External Skin Markers Research Articles

Non-Invasive Targeted Hepatic Irradiation and SPECT/CT Functional Imaging to Study Radiation-Induced Liver Damage in Small Animal Models.

Radiation therapy (RT) has traditionally not been widely used in the management of hepatic malignancies for fear of toxicity in the form of radiation-induced liver disease (RILD). Pre-clinical hepatic irradiation models can provide clinicians with better understanding of the radiation tolerance of the liver, which in turn may lead to the development of more effective cancer treatments. Previous models of hepatic irradiation are limited by either invasive laparotomy procedures, or the need to irradiate the whole or large parts of the liver using external skin markers. In the setting of modern-day radiation oncology, a truly translational animal model would require the ability to deliver RT to specific parts of the liver, through non-invasive image guidance methods. To this end, we developed a targeted hepatic irradiation model on the Small Animal Radiation Research Platform (SARRP) using contrast-enhanced cone-beam computed tomography image guidance. Using this model, we showed evidence of the early development of region-specific RILD through functional single photon emission computed tomography (SPECT) imaging.

Actual target coverage after setup verification using surgical clips compared with external skin markers in postoperative breast cancer radiation therapy

PurposeAfter changing from offline setup verification to online setup verification using external skin markers in breast cancer patients, we noticed an increase in localized acute skin toxicity beneath the markers. Also, in vivo 3-dimensional dose measurements showed deviations between the delivered and the planned dose distributions; therefore, we investigated the accuracy of setup verification using surgical clips in the tumor bed, with a focus on target coverage of whole breast and tumor bed. Methods and materialsOrthogonal kilovoltage images were acquired before every fraction in 35 breast cancer patients, deriving an online 3-dimensional setup error by matching on external skin markers. In retrospect, a rematch was performed using surgical clips. For 155 fractions (ie, 5-6 fractions/patient), a cone beam computed tomography (CT) scan was available. Analysis concerned: (1) visibility of the clips, (2) migration of the clips, (3) comparison of setup errors according to both match methods, and (4) comparison of target coverage by recalculating the dose on the online setup-corrected cone beam CT scan with the patient setup according to both match methods. External validation of the surgical clip–based online setup verification was performed in 23 patients by analyzing kilovoltage images of 100 fractions, obtained after treatment. ResultsAll types of surgical clips could be visualized. The clip to center-of-mass distance decreased on average by 2 mm (standard deviation, 1) over the course of treatment. Setup differences between match methods were on average <0.5 mm in all directions. The reconstructed dose distributions showed standard deviations of volumes receiving 95% or 107% of prescribed dose and mean dose of the breast and boost planning target volume were similar for the planning CT and the cone beam CTs, for both match procedures. An external validation in 23 patients showed reassuring setup errors <2 mm. ConclusionsOnline setup verification using surgical clips results in comparable setup corrections and target volume coverage as verification using skin markers. By omitting skin markers acute skin toxicity beneath the markers is prevented.

Assessment of fiducial markers to enable the co-registration of photographs and MRI data

PurposeTo investigate the visualisation of novel external fiducial skin markers in photography and MRI. To co-register photographs and MR images, and additionally assess the spatial accuracy of these co-registrations with the view of future application in the investigation of forensically relevant soft tissue lesions. Methods and materialsStrand-shaped fiducial markers were secured externally over hematomas on the thigh of 10 volunteers. The region of interest was photographed and examined using MRI at 3T in oblique and transversal orientations and the visibility of the markers assessed. Markers provided ‘control points’ in both sets of images, enabling the computation of an affine transform to register oblique MR images to photographs. The fiducial registration error was evaluated by calculating the root-mean-square error of nine corresponding evaluation points visible in both modalities. ResultsFiducial markers were clearly visualised in both photography and MRI. The co-registration of photographs and oblique MR images was achieved for all participants. The overall root-mean-square error for registrations was 1.18mm (TIRM) and 1.46mm (TSE2D with SPAIR fat-suppression). ConclusionsThe proposed approach led to the successful visualisation of non-invasive fiducial markers using photography and MRI (TIRM and TSE2D (SPAIR) sequences). This visualisation, combined with an affine transformation process provided a simple, cost-effective way to accurately co-register photographs and MR images of subcutaneous hematomas located on the thigh. Further investigation of the novel markers and the proposed co-visualisation approach holds potential to improve not only the forensic documentation of soft tissue lesions, but to also improve certain clinical applications, including the area of dermatology.

