Erratum: Toward quantitative assessment of deformational plagiocephaly and brachycephaly at the point-of-care.

[This corrects the article DOI: 10.1117/1.JMI.8.2.024504.].

Toward quantitative assessment of deformational plagiocephaly and brachycephaly at the point-of-care.

Purpose: Develop and validate algorithms that can enable a novice user to quantitatively measure the head shape parameters associated with deformational plagiocephaly and brachycephaly (DPB) using 2D rendered images. Approach: First, the head contour is extracted semi-automatically using the intelligent scissors method. We then automatically compute two indices used in the clinical determination of the DPB from the head shape parameters: the cranial index (CI) and the cranial vault asymmetry index (CVAI). We also present methods to quantify and compensate for the user variability, including camera angle and distance from the head using 2D rendered images. We compared the results of our technology with ground-truth (GT) measurements from 53 infants with DPB and normal cranial parameters. Results: The Spearman correlation coefficient between the new 2D rendered method and the 3D GT was 0.94 ( p < 0.001 ) and 0.96 ( p < 0.001 ) for CI and CVAI, respectively. Different simulated camera angles and distances from the head resulted in variation in CI and CVAI in the range of [ - 2.0 , 6.0 ] and [ - 4.0 , 4.0 ] units, respectively. The limits of agreement of the Bland-Altman test were reduced from [ - 3.6 , 5.3 ] and [ - 3.6 , 4.2 ] to [ - 0.5 , 3.0 ] and [ - 1.3 , 1.6 ] for CI and CVAI, respectively, by combining results from different camera angles and positions in our method. The overall accuracy of the proposed technology for DPB detection was 100%. Conclusions: The 2D rendered images of the head can be accurately analyzed to assess DPB. Further study on 2D photos taken from human subjects is warranted.

Enabling technologies for robot assisted ultrasound tomography.

Currently available ultrasound (US) tomography systems suggest utilizing cylindrical transducers that can be used for a specific organ. In this paper, our focus is on an alternative way of creating US tomographic images that could be used for other anatomies and more general applications. This system consists of two conventional US probes facing each other while one or several of the transducers in one probe can act as the transmitter and the rest as the receiver. Aligning the two US probes is a challenging task. To address this issue, we propose a robot assisted US tomography system in which one probe is operated freehanded and another by a robotic arm. In this paper, enabling technologies for this system are described. With the current prototype, a reconstruction precision of 4.12, 1.73, and 2.23 mm for the three calibrations, and an overall alignment repeatability in the range of 5-9 mm were achieved. Copyright © 2016 John Wiley & Sons, Ltd.

Robot-assisted automatic ultrasound calibration.

PURPOSE: Ultrasound (US) calibration is the process of determining the unknown transformation from a coordinate frame such as the robot's tooltip to the US image frame and is a necessary task for any robotic or tracked US system. US calibration requires submillimeter-range accuracy for most applications, but it is a time-consuming and repetitive task. We provide a new framework for automatic US calibration with robot assistance and without the need for temporal calibration. METHOD: US calibration based on active echo (AE) phantom was previously proposed, and its superiority over conventional cross-wire phantom-based calibration was shown. In this work, we use AE to guide the robotic arm motion through the process of data collection; we combine the capability of the AE point to localize itself in the frame of the US image with the automatic motion of the robotic arm to provide a framework for calibrating the arm to the US image automatically. RESULTS: We demonstrated the efficacy of the automated method compared to the manual method through experiments. To highlight the necessity of frequent ultrasound calibration, it is demonstrated that the calibration precision changed from 1.67 to 3.20 mm if the data collection is not repeated after a dismounting/mounting of the probe holder. In a large data set experiment, similar reconstruction precision of automatic and manual data collection was observed, while the time was reduced by 58 %. In addition, we compared ten automatic calibrations with ten manual ones, each performed in 15 min, and showed that all the automatic ones could converge in the case of setting the initial matrix as identity, while this was not achieved by manual data sets. Given the same initial matrix, the repeatability of the automatic was [0.46, 0.34, 0.80, 0.47] versus [0.42, 0.51, 0.98, 1.15] mm in the manual case for the US image four corners. CONCLUSIONS: The submillimeter accuracy requirement of US calibration makes frequent data collections unavoidable. We proposed an automated calibration setup and showed feasibility by implementing it for a robot tooltip to US image calibration. The automated method showed a similar reconstruction precision as well as repeatability compared to the manual method, while the time consumed for data collection was reduced. The automatic method also reduces the burden of data collection for the user. Thus, the automated method can be a viable solution for applications that require frequent calibrations.

Toward teleoperated needle steering under continuous MRI guidance for prostate percutaneous interventions.

BACKGROUND: To propose a human-operated in-room master-slave bevel-tip needle steering system under continuous MRI guidance for prostate biopsy, in which the patient is kept in the scanner at all times and the process of needle placement is under continuous control of the physician. METHODS: A 2-DOF MRI-compatible needle steering module is developed and integrated with an existing 4-DOF transperineal robot, creating a 6-DOF robotic platform for prostate interventions. An MRI-compatible 2-DOF master robot is also developed to enable remote needle steering. An MRI-compatible 2-DOF force/torque sensor was used on the master side. Bevel-tip needle steering is implemented in order to compensate for the targeting error due to needle-tissue interaction. RESULTS: MRI-compatibility results demonstrated maximum 20% loss in signal to noise ratio (SNR). Robot functionality was not influenced by the magnetic field. Targeting error was reduced from 4.2 mm to 0.9 mm as a result of bevel-tip needle steering. CONCLUSIONS: The feasibility of teleoperated bevel-tip needle steering using the proposed system was shown in a phantom experiment. Copyright © 2015 John Wiley & Sons, Ltd.

Surgical fiducial segmentation and tracking for pose estimation based on ultrasound B-mode images.

Doppler ultrasound is a non-invasive diagnostic tool for the quantitative measurement of blood flow. However, given that it provides velocity data that is dependent on the location and angle of measurement, repeat measurements to detect problems over time may require an expert to return to the same location. We therefore developed an image-guidance system based on ultrasound B-mode images that enables an inexperienced user to position the ultrasound probe at the same site repeatedly in order to acquire a comparable time series of Doppler readings. The system utilizes a bioresorbable fiducial and complementing software composed of the fiducial detection, key points tracking, probe pose estimation, and graphical user interface (GUI) modules. The fiducial is an echogenic marker that is implanted at the surgical site and can be detected and tracked during ultrasound B-mode screening. The key points on the marker can next be used to determine the pose of the ultrasound probe with respect to the marker. The 3D representation of the probe with its position and orientation are then displayed in the GUI for the user guidance. The fiducial detection has been tested on the data sets collected from three animal studies. The pose estimation algorithm was validated by five data sets collected by a UR5 robot. We tested the system on a plastisol phantom and showed that it can detect and track the fiducial marker while displaying the probe pose in real-time.