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PubMed2002

Performance evaluation of OSEM reconstruction algorithm incorporating three-dimensional distance-dependent resolution compensation for brain SPECT: a simulation study.

UNLABELLED: Iterative reconstruction techniques such as an ordered subsets-expectation maximization (OSEM) algorithm can easily incorporated various physical models of attenuation or scatter. We implemented OSEM reconstruction algorithm incorporating compensation for distance-dependent blurring due to the collimator in SPECT. The algorithm was examined by computer simulation to estimate the accuracy for brain perfusion study. METHODS: The detector response was assumed to be a two-dimensional Gauss function and the width of the function varied linearly with the source-to-detector distance. The attenuation compensation (AC) was also included. To investigate the properties of the algorithm, we performed computer simulations with the point source and digital brain phantoms. In the point source phantom, the uniformity of FWHM for the radial, tangential and longitudinal directions was evaluated on the reconstruction image. As for the brain phantom, quantitative accuracy was estimated by comparing the reconstructed images with the true image by the mean square error (MSE) and the ratio of gray and white matter counts (G/W). Both noise free and noisy simulations were examined. RESULTS: In the point source simulation, FWHM in radial, tangential and longitudinal directions were 14.7, 14.7 and 15.0 mm at the image center and were 15.9, 9.83 and 10.6 mm at a distance of 15 cm from the center by using FBP, respectively. On the other hand, they were 8.12, 8.12 and 7.83 mm at the image center, and were 7.45, 7.44 and 7.01 mm at 15 cm from the center by OSEM with distance-dependent resolution compensation (DRC). An isotropic and stationary resolution was obtained at any location by OSEM with DRC. The spatial resolution was also improved about 6.5 mm by OSEM with DRC at the image center. In the brain phantom simulation, the blurring at the edge of the brain structure was eliminated by using OSEM with both DRC and AC. The G/W was 2.95 and 2.68 for noise free and noisy cases, respectively, when no compensation was performed. But the values for G/W without and with noise became 3.45 and 3.21 with AC only and were improved to 3.75 and 3.71 with both AC and DRC. The G/W approached the true value (4.00) by using OSEM with both AC and DRC even when there was statistical noise. CONCLUSION: In conclusion, OSEM reconstruction including the distance-dependent resolution compensation algorithm was reasonably successful in achieving isotropic and stationary resolution and improving the quantitative accuracy for brain perfusion SPECT.

Algorithms↗

PubMed2000

Relevant priors prefetching algorithm performance for a picture archiving and communication system.

Proper prefetching of relevant prior examinations from a picture archiving and communication system (PACS) archive, when a patient is scheduled for a new imaging study, and sending the historic images to the display station where the new examination is expected to be routed and subsequently read out, can greatly facilitate interpretation and review, as well as enhance radiology departmental workflow and PACS performance. In practice, it has proven extremely difficult to implement an automatic prefetch as successful as the experienced fileroom clerk. An algorithm based on defined metagroup categories for examination type mnemonics has been designed and implemented as one possible solution to the prefetch problem. The metagroups such as gastrointestinal (GI) tract, abdomen, chest, etc, can represent, in a small number of categories, the several hundreds of examination types performed by a typical radiology department. These metagroups can be defined in a table of examination mnemonics that maps a particular mnemonic to a metagroup or groups, and vice versa. This table is used to effect the prefetch rules of relevance. A given examination may relate to several prefetch categories, and preferences are easily configurable for a particular site. The prefetch algorithm metatable was implemented in database structured query language (SQL) using a many-to-many fetch category strategy. Algorithm performance was measured by analyzing the appropriateness of the priors fetched based on the examination type of the current study. Fetched relevant priors, missed relevant priors, fetched priors that were not relevant to the current examination, and priors not fetched that were not relevant were used to calculate sensitivity and specificity for the prefetch method. The time required for real-time requesting of priors not previously prefetched was also measured. The sensitivity of the prefetch algorithm was determined to be 98.3% and the specificity 100%. Time required for on-demand requesting of priors was 9.5 minutes on average, although this time varied based on age of the prior examination and on the time of day and database traffic. A prefetch algorithm based on metatable examination mnemonic categories can pull the most appropriate relevant priors, reduce the number of missed relevant priors, and therefore reduce the time involved for the manual task of on-demand requests of priors. Network and database traffic can be reduced as well by decreasing the number of priors selected from the archive and subsequently transmitted to the display stations, through elimination of transactions on examinations not relevant to the current study.