DEVELOPMENT OF 3D GAIT ANALYZER SOFTWARE BASED ON MARKER POSITION DATA

Human walking analysis is instrumental in medical rehabilitation because it provides quantitative information of human body segment during walking. The present work is a part of a research on the development of 3D gait analyzer software. The software consists of a program to process and display 3D kinematics and kinetics parameters of human gait based on position of external skin markers as a function of time in X, Y, Z axis and anthropometric data of a subject. To achieve good results, the marker position data is initially smoothed to eliminate noises before further processing. A graphical user interface is also constructed in this work for ease of use of the program and to enable presenting the results readily. The program developed in the present research could successfully calculate parameters of human gait such as spatio temporal parameters, linear kinematics, angular kinematics of joints, as well as ground reaction and joint forces.

Respiration-induced movement correlation for synchronous noninvasive renal cancer surgery

Noninvasive surgery (NIS), such as high-intensity focused ultrasound (HIFU)-based ablation or radiosurgery, is used for treating tumors and cancers in various parts of the body. The soft tissue targets (usually organs) deform and move as a result of physiological processes such as respiration. Moreover, other deformations induced during surgery by changes in patient position, changes in physical properties caused by repeated exposures and uncertainties resulting from cavitation also occur. In this paper, we present a correlation-based movement prediction technique to address respiration-induced movement of the urological organs while targeting through extracorporeal trans-abdominal route access. Among other organs, kidneys are worst affected during respiratory cycles, with significant three-dimensional displacements observed on the order of 20 mm. Remote access to renal targets such as renal carcinomas and cysts during noninvasive surgery, therefore, requires a tightly controlled real-time motion tracking and quantitative estimate for compensation routine to synchronize the energy source(s) for precise energy delivery to the intended regions. The correlation model finds a mapping between the movement patterns of external skin markers placed on the abdominal access window and the internal movement of the targeted kidney. The coarse estimate of position is then fine-tuned using the Adaptive Neuro-Fuzzy Inference System (ANFIS), thereby achieving a nonlinear mapping. The technical issues involved in this tracking scheme are threefold: the model must have sufficient accuracy in mapping the movement pattern; there must be an image-based tracking scheme to provide the organ position within allowable system latency; and the processing delay resulting from modeling and tracking must be within the achievable prediction horizon to accommodate the latency in the therapeutic delivery system. The concept was tested on ultrasound image sequences collected from 20 healthy volunteers. The results indicate that the modeling technique can be practically integrated into an image-guided noninvasive robotic surgical system with an indicative targeting accuracy of more than 94%. A comparative analysis showed the superiority of this technique over conventional linear mapping and modelfree blind search techniques.

An objective evaluation of a segmented foot model

Segmented foot and ankle models divide the foot into multiple segments in order to obtain more meaningful information about its functional behavior in health and disease. The goal of this research was to objectively evaluate the fidelity of a generalized three-segment foot and ankle model defined using externally mounted markers. An established apparatus that reproduces the kinematics and kinetics of gait in cadaver lower extremities was used to independently examine the validity of the rigid body assumption and the magnitude of soft tissue artifact induced by skin-mounted markers. Stance phase simulations were conducted on ten donated limbs while recording the three-dimensional kinematic trajectories of skin-mounted and then bone-mounted marker constructs. Segment kinematics were compared to underlying bone kinematics to examine the rigid body assumption. Virtual markers were calculated from the bone mounted marker set and then compared to the skin-mounted markers to examine soft tissue artifact. The shank and hindfoot segments behaved as rigid bodies. The forefoot segment violated the rigid body assumption, as evidenced by significant differences between motions of the first metatarsal and the forefoot segment, and relative motion between the first and fifth metatarsals. Motion vectors of the external skin markers relative to their virtual counterparts were no more than 3mm in each direction, and 3–7mm overall. Artifactual marker motion had mild affects on inter-segmental kinematics. Despite errors, the segmented model appeared to perform reasonably well overall. The data presented here enable more informed interpretations of clinical findings using the segmented model approach.

