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PubMed2005

Cardiac cone-beam CT volume reconstruction using ART.

Modern computed tomography systems allow volume imaging of the heart. Up to now, approximately two-dimensional (2D) and 3D algorithms based on filtered backprojection are used for the reconstruction. These algorithms become more sensitive to artifacts when the cone angle of the x-ray beam increases as it is the current trend of computed tomography (CT) technology. In this paper, we investigate the potential of iterative reconstruction based on the algebraic reconstruction technique (ART) for helical cardiac cone-beam CT. Iterative reconstruction has the advantages that it takes the cone angle into account exactly and that it can be combined with retrospective cardiac gating fairly easily. We introduce a modified ART algorithm for cardiac CT reconstruction. We apply it to clinical cardiac data from a 16-slice CT scanner and compare the images to those obtained with a current analytical reconstruction method. In a second part, we investigate the potential of iterative reconstruction for a large area detector with 256 slices. For the clinical cases, iterative reconstruction produces excellent images of diagnostic quality. For the large area detector, iterative reconstruction produces images superior to analytical reconstruction in terms of cone-beam artifacts.

Algorithms↗

PubMed1994

An artificial neural network approach to quantitative single photon emission computed tomographic reconstruction with collimator, attenuation, and scatter compensation.

A spatially variant technique for quantitative single photon emission computed tomographic (SPECT) image reconstruction using an artificial neural network (ANN) is presented. This network was developed to simultaneously compensate for collimator, attenuation, and scatter effects during the reconstruction process. The network was trained using a supervised scheme which implemented the generalized delta rule. Training ended once the mean-squared error (MSE) between the ideal and reconstructed images converged to a minimum. After training, the ANN weights were held constant and could be used to reconstruct source distributions other than those used while training. In the absence of noise when only collimator effects were present, reconstruction of a Hoffman brain phantom had a 89% reduction in MSE compared to standard filtered backprojection. When collimator-and-attenuation and collimator-attenuation-and-scatter trials were tested against filtered backprojection with Chang attenuation compensation, the corresponding ANN reconstructions demonstrated 85% and 86% decreases in MSE, respectively. With noise present, and with standard noise reduction filters implemented prior to reconstruction, the ANN reconstructions displayed up to a 50% decrease in MSE compared to filtered backprojection reconstructions for 200,000 count data. These results demonstrate that an ANN can be used to reconstruct SPECT images with improved quantitative accuracy.

Biophysical Phenomena↗

PubMed1997

Three-dimensional reconstruction of curves from pairs of projection views in the presence of error. II. Analysis of error.

We have previously described an approach to 3D intracerebral vascular reconstruction that uses an MRA as a reconstruction base. Additional vessels seen only by angiography are added by segmenting 2D curves from projection angiograms and reconstructing these curves into 3D, building upon the MRA. This paper is the second of two that discuss the specific problem of reconstructing a 3D curve from a given pair of 2D curves in the presence of error. The method presented is capable of detecting and handling many errors produced by misregistration, image distortion, or misdefinition of 2D curves. The first paper gives an algorithm. The current paper discusses factors affecting the accuracy of a reconstructed curve, with emphasis upon registration error. We analyze the spatial accuracy of a reconstructed point in terms of the relationships between pixel size, relative viewing angle, 3D point location, and registration error. We provide a theoretical framework that, given the known error properties of a registration algorithm, allows optimization of the viewing geometry so as to produce the highest precision of point reconstruction. A major focus is the effect of registration error upon the reconstruction of a curve. We subdivide registration error into two types, one of which produces smoothly continuous point placement errors and the other of which produces pixel pairing errors. We test our ability to reconstruct a 3D curve in the presence of both. Finally, we summarize approaches to other sources of error. We conclude with a list of recommendations to optimize reconstruction accuracy. When projection points are associated by the rules of epipolar geometry, viewplane point displacements should not exceed 1.5-2 mm along the axis perpendicular to epipolar planes.

Biometry↗

PubMed2003

Lung at thin-section CT: influence of multiple-segment reconstruction on image quality.