Algorithms↗

PubMed2006

Development of a 3-D convolution/superposition algorithm for precise dose calculation in the skull.

In this paper an algorithm for calculating 3-D dose distributions within the brain is introduced and adapted to the demands of modem radiosurgery. The dose calculation with this model is based on a 3-D distribution of the primary photon intensity which is calculated with a ray casting algorithm. A prelocated matrix takes into account field sizes as well as modifying elements as collimator positions (MLC), blocks, wedges and compensators. Monte Carlo precalculated monoenergetic kernels from 0.1 MeV to 50 MeV were at our disposal. The components of the spectrum were either determined by deconvoluting depth dose curves measured in water or analyzed with a Ge-Li detector system in the case of 60Co. The calculated fluence distribution has to be superposed to the complete kernel containing the spatial energy deposition. Inhomogeneities and tissue interface phenomena (rhoe, Z) have been investigated. The divergence of the rays and the curved surface of the patient are taken into account. Assuming homogenous media, it is possible to shorten the computation time by using the Fast Fourier Transformation (FFT) delivering a first overview within seconds. The algorithm was evaluated and verified under specific conditions of small fields as used in radiosurgery and compared to dose measurements and Monte Carlo calculations. In using both the fast algorithm (FFT) for mainly homogenous conditions on one hand and the very precise superposition for inhomogeneous cases on the other, this algorithm can be a very helpful instrument especially for critical locations in the skull.

Algorithms↗

PubMed1997

[Algorithms in trauma management].

A well-controlled, meticulous process has a far higher probability of resulting in a high quality of medical care than improvization and unstructured creativity. Algorithms display decision-making treatment processes and problem-solving strategies by giving clearly defined and formalized guidelines. The flow chart for decision-making follows the yes/no dichotomy of binary logic. The systematic ordering of decision points and consequent actions is guided by medical priority and thus regulates the time-frame and sequence of each single step in a logical manner. With the help of clinical algorithms highly complex processes such as the management of the severely injured patient can be translated into a clearly structured, logical pathway. Clinical algorithms represent scientifically recognized treatment rules, indicate a solution for solving problems and help users to organize ideas and recognize connections. They delineate a consistent and valid guideline, while allowing deviations in proven exceptions. The use of algorithms allows a systematic search for errors in the process of quality management. In emergency situations they suggest a structured means of problem solving for the less experienced user. Algorithms are useful instruments in the teaching of medical decision-making.

Algorithms↗

PubMed1998

[Spiral CT angiography in diagnosis of acute pulmonary embolism. What factors modify implementation of standard algorithms?].

PURPOSE: Debate about the potential implementation of Spiral-CT in diagnostic algorithms of pulmonary embolism are often focussed on sensitivity and specificity in the context of comparative methodologic studies. We intend to investigate whether additional factors might influence this debate. MATERIALS AND METHODS: On the basis of the current literature and of own experience we study the influence of factors such as availability, acceptance, patient-outcome, and cost effectiveness-studies on the potential implementation of Spiral-CT in diagnostic algorithms of pulmonary embolism. This information is analyzed together with data from comparative methodologic studies. RESULTS: The factors availability, acceptance, patient-outcome, and cost-effectiveness-studies do have substantial influence on the implementation of Spiral-CT in the diagnostic algorithms of pulmonary embolism. Incorporation of these factors into the discussion might lead to more flexible and more patient-oriented algorithms for the diagnosis of pulmonary embolism. CONCLUSION: Availability of equipment, acceptance among clinicians, patient-outcome, and cost-effectiveness evaluations should be implemented into the debate about potential implementation of Spiral-CT in routine diagnostic imaging algorithms of pulmonary embolism.