Cardiac image integration implications for atrial fibrillation ablation

Cardiac image registration using computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and fluoroscopy is currently being investigated and clinically used for atrial fibrillation (AF) ablation. Cardiac image registration, in the context of left atrium, is intermodal, with the acquired image and the real-time reference image residing in different image spaces, and involves optimization, where one image space is transformed into the other. Geometry-based methods, which include using fiducial points and/or surface-based techniques, are usually used for cardiac image registration. During fiducial point registration, fiducial points are either external skin markers or manually determined by marking anatomical landmarks, using mapping catheters. Usually, a minimum of three non collinear points are needed for optimal registration. Recently, a catheter placed inside the coronary sinus has also been used as a fiducial marker for the purpose of registration. During surface registration, the process involves characterizing surfaces in each of the images and deriving the best transformation between them. Unlike rigid body registration, such as has been extensively used in imaging the brain, cardiac image registration is unique and challenging. In addition to the errors inherent in intermodal registration, such as errors in pixel and voxel dimension and errors due to fiducial point selection, there are errors specific to cardiac image registration, i.e., errors due to cardiac motion during the cardiac cycle and due to respiration. This review addresses the basic principles of registration and the inherent registration errors as they relate to cardiac imaging and registration.

Cardiac image registration of the left atrium and pulmonary veins

Cardiac image registration, in the context of the left atrium, is intermodal, with the acquired image and the real-time reference image residing in different image spaces, and involves optimization, where one image space is transformed into the other. Geometry-based methods, which include using fiducial points and/or surface-based techniques, are usually used for cardiac image registration. During fiducial point registration, fiducial points are either external skin markers or manually determined by marking anatomical landmarks using mapping catheters. Usually, a minimum of three noncollinear points is needed for optimal registration. During surface registration, each of the images' surfaces are characterized to determine the best transformation between them. Unlike the rigid body registration used extensively in the study of the brain, cardiac image registration is unique and challenging. In addition to the errors inherent in intermodal registration, errors due to respiration and cardiac motion during the cardiac cycle are specific to cardiac image registration. This review addresses the basic principles of registration and the inherent registration errors as they relate to cardiac imaging and registration.

SU-FF-J-107: Extraction of Internal and External Marker 3D-Motion in Liver Patients with Compression Belt Using KV Cone-Beam Radiographic Projections

Purpose: To study correlation of internal implanted vs. external skin markers for tracking respiratory motion in liver patients using radiographic projections from on-board kV cone-beam scans. Material and Method: Cone-beam projections were analyzed to extract 3D-motion of internal and external markers for five liver patients receiving hypofractionated radiotherapy. Patients were immobilized in a stereotactic body frame and an abdominal compression belt was used to constrain respiratory motion. Marker motion was derived using a tracking algorithm and analysis of a sequence of 650 cone-beam projections acquired during a 1 minute scan. Corrections were made for imager rotation and sag. Results: External and internal markers had the same frequency of respiratory motion, however, the amplitude of external marker motion is smaller. Internal and external marker motion was also out-of-phase in some patients. Internal marker motion is greater in the superior-inferior direction than in anterior-posterior and right-left directions, which is due to compression belt constraining of respiratory motion in these direction. Two patients showed small or no motion of the external marker, whereas, internal marker motion was as large as 1.0 cm, which may be due to the proximity of the external marker to the compression belt. Conclusions: Although, the motions of internal and external markers are usually correlated and have similar motion frequency, the amplitude of marker motion may differ significantly and in some patients markers may move our-of-phase. The abdominal compression belt suppresses respiratory motion strongly normal to patient skin and may contribute to phase differences. The external markers motion for monitoring internal changes of respiration should be used with caution. Marker 3D-motion from cone-beam projections provides real time tumor trajectory that can be used to determine accuracy of PTV margins with no extra dose other than that used in CBCT imaging. Conflict of Interest: Supported by NCI Grant P01-CA59017.

Accuracy of image-guided radiotherapy of prostate cancer based on the BeamCath ® urethral catheter technique

Background and purpose To examine the accuracy of the BeamCath ® urethral catheter technique for prostate localization during radiotherapy. Materials and methods Sixty-four patients were CT scanned twice with the BeamCath ® catheter, and once without the catheter. The catheter contains radiopaque fiducial markers for prostate visualization on setup images. It is held in place by a balloon inflated with air in the bladder. The repeated CT scans were co-registered and the relative shifts of the BeamCath ® isocenter fiducial, the prostate center-of-mass, and external skin markers were evaluated. The displacement of the BeamCath ® isocenter fiducial relative to its position at the planning CT scan was also determined on setup films for 53 consecutive patients (222 setup films). Results The standard deviation (SD) of the prostate movement relative to the BeamCath ® isocenter fiducial was 0.9 mm in the left–right (LR), 2.8 mm in the cranial-caudal (CC), and 1.6 mm in the anteroposterior (AP) directions, respectively. When the balloon radius differed more than 1 mm between the CT scans (14 of 64 cases) the SD in the CC direction increased to 4.5 mm. The SD of the prostate movement relative to the pelvic bone was 0.6 mm (LR), 2.4 mm (CC), and 2.8 mm (AP), while the prostate movement relative to external skin markers was considerably larger. Removal of the catheter resulted in a mean cranial prostate movement of 1.5 mm relative to the pelvic bone. Caudal catheter displacements of 7–30 mm were observed in 5% of the setup films. In these cases, recatherization was necessary to obtain reliable prostate localization. Conclusions The BeamCath ® catheter technique markedly improved prostate localization in all directions when compared with skin markers. In the AP direction, the BeamCath ® technique was also superior to the use of bony structures. However, in the CC direction the catheter position was very vulnerable to changes in the balloon volume.

