Ultrasound Registration Research Articles

Use of the NeuroMate Stereotactic Robot in a Frameless Mode for Movement Disorder Surgery

Background/Aims: To evaluate the use of the NeuroMate stereotactic robot with a novel ultrasound registration system for movement disorder surgery (MDS). Methods: Using the robot in a frameless mode, 51 patients underwent MDS. Surgical planning was carried out using MRI data obtained more than 24 h before surgery. Results: 37 out of 50 targets in the subthalamic nucleus were satisfactorily identified with a single microelectrode trajectory and the final electrode positions were at a mean distance of 1.7 mm from the calculated target. There was a significant improvement in motor scores of the Unified Parkinson’s Disease Rating Scale III (off medication) at 6 (43%) and 18 months (51.7%) compared to pre-operative scores (p < 0.05). Conclusions: The frameless robot using only MRI data can be used for MDS. The temporal separation of imaging from the surgical procedure provides additional time for detailed image analysis and planning.

Three-dimensional ultrasound-based navigation combined with preoperative CT during abdominal interventions: a feasibility study.

Three-dimensional (3D) intraoperative ultrasound may be easier to interpret when used in combination with less noisy preoperative image data such as CT. The purpose of this study was to evaluate the use of preoperative image data in a 3D ultrasound-based navigation system specially designed for minimally invasive abdominal surgery. A prototype system has been tested in patients with aortic aneurysms undergoing clinical assessment before and after abdominal aortic stent-graft implantation. All patients were first imaged by spiral CT followed by 3D ultrasound scanning. The CT volume was registered to the patient using fiducial markers. This enabled us to compare corresponding slices from 3D ultrasound and CT volumes. The accuracy of the patient registration was evaluated both using the external fiducial markers (artificial landmarks glued on the patient's skin) and using intraoperative 3D ultrasound as a measure of the true positioning of anatomic landmarks inside the body. The mean registration accuracy on the surface was found to be 7.1 mm, but increased to 13.0 mm for specific landmarks inside the body. CT and ultrasound gave supplementary information of surrounding structures and position of the patient's anatomy. Fine-tuning the initial patient registration of the CT data with a multimodal CT to intraoperative 3D ultrasound registration (e.g., mutual information), as well as ensuring no movements between this registration and image guidance, may improve the registration accuracy. Preoperative CT in combination with 3D ultrasound might be helpful for guiding minimal invasive abdominal interventions.

A Transcutaneous Bone Digitizer for Minimally Invasive Registration in Orthopedics: A Real-Time Focused Ultrasound Beam Approach

Computer-guided navigation of surgical tool position in computer-assisted orthopedic systems requires the registration of computer tomographic (CT) images with underlying bone. This process is presently performed by manually digitizing points on bone with a pointer and aligning them to a preoperative CT scan. We propose the use of ultrasound to obtain points on bone transcutaneously. A custom-made A-mode probe features a modular lens focusing system and a one-step calibration method. A stable and precise echo detection algorithm is also implemented. The accuracies of three signal detection algorithms—standard deviation, cross-correlation (XCORR) and short-time Fourier transform—were compared using a known reflected signal. XCORR showed the most accurate and stable operation. To test our method of obtaining bone surface points, a plastic model of the fourth human lumbar vertebra was CT scanned and then immersed in a water bath. Six surface registrations of the vertebra using an accurate pointing device were compared to ten registrations obtained using the US probe (using the XCORR algorithm). Student's T-test showed no significant difference in error between the two methods, proving that ultrasound registration, using our method, is equivalent to the more conventional pointer method.

Ultrasound Registration of the Bone Surface for Surgical Navigation

Objective: To allow non-invasive registration of the bone surface for computer-assisted surgery (CAS), this investigation reports the development and evaluation of intraoperative registration using 2D ultrasound (US) images. This approach employs automatic segmentation of the bone surface reflection from US images tagged with the 3D position to enable the application of CAS to minimally invasive procedures.Methods: The US-based registration method was evaluated in comparison to point-based registration, which is the predominant method in current clinical use. The absolute accuracy of the US-based registration was determined using a phantom pelvis, with fiducial registration providing the ground truth. The relative accuracy was determined by an intraoperative study comparing the US registration to the point-based registration obtained as part of the HipNav™ experimental protocol.Results: The phantom pelvis study demonstrated equivalent accuracy between point-and US-based registration under in vitro conditions. In the intraoperative study, the US-based registration was sufficiently consistent with the point-based registration to warrant larger-scale clinical trials of this non-invasive registration method.Conclusion: Ultrasound-based registration eliminates the need for physical contact with the bone surface as in point-based registration. As a result, non-invasive registration could fully unlock the potential of computer-assisted surgery, enabling development of the next generation of minimally invasive surgical procedures.