Acute Disease↗

PubMed2001

A two-dimensional immune algorithm for resolution of overlapping two-way chromatograms.

A two-dimensional immune algorithm is proposed for resolving the multicomponent overlapping two-way data matrices. The method is a development of the one-dimensional immune algorithm proposed elsewhere. When the inner product of vectors is expanded to the similar operation on matrices, the 1D immune algorithm can be expanded to the 2D algorithm which is suitable for the analysis of two-way data matrices. Both simulated and experimental two-way data sets were investigated by the method, and the results prove that the 2D immune algorithm is an effective tool for resolving the overlapping two-way signals. The effect of noise on the recoveries is also discussed.

Algorithms↗

PubMed2003

Optimisation of the OS-EM algorithm and comparison with FBP for image reconstruction on a dual-head camera: a phantom and a clinical 18F-FDG study.

Iterative reconstruction algorithms, such as the ordered subsets expectation maximisation (OS-EM), are a promising alternative to filtered backprojection (FBP). The aims of this study were first to optimise the OS-EM algorithm in terms of iteration number and to study the usefulness of post-filtering, and second to compare OS-EM and FBP for image reconstruction on a fluorine-18 fluorodeoxyglucose ((18)F-FDG) dual-head camera (DHC). These two goals were addressed using phantom acquisitions. The performances of these algorithms were also studied in patient acquisitions performed on a DHC and a PET on the same day. Phantom experiments were performed on a DHC using a Jaszczak phantom containing six spheres filled with (18)F-FDG, two background levels (0.95, 6.80 kBq/ml) and three object contrasts (5.9, 3.7, 2.7). The reconstruction algorithms were FBP with a Gaussian filter (FWHM 0.5-2 pixel width) and OS-EM using 8-128 equivalent iterations (equivalent to the ML-EM algorithm) with and without Gaussian post-filtering [OS-EM (iterations, pixel width)]. Contrast recovery coefficient (CRC) and noise characteristics were assessed. Twenty-two patients (21 male, one female; age 55+/-15 years) with lung cancer underwent, on the same day, PET (1 h post injection of 37 MBq/kg (18)F-FDG) and DHC acquisitions (3 h post injection). DHC data were reconstructed using six methods: FBP (1), OS-EM (16), (40), (40,1), (64) and (64,1). These sets were evaluated by two observers and compared to PET reconstructed with OS-EM (16). The number of detected lesions and the visual quality were assessed. A marked improvement in CRC was observed with OS-EM as compared with FBP when more than 24 iterations were used. The CRC increased markedly from 8 to 40 iterations and then reached a plateau. The noise was stable until 40 iterations and then increased. The best compromise was obtained for OS-EM (32) and OS-EM (40,1). For the patient study, OS-EM provided images of better visual quality, but with no significant difference in detection sensitivity. OS-EM was superior to FBP in terms of contrast recovery and noise level. The optimal compromise between contrast recovery and noise was obtained for OS-EM (32) and (40,1) on the phantom study. The clinical study showed that OS-EM yielded images of better visual quality but with no improvement in terms of detection of lung cancer.

Algorithms↗

PubMed2006

A hybrid algorithm for PET/CT image merger in hybrid scanners.

PURPOSE: To improve the PET image quality of a hybrid PET/CT scanner by merging CT borders with PET texture. PET/CT scanners provide both high-resolution CT images showing anatomical details and PET images of low-resolution physiological information about radiopharmaceutical uptake. Standard smoothing of noisy PET images may further impair PET resolution, reducing small lesion detectability. METHODS: The CT edge data and the PET texture data were merged using a modified form of an algorithm called HCT (hybrid computed tomography). In merged PET/CT images, each PET pixel value was estimated by iteratively applying a corrected 2D Taylor expansion to each of its eight neighbors. The spatial derivative term was used only near anatomical edges provided by the CT. This counts-preserving algorithm was tested on a special resolution phantom and patient data sets obtained by PET/CT acquisitions. RESULTS: The HCT algorithm provided phantom PET images with sharp borders and improved resolution (< or = 3 mm as compared to > or = 4 mm). HCT increased the signal to background contrast ratios by an average of 61% (40-89%) while maintaining noise reduction similar to the Gaussian filtering standard in PET. In the clinical PET images, HCT allowed for an improved delineation of pulmonary and pelvic lesions and an improved visualization of the brain. CONCLUSION: A new reconstruction algorithm for merging CT anatomical edge data with functional PET data has been introduced. The algorithm smooths noisy PET images while retaining sharper edges at corresponding anatomical borders, resulting in an improvement in resolution and contrast ratio.