PURPOSE: To evaluate multiple-segment reconstruction to reduce cardiac-motion artifacts on thin-section computed tomographic (CT) images in the lung. MATERIALS AND METHODS: Fifty patients were enrolled in the study. All images were obtained with a scanner capable of 1-second revolution time. Routine lung thin-section CT examination was performed with images reconstructed with bone algorithm. Multiple-segment images reconstructed with lung algorithm were obtained for three levels in the left paracardiac region. Segment images were reconstructed retrospectively with data for 225 degrees rotation rather than the 360 degrees rotation used for a complete scan. To minimize differences resulting from reconstruction algorithms, additional nonsegmented reconstruction was performed with lung algorithm. Three radiologists reviewed each set of images and assigned a quality score. Multiway analysis of variance was performed to compare motion artifact reduction with 225 degrees and 360 degrees reconstructions. RESULTS: Differences were not significant (P >.05) between scores for images reconstructed with bone or lung algorithms. Differences were significant between scores for reconstructed images obtained with the combination of 360 degrees bone and 225 degrees segment algorithms (P <.001) and for those obtained with the combination of 360 degrees lung and 225 degrees segment algorithms (P <.001). CONCLUSION: Multiple-segment reconstruction of lung thin-section CT images is an effective technique for reducing cardiac-motion artifacts without increasing patient dose.

Adult↗

PubMed1998

Interpreting neuronal population activity by reconstruction: unified framework with application to hippocampal place cells.

Physical variables such as the orientation of a line in the visual field or the location of the body in space are coded as activity levels in populations of neurons. Reconstruction or decoding is an inverse problem in which the physical variables are estimated from observed neural activity. Reconstruction is useful first in quantifying how much information about the physical variables is present in the population and, second, in providing insight into how the brain might use distributed representations in solving related computational problems such as visual object recognition and spatial navigation. Two classes of reconstruction methods, namely, probabilistic or Bayesian methods and basis function methods, are discussed. They include important existing methods as special cases, such as population vector coding, optimal linear estimation, and template matching. As a representative example for the reconstruction problem, different methods were applied to multi-electrode spike train data from hippocampal place cells in freely moving rats. The reconstruction accuracy of the trajectories of the rats was compared for the different methods. Bayesian methods were especially accurate when a continuity constraint was enforced, and the best errors were within a factor of two of the information-theoretic limit on how accurate any reconstruction can be and were comparable with the intrinsic experimental errors in position tracking. In addition, the reconstruction analysis uncovered some interesting aspects of place cell activity, such as the tendency for erratic jumps of the reconstructed trajectory when the animal stopped running. In general, the theoretical values of the minimal achievable reconstruction errors quantify how accurately a physical variable is encoded in the neuronal population in the sense of mean square error, regardless of the method used for reading out the information. One related result is that the theoretical accuracy is independent of the width of the Gaussian tuning function only in two dimensions. Finally, all the reconstruction methods considered in this paper can be implemented by a unified neural network architecture, which the brain feasibly could use to solve related problems.

Action Potentials↗

PubMedDate not supplied

Biomechanical comparisons of three posterior cruciate ligament reconstruction procedures with load-controlled and displacement-controlled cyclic tests.

BACKGROUND: Biomechanical behaviors of posterior cruciate ligament reconstructions under cyclic loading have not been sufficiently clarified. HYPOTHESIS: Biomechanical behaviors of the reconstruction that involves use of flexor tendons and an Endobutton are significantly different under cyclic loading from behaviors of the two standard reconstructions in which bone-patellar tendon-bone graft is used. STUDY DESIGN: Controlled laboratory study. METHODS: In a porcine model, the tendon/Endobutton reconstruction, the tendon-bone/interference screw reconstruction, and the tendon-bone/tibial-inlay reconstruction were biomechanically compared by using two cyclic tests. In each group of 15 specimens, 5 knees underwent tensile testing without cyclic loading, and the remaining 10 underwent the same tensile test after 5000 cycles of load-controlled or displacement-controlled loading. RESULTS: At the 5000th cycle, the peak displacement or the peak load was affected by each type of cyclic loading to a significantly greater degree in the knees with the tendon/Endobutton procedure than in the knees reconstructed with the other two procedures. CONCLUSIONS: Plastic deformation occurred more easily during cyclic loading in the knees with the tendon/Endobutton reconstruction than in the knees with the tendon-bone reconstructions. CLINICAL RELEVANCE: When the tendon/Endobutton reconstruction is used, a longer period of postoperative immobilization is necessary.