Toward a dynamic real-time intraoperative permanent prostate brachytherapy methodology

Purpose To evaluate dosimetry and source location relative to CT-based dosimetry when performing real-time dynamic permanent prostate brachytherapy (PPB) with inverse treatment planning. Methods and materials A treatment algorithm for dynamic PPB was developed using inverse treatment planning. The technique utilizes real-time transrectal ultrasound prostate imaging connected to the treatment planning software. The implementation of the plan with the Mick interstitial gun is monitored with up-to-date dosimetry assessments based on the registration of each seed when placed. Real-time dose assessment is monitored and adjustments can be made during the case, if necessary. A final OR dosimetric (OR-D) assessment based on the registered seed locations is performed. Postoperative CT scans obtained at 3 weeks are used for traditional dosimetry analysis (CT-D). A matrix algorithm was developed to match the seed locations from the ultrasound registration to that of the CT-scan parameters. Results Twenty-six consecutive patients with clinically localized prostate cancer underwent PPB using the algorithm designed for dynamic real-time planning. The OR-D identified a mean D90 of 109% (range 100–118%) whereas the mean CT-D D90 at 3 weeks was 105% (range 89–122%) (p = 0.894). Analysis of the OR-D V100 and V150 relative to the 3-week CT-dose V100 and V150 were also insignificant (p = 0.112 and 0.167, respectively). Assessment of seed locations relative to the intraoperative ultrasound and postimplant CT identified a mean root-mean-square error of 4.6 mm (0–21 mm). The mean error for the x, y, and z coordinates were 2.01 mm, 2.24 mm, and 2.85 mm, respectively. Conclusions This study reports the preliminary results of a new treatment algorithm for PPB that incorporates intraoperative inverse planning with dynamic dosimetry assessment during the case. Correlation was seen between the completed intraoperative, postimplant plan and the CT based plan at 3 weeks. Seed to seed deviations between the OR-D matched well with the CT-D. Additional study is necessary to assess whether this approach can assist in improving implant dosimetry and whether it appropriately documents the OR-dose without the need for postimplant dosimetry.

Visual user guidance for registration based on A-mode ultrasound

In this study we investigate the use of an A-Mode ultrasound probe tracked by a mechanical localizer system (MicroScribe 3D) for non-invasive transcutaneous palpation and registration of bone surface points. A CT of a femur-model has been scanned and subsequently processed by segmentation and 3D-reconstruction. During the ultrasound registration, a computer based assistance tool helped guiding the alignment of the ultrasound probe. Three different modes of registration have been compared. Process times for registration have been recorded and compared. The results for using an A-Mode ultrasound system demonstrate a translation RMS accuracy of 0.58 mm. Mean ultrasound registration time has been measured to 108 sec. for palpation of 10 bone surface points of distal part of femur.

Impact of differences in ultrasound and computed tomography volumes on treatment planning of permanent prostate implants

Both ultrasound (US) and computerized tomography (CT) images have been used in the planning of prostate interstitial therapy. Ultrasound images more clearly define the apex and capsule of the prostate, while CT images define seed positions for postimplant dosimetry. Proper registration of the US volume with the CT volume is critical to the assessment of dosimetry. We therefore compared US and CT prostate volumes to determine if differences were significant. Ten consecutive patients entered in an interstitial implant program were studied by pretreatment US. In addition, pretreatment CT scans were obtained and three physicians independently outlined the dimensions of the prostate on these images. The patients subsequently underwent placement of radioactive 125I or 103Pd. Postimplant CT images were obtained the next day and the postimplant prostate volumes were outlined by the same three physicians. Seven of 10 patients underwent late CT scans 9-14 months postimplant for comparison of preimplant and immediate postimplant CT studies. There were differences between US and CT volumes. Although the physician-to-physician variation was significant, the trends were consistent, with US prostate volume typically smaller (47%) than the preimplant CT volume and markedly smaller (120%) than the postimplant CT volume. Prostate volumes derived from late CT images did not consistently return to preimplant levels. Significant differences in volume of the prostate structure were found between US and CT images. The data suggests that: (a) Implants planned on CT tend to overestimate the size of the prostate and may lead to unnecessary implantation of the urogenital diaphragm and penile urethra. (b) Registration of initial US and postimplant CT prostate volumes required for accurate dosimetry is difficult due to the increased volume of prostate secondary to trauma. (c) Further study to determine the optimal time for the postimplant CT is necessary.