Motion detection and correction for dynamic 15O-water myocardial perfusion PET studies

Patient motion during dynamic PET studies is a well-documented source of errors. The purpose of this study was to investigate the incidence of frame-to-frame motion in dynamic ( 15)O-water myocardial perfusion PET studies, to test the efficacy of motion correction methods and to study whether implementation of motion correction would have an impact on the perfusion results. We developed a motion detection procedure using external radioactive skin markers and frame-to-frame alignment. To evaluate motion, marker coordinates inside the field of view were determined in each frame for each study. The highest number of frames with identical spatial coordinates during the study were defined as "non-moved". Movement was considered present if even one marker changed position, by one pixel/frame compared with reference, in one axis, and such frames were defined as "moved". We tested manual, in-house-developed motion correction software and an automatic motion correction using a rigid body point model implemented in MIPAV (Medical Image Processing, Analysis and Visualisation) software. After motion correction, remaining motion was re-analysed. Myocardial blood flow (MBF) values were calculated for both non-corrected and motion-corrected datasets. At rest, patient motion was found in 18% of the frames, but during pharmacological stress the fraction increased to 45% and during physical exercise it rose to 80%. Both motion correction algorithms significantly decreased (p<0.006) the number of moved frames and the amplitude of motion (p<0.04). Motion correction significantly increased MBF results during bicycle exercise (p<0.02). At rest or during adenosine infusion, the motion correction had no significant effects on MBF values. Significant motion is a common phenomenon in dynamic cardiac studies during adenosine infusion but especially during exercise. Applying motion correction for the data acquired during exercise clearly changed the MBF results, indicating that motion correction is required for these studies.

Three-dimensional relation of skin markers to lumbar vertebrae of healthy subjects in different postures measured by open MRI

The debate is to which extent external skin markers represent true underlying vertebral position and motion. Skin markers and lumbar vertebrae L3 and L4 were examined by vertically open magnetic resonance imaging (MRI) within different postures to investigate whether, and to which extent the position and orientation of skin markers represent the corresponding information of assigned underlying vertebra. Nine healthy volunteers sat within an open MRI scanner in five different seating postures: upright, low flexion, heavy flexion, upright left turn and upright right turn. Skin markers were fixed at lumbar levels L3 and L4. A set of landmarks defines corresponding positions on the vertebrae. Translation-vectors quantify the change of co-ordinates while changing position. Orientation (Cardan-angles) of each level in space was calculated from co-ordinates of three skin-markers and the corresponding vertebral landmarks respectively. The close relation between the position of the individual skin marker and its corresponding landmark on the vertebrae is conserved through all postures (regression coefficients: 0.720<b<0.972, 0.916<r<0.993, p<0.0001). Despite the high sensitivity to measurement errors there is a strong relation between the translation-vectors of external markers and the corresponding translation of the landmark on the vertebrae (0.68<r<0.99, p<0.0001). Within the resolution of the MR-imaging the orientation of the vertebrae can be predicted from the external markers (regression coefficients: 0.936<b<1.189, 0.769<r<0.959, p<0.0001). Positions and motions of skin markers can be taken as a first estimate to calculate the position and spatial orientation of underlying vertebrae. The use of skin markers may help to investigate spinal positions in daily life situations where internal imaging is not possible.