Analysis of Variance↗

PubMed2004

Biomechanical rationale for development of anatomical reconstructions of coracoclavicular ligaments after complete acromioclavicular joint dislocations.

BACKGROUND: Surgical treatments of complete acromioclavicular joint dislocations replace or reconstruct the coracoclavicular ligaments with a single structure and do not account for the anatomical variance of each ligament in the design. PURPOSE: To evaluate the cyclic behavior and structural properties of an anatomic tendon reconstruction of the coracoclavicular ligament complex after a simulated acromioclavicular joint dislocation. STUDY DESIGN: Controlled laboratory study. METHODS: Cyclic loading followed by a load-to-failure protocol (simulated dislocation) of the normal coracoclavicular ligament complex was performed and repeated after an anatomic reconstruction on the same specimen (n = 9). The anatomical reconstruction consisted of a semitendinosus tendon that replicated the direction and orientation of both the trapezoid and conoid ligaments. RESULTS: The coracoclavicular ligament and anatomical reconstruction complexes had clinically insignificant (<3 mm) permanent elongation after cyclic loading. The stiffness and ultimate load of the coracoclavicular ligament complex (60.8 +/- 12.2 N/mm and 560 +/- 206 N) were significantly greater than for the anatomical reconstruction complex (23.4 +/- 5.2 N/mm and 406 +/- 60 N), respectively (P < .05). Further analysis of the complexes revealed a 40% decrease in the bending stiffness of the clavicle after the simulated dislocation and failure of the normal coracoclavicular ligament complex (P < .05), which contributed to the diminished properties of the anatomic reconstruction. CONCLUSIONS: The low level of permanent elongation after cyclic loading suggests that the anatomic reconstruction complex could withstand early rehabilitation; however, the decrease in the structural properties and stiffness of the clavicle should be considered in optimizing the anatomic reconstruction technique. CLINICAL RELEVANCE: Despite the differences compared to the normal coracoclavicular ligament complex, the anatomical reconstruction complex more closely approximates the stiffness of the coracoclavicular ligament complex than current surgical constructs, and the incorporation of biological tissue could improve the overall structural properties with healing.

Acromioclavicular Joint↗

PubMed2004

The effect of anterior cruciate ligament reconstruction on the risk of knee reinjury.

BACKGROUND: Although there is evidence that very active, young patients are better served with anterior cruciate ligament reconstruction, there is a lack of objective data demonstrating that future knee injury is prevented by these procedures. HYPOTHESIS: Anterior cruciate ligament reconstruction protects against reinjury of the knee that would require reoperation. STUDY DESIGN: Retrospective cohort study. METHODS: A cohort of 6576 active-duty army personnel who had been hospitalized for anterior cruciate ligament injury from 1990 to 1996 were identified. Using the Total Army Injury and Health Outcomes Database, the authors followed these individuals for up to 9 years and collected clinical, demographic, and occupational data. These data were evaluated with bivariate and multivariable analyses to determine the effect of anterior cruciate ligament reconstruction on the rate of knee reinjury that required operation. RESULTS: Of the 6576 study subjects, 3795 subjects (58%) underwent anterior cruciate ligament reconstruction and 2781 (42%) did not. The rate of reoperation was significantly lower among the anterior cruciate ligament reconstruction group (4.90/100 person-years) compared with those treated conservatively (13.86/100 person-years; P < .0001). Proportional hazard regression analyses adjusted for age, race, sex, marital status, education, and physical activity level confirmed that anterior cruciate ligament reconstruction was protective against meniscal and cartilage reinjury (P < .0001). Secondary medial meniscal injury was more common than secondary lateral meniscal injury (P < .003). Younger age was the strongest predictor of failure of conservative management leading to late anterior cruciate ligament reconstruction (P < .0001). CONCLUSIONS: Anterior cruciate ligament reconstruction protected against reoperation in this young, active population; younger subjects were more likely to require late anterior cruciate ligament reconstruction. CLINICAL RELEVANCE: Strong consideration should be given to anterior cruciate ligament reconstruction after anterior cruciate ligament injury in young, active individuals.

Adult↗

PubMed2005

Biomechanical analysis of a combined double-bundle posterior cruciate ligament and posterolateral corner reconstruction.