Algorithms↗

PubMed2002

[Histological diagnosis of inflammatory skin diseases. Use of a simple algorithm and modern diagnostic methods].

The histological diagnosis of inflammatory skin diseases on a day-to-day routine basis poses the difficult task to characterise a dynamic clinical process by histomorphological analysis of one single lesion. Very complex algorithms which are meant to lead to the correct diagnosis are difficult to use. To facilitate the process and reduce the number of algorithms the following method is proposed: 1. Histological examination under low power Definition of lesions altered by scratching 2. Localisation of the significant pathological alterations as follows: Changes in epidermis and dermis Blister formation Changes in dermis/subcutis without characteristic changes in the epidermis Changes mainly in the subcutis 3. Closer examination using a simple algorithm and planning of further investigations following defined criteria: In the case of changes in epidermis and dermis definition of spongiotic, psoriasiform or lichenoid dermatitis (Abb. 1). In the case of blister formation definition of the blister following the given algorithm (Abb. 1). In the case of changes in dermis/subcutis without characteristic changes in the epidermis after exclusion of vasculitis and lymphoma definition of the main pattern as lymphocytic, neutrophilic, eosinophilic, lymphoplasmocytic or granulomatous and following the given algorithm (Abb. 2). In the case of changes mainly in the subcutis after exclusion of vasculitis and lymphoma definition of the main pattern of panniculitis as septal or/and lobular (Abb. 2). Exclusion of PAS positive microorganisms and checking if the general pattern fits into infectious correlation. Use of clinicopathological correlation.

Algorithms↗

PubMed2005

Global left ventricular function in cardiac CT. Evaluation of an automated 3D region-growing segmentation algorithm.

The purpose was to evaluate a new semi-automated 3D region-growing segmentation algorithm for functional analysis of the left ventricle in multislice CT (MSCT) of the heart. Twenty patients underwent contrast-enhanced MSCT of the heart (collimation 16 x 0.75 mm; 120 kV; 550 mAseff). Multiphase image reconstructions with 1-mm axial slices and 8-mm short-axis slices were performed. Left ventricular volume measurements (end-diastolic volume, end-systolic volume, ejection fraction and stroke volume) from manually drawn endocardial contours in the short axis slices were compared to semi-automated region-growing segmentation of the left ventricle from the 1-mm axial slices. The post-processing-time for both methods was recorded. Applying the new region-growing algorithm in 13/20 patients (65%), proper segmentation of the left ventricle was feasible. In these patients, the signal-to-noise ratio was higher than in the remaining patients (3.2+/-1.0 vs. 2.6+/-0.6). Volume measurements of both segmentation algorithms showed an excellent correlation (all P<or=0.0001); the limits of agreement for the ejection fraction were 2.3+/-8.3 ml. In the patients with proper segmentation the mean post-processing time using the region-growing algorithm was diminished by 44.2%. On the basis of a good contrast-enhanced data set, a left ventricular volume analysis using the new semi-automated region-growing segmentation algorithm is technically feasible, accurate and more time-effective.

Aged↗

PubMed2005

A randomised study on a new cost-effective algorithm of quick intraoperative intact parathyroid hormone assay in secondary hyperparathyroidism.