On the influence of soft tissue coverage in the determination of bone kinematics using skin markers

Accurate measurement of underlying bone positions is important for the understanding of normal movement and function, as well as for addressing clinical musculoskeletal or post-injury problems. Non-invasive measurement techniques are limited by the analysis technique and movement of peripheral soft tissues that can introduce significant measurement errors in reproducing the kinematics of the underlying bones when using external skin markers. Reflective markers, skeletally mounted to the right hind limb of three Merino-mix sheep were measured simultaneously with markers attached to the skin of each segment, during repetitions of gait trials. The movement of the skin markers relative to the underlying bone positions was then assessed using the Point Cluster Technique (PCT), raw averaging and the Optimal Common Shape Technique (OCST), a new approach presented in this manuscript. Errors in the position of the proximal joint centre, predicted from the corresponding skin markers, were shown to be phasic and strongly associated with the amount soft tissue coverage, averaging 8.5 mm for the femur, 2.8 for the tibia and 2.0 for the metatarsus. Although the results show a better prediction of bone kinematics associated with the Optimal Common Shape Technique, these errors were large for all three assessment techniques and much greater than the differences between the various techniques. Whilst individual markers moved up to 4 mm from the optimal marker set configuration, average peak errors of up to 16, 5 and 3 mm (hip, knee and tibio-metatarsal joints respectively) were observed, suggesting that a large amount of kinematic noise is produced from the synchronous shifting of marker sets, potentially as a result of underlying muscle firing and the inertial effects of heel impact. Current techniques are therefore limited in their ability to determine the kinematics of underlying bones based on skin markers, particularly in segments with more pronounced soft tissue coverage.

Respiration tracking in radiosurgery without fiducials

In robotic radiosurgery, a focused beam of radiation is moved by a robot arm. We investigated methods for soft-tissue navigation using robotic radiosurgery. In previous work we described a method for real-time tracking based on correlation between the motion of implanted fiducial markers and external skin markers. In this work we extend our method of correlation-based tracking to tracking without implanted fiducials. We propose to use deformation algorithms on CT data sets combined with registration of digitally reconstructed radiographs and intra-treatment X-ray images to obtain intermittent information on the target location. This information is then combined with our basic correlation method to achieve real-time tracking. Our study investigates the feasibility of this approach from the point of view of computing time and required level of user interaction. The term 7D registration is coined to describe the underlying method for performing this task.

A non-invasive technique for measurement of cervical vertebral angle: report of a preliminary study.

Non-invasive methods have traditionally been used to assess spine positioning and range of motion. Recently, the use of prediction models derived from external stick markers and videographic analysis has been shown to be effective at predicting lumbosacral and segmental lumbar vertebral angles. The objective of this study was to develop a similar non-invasive method to predict cervical vertebral inclination in forward head flexion. Fourteen subjects with no history of trauma or inflammatory or arthritic disorders (mean age: 25+/-1 years) participated in this study on a voluntary basis. Radiographic and videographic measurements of four external markers (C0, C2, C6, C7) were taken for each subject at three different static head positions (neutral, and 30 degrees and 60 degrees of flexion). The data obtained from nine subjects with normal cervical configuration (lordosis) were used to develop statistical models predicting the radiographic segmental angles (dependent variables) from external markers (independent variables). A multiple regression model was developed for each vertebra (C1 to C6). These regression models predict the inclination of each cervical vertebra at three different neck angles with positional data derived from the four external skin markers. Adjusted R2 values of 0.97, 0.93, 0.93, 0.96, 0.95 and 0.89 were obtained for C1, C2, C3, C4, C5 and C6, respectively. The prediction models developed in this study can explain a large part of the variance for the relative contribution of each vertebral segment to global neck flexion and provide a greater accuracy then using external stick markers only. These models were not able to adequately predict the vertebral angular positioning of subjects presenting a cervical alordosis or kyphosis.

Registration and display of brain SPECT and MRI using external markers.

Accurate anatomical localisation of abnormalities observed in brain perfusion single-photon emission computed tomography (SPECT) is difficult, but can be improved by correlating data from SPECT and other tomographic imaging modalities. For this purpose we have developed software to register, analyse and display 99mTc-hexamethylpropyleneamine oxime SPECT and 1.0 T MRI of the brain. For registration of SPECT and MRI data external skin markers containing 99mTc (220 kBq) in 50 microliters of coconut butter were used. The software is coded in the C programming language, and the X Window system and the OSF/Motif standards are used for graphics and definition of the user interface. The registration algorithm follows a noniterative least-squares method using singular value decomposition of a 3 x 3 covariance matrix. After registration, the image slices of both data sets are shown at identical tomographic levels. The registration error in phantom studies was on average 4 mm. In the two-dimensional display mode the orthogonal cross-sections of the data sets are displayed side by side. In the three-dimensional mode MRI data are displayed as a surface-shaded 3 D reconstruction and SPECT data as cut planes. The usefulness of this method is demonstrated in patients with cerebral infarcts, brain tumour, herpes simplex encephalitis and epilepsy.