BACKGROUND: Failure to address both components of a combined posterior cruciate ligament and posterolateral corner injury has been implicated as a reason for abnormal biomechanics and inferior clinical results. HYPOTHESIS: Combined double-bundle posterior cruciate ligament and posterolateral corner reconstruction restores the kinematics and in situ forces of the intact knee ligaments. STUDY DESIGN: Controlled laboratory study. METHODS: Ten fresh-frozen human cadaveric knees were tested using a robotic testing system through sequential cutting and reconstructing of the posterior cruciate ligament and posterolateral corner. The knees were subjected to a 134-N posterior tibial load and a 5-N.m external tibial torque at multiple flexion angles. The double-bundle posterior cruciate ligament reconstruction was performed using Achilles and semitendinosus tendons. The posterolateral corner reconstruction consisted of reattaching the popliteus tendon to its femoral origin and reconstructing the popliteofibular ligament with a gracilis tendon. RESULTS: Under the posterior load, the combined reconstruction reduced posterior translation to within 1.2 +/- 1.5 mm of the intact knee. The in situ forces in the posterior cruciate ligament grafts were significantly less than those in the native posterior cruciate ligament at all angles except full extension. Conversely, the forces in the posterolateral corner grafts were significantly higher than those in the native structures at all angles. Under the external torque with the combined reconstruction, external rotation as well as in situ forces in the posterior cruciate ligament and posterolateral corner grafts were not different from the intact knee. CONCLUSIONS: A combined posterior cruciate ligament and posterolateral corner reconstruction can restore intact knee kinematics at time zero. In situ forces in the intact posterior cruciate ligament and posterolateral corner were not reproduced by the reconstruction; however, the posterolateral corner reconstruction reduced the loads experienced by the posterior cruciate ligament grafts. CLINICAL RELEVANCE: By addressing both structures of this combined injury, this technique restores native kinematics under the applied loads at fixed flexion angles and demonstrates load sharing among the grafts creating a potentially protective effect against early failure of the posterior cruciate ligament grafts but with increased force in the posterolateral corner construct.

Adult↗

PubMed2005

The posterolateral corner of the knee: repair versus reconstruction.

BACKGROUND: Injuries to the posterolateral corner of the knee are disabling. Despite improved understanding of this group of tendons and ligaments, the best surgical treatment of an unstable corner is not clear. HYPOTHESIS: Surgical repair of acute tears of the posterolateral corner has outcomes that are as good as those from reconstruction combined with an early motion rehabilitation protocol. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Sixty-three patients with 64 posterolateral corner tears were included in this study, with 39 posterolateral corner repairs and 25 reconstructions using the modified 2-tailed technique. Patients were evaluated with clinical and KT-2000 arthrometer examinations, as well as with Lysholm, International Knee Documentation Committee, and Short Form-36 scores. RESULTS: Fifty-six patients with 57 corner tears had minimum clinical follow-up of 24 months (range, 24-59 months). Acute primary repairs were performed on 35 patients, with 22 successful outcomes and 13 (37%) failures. Primary reconstructions were performed on 22 patients, with 20 successful outcomes and 2 (9%) failures. The difference in stability on clinical examination between repairs and reconstructions was significant (P < .05). Fourteen of 15 patients with failures of the primary posterolateral corner repair or reconstruction underwent successful revision reconstruction. The final patient with failure of the primary repair elected not to have a revision reconstruction. The final mean Lysholm knee score for both repair and reconstruction patients was 88.7 (range, 53-100). Final International Knee Documentation Committee objective scores yielded 14 (26%) normal, 28 (52%) near-normal, 9 (17%) abnormal, and 3 (6%) severely abnormal knees; the mean score was 60 at the most recent clinical evaluation. CONCLUSION: Results with repair followed by early motion rehabilitation have been significantly inferior when compared with results from reconstruction using the modified 2-tailed technique. The authors now use reconstruction rather than repair in the majority of patients who sustain posterolateral corner tears after high-energy injuries.

Adolescent↗

PubMed2005

Anatomical reconstruction of the lateral ligaments of the ankle with a gracilis autograft: a new technique using an interference fit anchoring system.