BACKGROUND AND AIMS: The use of intraoperative intact parathyroid hormone (iPTH) assay in secondary renal hyperparathyroidism (SHP) has been limited by the relatively low cost effectiveness of the assay in improving the success rate for primary bilateral neck exploration. The study aimed at determining, in a prospective, randomised trial, the cost effectiveness and impact of the routine employment of a "six-sample" versus "two-sample" algorithm of the intraoperative iPTH assay during surgery for SHP on intraoperative decision making and surgical success rate. PATIENTS AND METHODS: One hundred and two consecutive patients with severe SHP and qualified for subtotal parathyroidectomy were randomly allocated to two equal-sized groups: group A, in which the intraoperative iPTH serum level was determined in six consecutive samples: preoperative, pre-excision, 5, 10, 20 and 60 min, and group B, in which the intraoperative iPTH serum level was determined twice only: preoperatively and 10 min. The STAT intraoperative intact-PTH immunoassay was employed. In group B, in patients with serum iPTH decrease lower than 60% of the baseline at 10 min, an additional measurement was performed at 20-min post-excision. If a decrease of 80% or more of the baseline was not obtained, the exploration was extended in search of remaining hyperfunctioning parathyroid tissue. RESULTS: The surgical success rate was 96.1% and 98.0% (in group A and B, respectively). The impact of the intraoperative iPTH assay on surgical decision making was demonstrated in 13.7% and 15.7% (in group A and B, respectively). The assay was helpful in identifying patients with supranumerary hyperfunctioning parathyroid tissue (5.9% vs 7.8% in group A and B, respectively), patients with fewer than four parathyroid glands (3.9% vs 5.9% in group A and B, respectively) and patients with remaining hyperfunctioning parathyroid tissue suspected to be located within the mediastinum in cases of negative bilateral neck exploration who benefit from transcervical thymectomy. The diagnostic accuracy of the intraoperative iPTH assay was 100% in both groups. The accuracy of two-sample algorithm increased from 96% to 100% if an additional serum iPTH determination was performed in borderline cases with an iPTH drop lower than 60% of the baseline at 10 min. The cost-effectiveness analysis showed significant savings in group B, equal to Euro 87.6 per patient, with the unchanged diagnostic accuracy of the two-sample algorithm. CONCLUSIONS: The intraoperative iPTH assay in patients operated on for secondary hyperparathyroidism offers support in surgical decision making in the majority of patients, allowing for correct identification of patients with supranumerary ectopic hyperfunctioning parathyroid glands, and in patients with fewer than four parathyroid glands. It also correctly identifies patients who do not benefit from blind thymectomy. The two-sample algorithm, extended to include three determinations in selected cases, has the same 100% diagnostic accuracy as the six-sample algorithm, the former being a much more cost-effective procedure.

Adult↗

PubMed1998

An algorithm for selection of instrumentation levels in scoliosis.

Appropriate levels for instrumentation and fusion in scoliosis have been a matter of debate among surgeons since the introduction of operative management of this deformity. We set out to examine the hypothesis that the amount of correction achieved in all planes during surgical instrumentation of a curve should be less than, or comparable to, the degree of correction attainable at any non-instrumented adjacent curve. An algorithm was designed to facilitate preoperative planning and intraoperative performance of spinal fusion procedures in the management of scoliosis. To test the validity of the hypothesis and the proposed algorithm, measurements were taken from the preoperative radiographs of 200 patients. The dimensions of the curves were obtained from an initial set of four X-ray films: (1) standing anteroposterior film of the whole spine, (2) standing lateral film of the whole spine, (3) two properly performed side-bending films including each curve of the spine. With this data, a plan was designed using the algorithm. The results of this plan were compared with the actual results of the surgery, which were revealed only at this stage. All patients in whom actual instrumentation levels fell within those predicted by the proposed algorithm had no imbalance at follow-up. All patients whose actual instrumentation levels were short of those recommended by the algorithm showed obvious imbalance on final postoperative standing radiograph.

Adolescent↗

PubMed2006

An algorithm for model construction and its applications to pharmacogenomic studies.