Computation of a location shift between two subsequent intravascular ultrasound registrations by cross-correlation analysis of the lumen area functions

For longitudinal studies on atherosclerosis and restenosis after angioplasty by intravascular ultrasound (IVUS), it is essential that repeated studies are performed at exactly the same location along an arterial section. In human femoral arteries, lumen and plaque area functions of two subsequent IVUS pullback maneuvers were compared by cross-correlation analysis. In cross-correlation analysis of two functions with equal abscissa values, the data sets are repetitively correlated after incremental shifts of the two functions along the abscissa. This results in multiple correlation coefficients with a maximum at the relative position where the two functions show the closest match. In group A (12 patients), both pullbacks were performed after angioplasty and in group B (17 patients) one pullback was performed before angioplasty and the second immediately after angioplasty. In group A, cross-correlation showed a shift between lumen area functions of 5 mm in one patient and no shift in the other patients. Maximum correlation coefficients in group A ranged from 0.644 to 0.978. Four patients from group B showed shifts from 2.5 to 35 mm. Maximum coefficients were significantly smaller than in group A: 0.259-0.864 ( p < 0.01). Plaque area functions in group B showed higher correlations (0.468-0.862, p = 0.034) and only two shifts. Cross-correlation of lumen and plaque area functions may be used to compute location shifts between two subsequent IVUS registrations and to correct such shifts.

Subaortic flow profiles in aortic valve disease: a two-dimensional color Doppler study.

With time-corrected color Doppler echocardiography, the aortic subvalvular spatial flow velocity profile was registered in two perpendicular planes in 10 patients with aortic valve disease and in 5 healthy control subjects. Patients with predominant aortic valve stenosis had a fairly flat profile, and the subvalvular diameter, obtained from left parasternal two-dimensional tissue imaging, provided a good estimate of the mean of the two transverse flow axes. This explains the accuracy in determination of stroke volume and aortic valve area that is reported in studies on patients with aortic valve stenosis when the continuity equation is used. However, the use of apical pulsed Doppler ultrasound registrations from the left ventricular outflow tract and parasternal two-dimensional echocardiography for flow area calculation may introduce large errors in calculated stroke volume in certain patients with aortic regurgitation and in normal subjects, because of a non-flat spatial velocity profile or an inaccurate estimate of flow area.

The use of ink jets in ultrasound registrations

The continuous ink jet method developed by Professor Hellmuth Hertz, Lund Institute of Technology, Sweden, is today used in printers that print digitally stored high-quality images rapidly and at low cost. The development started in the late 1950s when there was a need for a direct registration method for ultrasound echocardiograms. The development steps are described from the early ultrasound registrations to the true halftone printing of digital images today. Images from ultrasonic color Doppler examinations have been printed by an ink jet printer at our laboratory. The color capabilities of the printer are further illustrated by the printing of pseudo-colored gray-scale images and an image where color is used to highlight differences between two gray-scale images. The results show that the printer based on continuous ink jets is an interesting alternative to the existing hard-copy devices for medical images.

The interaction between the infant and the environment: the importance of mother-child contact after delivery.

Birth is more than just the physical beginning of a new life--it is also the start of the psychosocial development of the newborn infant together with its family. Immediately after delivery parents and infants can start to exchange signals that maybe are of major importance for this development. The early post partum period has been regarded to have great potentials and especially the mother has been regarded to play a very powerful role, whereas the infant's contribution has been accorded little discussion. The individual reactive capacity of the newborn baby and its influence on the environment can be illustrated in a number of ways. In recent years studies of fetal movements have been made by means of ultra sound registration and it has been discussed whether these are precursors of later behavior in the neonate-infant. The transition at birth can be considered either to be continuous or dis-continuous, the outcome of this discussion has great bearing on the importance of early neonate-environment interactions. Short and long term outcome of different routine care procedures around the time of delivery and transition are controversial subjects. Although several studies support the importance of early post delivery interaction, other studies do not seem to find correlations between early experiences and later developmental outcome measurements. In this paper several of these aspects will be discussed, examples from the literature given and possible clinical applications suggested, as well as their impact on the care of healthy and sick newborns and their families.

Fetal respiratory movements: Relationship to postnatal respiratory capacity

Sixty-six normal and 346 pathologic pregnancies have been investigated by means of dynamic ultrasound for determination of fetal intrauterine respiratory amplitudes in over 930 scans of 30-minute duration. Ten fetuses developed respiratory distress syndrome (RDS), and all of these showed antenatally either falling (more than 2 SD) or abnormally low thoracic and abdominal amplitudes. No fetuses with amplitude measurements within the normal range (mean +/- 2 SD) developed RDS (p less than 0.001, X2 test). In 74 women, measurement of amniotic lecithin was performed within one half hour before a dynamic ultrasound registration, predictive value, or specificity between these two methods in identifying RDS. The conclusion is that the pathogenesis of RDS may be both biochemical and biophysical, and that this new noninvasive method may easily be used as a screening test for postnatal respiratory capacity in high-risk pregnancies, since only 10 equal and regular respiratory movements are needed for this measurement.