BACKGROUND: Few anatomical and minor invasive procedures have been reported for surgical reconstruction of the lateral ligaments to treat lateral instability of the ankle. Furthermore, there are no standards according to which ligaments should be reconstructed. HYPOTHESIS: A new technique for anatomically reconstructing the lateral ligaments of the ankle using an interference fit anchoring system and determining which ligaments need to be reconstructed according to the results of standard stress radiography of the talocrural and subtalar joints will be effective for treating lateral instability of the ankle. STUDY DESIGN: Case series; level of evidence, 4. METHODS: Twenty-one patients with lateral instability of the ankle underwent surgery using the proposed interference fit anchoring system. Standard stress radiographs of the subtalar joint were performed, and if the talocalcaneal angle was less than 10 degrees , only the anterior talofibular ligament was reconstructed; if there was a 10 degrees or greater opening of the talocalcaneal angle, both the anterior talofibular ligament and the calcaneofibular ligament were reconstructed. RESULTS: In the 17 patients who received only the anterior talofibular ligament reconstruction, the mean talar tilt angle on standard stress radiography of the talocrural joint was 14.5 degrees +/- 1.7 degrees before surgery and 2.6 degrees +/- 0.8 degrees 2 years after surgery (P < .0001). For the 4 patients who had both the anterior talofibular ligament and calcaneofibular ligament reconstructed, the mean talar tilt angle was 16.5 degrees +/- 1.5 degrees before surgery and 3.0 degrees +/- 0.5 degrees 2 years after surgery (P = .0015). The overall mean talocalcaneal angle on standard stress radiography of the subtalar joint was 11.3 degrees +/- 1.4 degrees before surgery and 3.5 degrees +/- 0.8 degrees 2 years after surgery (P = .0060). CONCLUSION: The proposed system has several advantages, including anatomical reconstruction with normal stability and range of motion restored, the need for only a small incision during the reconstruction, and sufficient strength at the tendon graft-bone tunnel junction, in comparison with the tension strength of the lateral ligaments of the ankle.

Adolescent↗

PubMed2006

In vivo kinematics of the knee after anterior cruciate ligament reconstruction: a clinical and functional evaluation.

BACKGROUND: Recent follow-up studies have reported a high incidence of joint degeneration in patients with anterior cruciate ligament reconstruction. Abnormal kinematics after anterior cruciate ligament reconstruction have been thought to contribute to the degeneration. HYPOTHESIS: Anterior cruciate ligament reconstruction, which was designed to restore anterior knee laxity under anterior tibial loads, does not reproduce knee kinematics under in vivo physiological loading conditions. STUDY DESIGN: Controlled laboratory study. METHODS: Both knees of 7 patients with complete unilateral rupture of the anterior cruciate ligament were magnetic resonance imaged, and 3D models were constructed from these images. The anterior cruciate ligament of the injured knee was arthroscopically reconstructed using a bone-patellar tendon-bone autograft. Three months after surgery, the kinematics of the intact contralateral and reconstructed knees were measured using a dual-orthogonal fluoroscopic system while the subjects performed a single-legged weightbearing lunge. The anterior laxity of both knees was measured using a KT-1000 arthrometer. RESULTS: The anterior laxity of the reconstructed knee as measured with the arthrometer was similar to that of the intact contralateral knee. However, under weightbearing conditions, there was a statistically significant increase in anterior translation of the reconstructed knee compared with the intact knee at full extension (approximately 2.9 mm) and 15 degrees (approximately 2.2 mm) of flexion. In addition, there was a mean increase in external tibial rotation of the anterior cruciate ligament-reconstructed knee beyond 30 degrees of flexion (approximately 2 degrees at 30 degrees of flexion), although no statistical significance was detected. CONCLUSION: The data demonstrate that although anterior laxity was restored during KT-1000 arthrometer testing, anterior cruciate ligament reconstruction did not restore normal knee kinematics under weightbearing loading conditions. CLINICAL RELEVANCE: Future reconstruction techniques should aim to restore function of the knee under physiological loading conditions.

Adult↗

PubMedDate not supplied

Retrospective direct comparison of three intraarticular anterior cruciate ligament reconstructions.

