groups of specimens, the RI in different depths was significantly different (p0.05). However, it was revealed that the trypsin and collagenase treatments did not exert a significant effect on the RI (p0.05). The results suggested that the depth dependence of articular cartilage should be taken into account when OCT is used for related measurement.

Two-year clinical trial of oral alendronate versus intravenous pamidronate in children with osteogenesis imperfecta

A 2-year prospective, partially randomized open-label trial comparing oral alendronate with intravenous pamidronate therapy in children with OI showed equivalence in increasing total body BMD, spine BMD, and linear growth, and decreasing bone turnover and fracture incidence. Children with mild OI had greater responses than severe OI in BMD and growth.

INTRODUCTION

Bisphosphonate therapies increase BMD and may reduce fractures in children with osteogenesis imperfecta (OI). A study directly comparing oral with intravenous bisphosphonate has not been published. This clinical trial compares oral alendronate with intravenous pamidronate in children with OI using an open-label, prospective, 2-year, randomized design.

MATERIALS AND METHODS

Children over the age of 3 years were stratified by bone age, pubertal stage, and type of OI and then randomized to receive oral alendronate 1 mg/kg/day in tablet form or intravenous pamidronate, 3 mg/kg/4 months. One child was assigned to pamidronate. One child randomized to intravenous pamidronate changed to oral alendronate. Eighteen children completed 12 months of therapy: nine on oral alendronate and nine on intravenous pamidronate. Primary outcome efficacy was increase in BMD. Secondary outcomes included changes in bone turnover biomarkers, fracture incidence, and growth.

RESULTS

Total body and lumbar spine BMD increased, turnover markers decreased, and linear growth increased equivalently with oral and intravenous therapy. Fracture incidence showed a trend to decrease in both groups, with a significant decrease in fracture rates when the oral and intravenous groups were pooled. There were greater responses in BMD and growth in children with milder OI (type I) than those with more severe disease (types III and IV), but there were no significant effects of age or pubertal stage.

CONCLUSIONS

Oral and intravenous bisphosphonate therapies are equally effective in children with OI and are particularly effective in milder forms. The oral route is highly acceptable in children and has practical advantages over the intravenous route.

Compartmental bone morphometry in the mouse femur: reproducibility and resolution dependence of microtomographic measurements

Microcomputed tomography (microCT) is widely used for nondestructive bone phenotyping in small animals, especially in the mouse. Here, we investigated the reproducibility and resolution dependence of microCT analysis of microstructural parameters in three different compartments in the mouse femur. Reproducibility was assessed with respect to precision error (PE%CV) and intraclass correlation coefficient (ICC). We examined 14 left femurs isolated postmortem from two strains of mice (seven per group). Measurements and analyses were repeated five times on different days. In a second step, analysis was repeated again five times for a single measurement. Resolution dependence was assessed by high-resolution measurements (10 microm) in one strain and subsequent image degrading. Reproducibility was better in full bone compartment and in cortical bone compartment in the diaphysis (PE%CV = 0.06-2.16%) than in trabecular compartment in the distal metaphysis (PE(%CV) = 0.59-5.24%). Nevertheless, ICC (0.92-1.00) showed a very high reliability of the assessed parameters in all regions, indicating very small variances within repeated measurements compared to the population variances. Morphometric indices computed from lower- and higher-resolution images displayed in general only weak dependence and were highly correlated with each other (R2 = 0.91-0.99). The results show that parameters in the full and cortical compartments were very reproducible, whereas precision in the trabecular compartment was somewhat lower. Nevertheless, all compartmental analysis methods were very robust, as shown by the high ICC values, demonstrating high suitability for application in inbred strains, where highest precision is needed due to small population variances.

[Assessment of a matrix-based quantitative ultrasound imaging device (Beam scanner): reproducibility]

PURPOSE

A new matrix-based quantitative ultrasound (QUS) device was developed for the assessment of two parameters: BUA (Broadband Ultrasound Attenuation) and SOS (Speed Of Sound). This device, called Beam scanner, is a contact imaging device designed to evaluate the calcaneus. The aim of this preliminary study was to evaluate the reproducibility of results in a sample of patient with heterogeneous age distribution.

MATERIALS AND METHODS

Seventy-six subjects were included: 18 healthy young males, 18 healthy young women and 40 women aged over 50 years old, including 19 osteoporotic patients according to WHO criteria. Five measurements were made for each patient after foot repositioning. Short-term precision was estimated using the coefficient of variation (CV), standardized CV (SCV) and intra-class correlation coefficient (ICC).

RESULTS

SCV varied with the group of subjects between 2.0 and 4.3% for BUA, and between 3.1 and 4.5% for SOS. Mean values of BUA and SOS were statistically lower for osteoporotic women compared with healthy young women or healthy young males (p<0.001). For BUA, only SCV and ICC were better for women aged over 50 years old but without statistical difference.

CONCLUSION

This study shows that the heterogeneity of the studied sample population is not a significant factor when assessing precision. This new device has a precision similar to others QUS devices.