A long-term retrospective study (minimum 5 years) was done looking at three groups of anterior cruciate deficient knee patients using both subjective and objective anterior cruciate tests. Twenty-seven chronic anterior cruciate ligament deficient knees reconstructed with the middle third of the patellar tendon and 28 chronic anterior cruciate ligament deficient knees reconstructed with the semitendinosus tendon were included in this consecutive group of patients and were felt to be directly comparable. It was found that the chronic anterior cruciate ligament deficient group reconstructed with the semitendinosus tendon had 4 excellent, 10 good, 7 poor, and 7 failures with an objective score averaging 4.5 of a possible 12, while the comparable group reconstructed with the middle third of the patellar tendon had 16 excellent, 7 good, 3 poor, and only 1 failure with a score of 10 of a possible 12 (P less than 0.0032). For completeness sake, 20 anterior cruciate deficient knees from this group of consecutive patients that were reconstructed acutely with the semitendinosus tendon were also examined. This group had 8 excellent results, 9 good, 3 poor, and no failures with a score of 9.8 (P less than 0.03 compared to the other group using the semitendinosus tendon). This comparison between the two groups where the semitendinosus tendon was used in the anterior cruciate ligament reconstruction was made only to show the difference between studies dealing with knee reconstructions. There may be a significant difference between a study dealing with acutely reconstructed knees versus one focusing on chronically reconstructed knees, most likely because of both patient selection and time between injury and reconstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

PubMed1995

Surgical revision after failed lateral ankle reconstruction.

Ten patients were treated with revision ankle ligament reconstruction from 1989 through 1994 for recurrent symptomatic instability of the ankle after failure of a primary reconstruction. There were seven female and three male patients with an average age of 28 years. In four patients, symptoms developed shortly after the first reconstruction and in six patients, symptoms developed 56.2 months (average) after the initial reconstruction surgery. The average follow-up was 14 months after revision surgery. All patients had significant functional impairment before surgery and all failed to respond to conservative treatment, which included physical therapy and bracing. Seven revision ligament reconstructions included the use of a tendon graft, including the peroneus brevis, accessory peroneus, plantaris, and peroneus tertius. All revision procedures were modifications of the Elmslie procedure, (Sammarco-DiRaimondo). In addition, three Brostrom-Gould procedures were performed. The average follow-up was 31 months. All patients had clinical stability of the ankle following revision reconstruction. Nine patients (90%) returned to their previous functional level. After surgery, two patients had minimal pain and mononeuritis multiplex developed in one patient. The outcome of revision ankle ligament reconstruction compares favorably with reports for primary ankle reconstruction. Revision ankle reconstruction is a good procedure for selected patients. It is an appropriate option when conservative therapy fails to relieve recurrent symptoms of ankle instability following primary reconstruction.

Adolescent↗

PubMed2005

Neural network-based image reconstruction for positron emission tomography.

Positron emission tomography (PET) is one of the key molecular imaging modalities in medicine and biology. Penalized iterative image reconstruction algorithms frequently used in PET are based on maximum-likelihood (ML) and maximum a posterior (MAP) estimation techniques. The ML algorithm produces noisy artifacts whereas the MAP algorithm eliminates noisy artifacts by utilizing availableprior information in the reconstruction process. The MAP-based algorithms fail to determine the density class in the reconstructed image and hence penalize the pixels irrespective of the density class and irrespective of the strength of interaction between the nearest neighbors. A Hebbian neural learning scheme is proposed to model the nature of interpixel interaction to reconstruct artifact-free edge preserving reconstruction. A key motivation of the proposed approach is to avoid oversmoothing across edges that is often the case with MAP algorithms. It is assumed that local correlation plays a significant role in PET image reconstruction, and proper modeling of correlation weight (which defines the strength of interpixel interaction) is essential to generate artifact-free reconstruction. The Hebbian learning-based approach modifies the interaction weight by adding a small correction that is proportional to the product of the input signal (neighborhood pixels) and output signal. Quantitative analysis shows that the Hebbian learning-based adaptive weight adjustment approach is capable of producing better reconstructed images compared with those reconstructed by conventional ML and MAP-based algorithms in PET image reconstruction.

Algorithms↗

PubMed2006

Quantitative reconstruction of refractive index distribution and imaging of glucose concentration by using diffusing light.

We show that a two-step reconstruction method can be adapted to improve the quantitative accuracy of the refractive index reconstruction in phase-contrast diffuse optical tomography (PCDOT). We also describe the possibility of imaging tissue glucose concentration with PCDOT. In this two-step method, we first use our existing finite-element reconstruction algorithm to recover the position and shape of a target. We then use the position and size of the target as a priori information to reconstruct a single value of the refractive index within the target and background regions using a region reconstruction method. Due to the extremely low contrast available in the refractive index reconstruction, we incorporate a data normalization scheme into the two-step reconstruction to combat the associated low signal-to-noise ratio. Through a series of phantom experiments we find that this two-step reconstruction method can considerably improve the quantitative accuracy of the refractive index reconstruction. The results show that the relative error of the reconstructed refractive index is reduced from 20% to within 1.5%. We also demonstrate the possibility of PCDOT for recovering glucose concentration using these phantom experiments.

Algorithms↗

PubMed1999

High rate of failure of allograft reconstruction of the extensor mechanism after total knee arthroplasty.

BACKGROUND: Disruption of the extensor mechanism is an uncommon but devastating complication of total knee arthroplasty. Several techniques for reconstruction of the extensor mechanism after total knee arthroplasty have been reported, but we do not know of any study in which the results of one group's method were corroborated by a second group using the same technique. In the present series, we evaluated the results of reconstruction of the extensor mechanism with use of allograft according to the method described by Emerson et al. METHODS: Seven reconstructions of the extensor mechanism with use of a bone-tendon-bone allograft were performed with the technique of Emerson et al. in six patients. The patients were evaluated before and after the operation. The knee score according to the system of The Hospital for Special Surgery, evidence of an extensor lag, use of walking aids, and the ambulatory status of each patient were recorded. The patients were also asked about, and the medical records were reviewed for, episodes of falling related to weakness of the quadriceps after the reconstruction. The mean duration of follow-up was thirty-nine months (range, six to 115 months). As these reconstructions often fail early, the minimum duration of follow-up was six months. RESULTS: All seven reconstructions were rated as clinical failures on the basis of a persistent or recurrent extensor lag of more than 30 degrees. All but one patient needed an assistive device full time for walking, and four patients (five knees) had at least one documented episode of falling that was due to giving-way of the affected knee. Four of the reconstructions were revised; one revision was performed with use of another extensor mechanism allograft and three were performed with use of a medial gastrocnemius rotation flap. The other three clinical failures had not been revised at the time of writing. At the time of the most recent follow-up (or at the time of revision of the extensor reconstruction), the mean extensor lag was 59 degrees and the mean knee score was 52 points (a poor result). CONCLUSIONS: Undertensioning of the allograft reconstruction at the time of the operation and attenuation of the allograft both may have played a role in the inability of the patients to regain active extension of the knee postoperatively. Alternative techniques for reconstruction of the extensor mechanism or modifications of this technique should be considered in the treatment of this difficult problem.

Accidental Falls↗

PubMed2003

Coronary artery calcium scoring using ECG-gated multidetector CT: effect of individually optimized image-reconstruction windows on image quality and measurement reproducibility.

OBJECTIVE: We studied the effect of using individually optimized image-reconstruction windows on image quality and measurement reproducibility in coronary artery calcium scoring using ECG-gated multidetector CT (MDCT). SUBJECTS AND METHODS: In 50 patients, the coronary arteries were investigated twice with ECG-gated MDCT with 500-msec rotation time. Per scan, three sets of images were reconstructed, respectively, at an image-reconstruction window of 40%, 50%, and 60% of the R-R interval. Image quality was assessed, and the optimal image-reconstruction window per scan and per coronary territory was determined. The interscan variability of calcium mass measurements was calculated for different strategies (use of fixed image-reconstruction window [40%, 50%, or 60%] versus individually optimized image-reconstruction window). RESULTS: A significant improvement in image quality was obtained by selecting the best of three reconstructed data sets (mean image quality score, 4.4 vs 3.7; p < 0.001). Even with individually optimized image-reconstruction window values, we obtained high values for interscan variability (mean +/- SD, 27% +/- 22% vs 31% +/- 35% with a fixed image-reconstruction window). CONCLUSION: The use of individually optimized image-reconstruction windows leads to a significant improvement in image quality. However, interscan variability of calcium mass measurements remains high.

Aged↗