A model depicts the relationship between clinical phenotypes and genotypes on a set of genetic polymorphisms. After the model is constructed and validated, it may be used to predict clinical phenotypes such as traits of complex diseases. A pharmacogenomic model is used to predict the efficacies or adverse drug reactions of a medication. The construction of a model is a challenging task. This is because a single-locus polymorphism does not contain enough information to stratify patients in general, given the complex biological mechanisms involved. An exhaustive search for the correct combination of genotypes across multiple loci is, however, computationally infeasible. We are, thus, motivated to propose a novel algorithm for the construction of models using the multiple single-nucleotide polymorphism (SNP) information in diplotype forms. This algorithm utilizes the techniques of genetic algorithms and Boolean algebra (GABA). The proposed algorithm is tested on simulated data, as well as real genotype datasets of chronic hepatitis C patients treated with interferon-combined therapy. A model for predicting the treatment efficacy is constructed and validated. The results showed that the proposed algorithm is very effective in deriving models comprising multiple SNPs.

Algorithms↗

PubMedDate not supplied

Comparison of commercially available genetic algorithms: gas as variable selection tool.

Many commercially available software programs claim similar efficiency and accuracy as variable selection tools. Genetic algorithms are commonly used variable selection methods where most relevant variables can be differentiated from 'less important' variables using evolutionary computing techniques. However, different vendors offer several algorithms, and the puzzling question is: which one is the appropriate method of choice? In this study, several genetic algorithm tools (e.g. GFA from Cerius2, QuaSAR-Evolution from MOE and Partek's genetic algorithm) were compared. Stepwise multiple linear regression models were generated using the most relevant variables identified by the above genetic algorithms. This procedure led to the successful generation of Quantitative Structure activity Relationship (QSAR) models for (a) proprietary datasets and (b) the Selwood dataset.

Algorithms↗

PubMed2005

Non-linear cancer classification using a modified radial basis function classification algorithm.

This paper proposes a modified radial basis function classification algorithm for non-linear cancer classification. In the algorithm, a modified simulated annealing method is developed and combined with the linear least square and gradient paradigms to optimize the structure of the radial basis function (RBF) classifier. The proposed algorithm can be adopted to perform non-linear cancer classification based on gene expression profiles and applied to two microarray data sets involving various human tumor classes: (1) Normal versus colon tumor; (2) acute myeloid leukemia (AML) versus acute lymphoblastic leukemia (ALL). Finally, accuracy and stability for the proposed algorithm are further demonstrated by comparing with the other cancer classification algorithms.

Acute Disease↗

PubMed1986

Parallel algorithms for the analysis of two-dimensional electrophoresis gels.

This paper describes some parallel processing algorithms for the analysis of two-dimensional electrophoresis images. The machine used for the processing was the CLIP4 Cellular Array Computer at University College, London, one of the largest processor arrays in the world. Included in this paper are an algorithm for centroid detection, Gaussian fitting algorithms, and an algorithm for the extraction of data out of the cellular array machine. It is shown that these parallel algorithms can run at a speed almost completely independent of the number of spots in the gel images.

Algorithms↗

PubMed1995

Neuromagnetic source imaging with FOCUSS: a recursive weighted minimum norm algorithm.

The paper describes a new algorithm for tomographic source reconstruction in neural electromagnetic inverse problems. Termed FOCUSS (FOCal Underdetermined System Solution), this algorithm combines the desired features of the two major approaches to electromagnetic inverse procedures. Like multiple current dipole modeling methods, FOCUSS produces high resolution solutions appropriate for the highly localized sources often encountered in electromagnetic imaging. Like linear estimation methods, FOCUSS allows current sources to assume arbitrary shapes and it preserves the generality and ease of application characteristic of this group of methods. It stands apart from standard signal processing techniques because, as an initialization-dependent algorithm, it accommodates the non-unique set of feasible solutions that arise from the neuroelectric source constraints. FOCUSS is based on recursive, weighted norm minimization. The consequence of the repeated weighting procedure is, in effect, to concentrate the solution in the minimal active regions that are essential for accurately reproducing the measurements. The FOCUSS algorithm is introduced and its properties are illustrated in the context of a number of simulations, first using exact measurements in 2- and 3-D problems, and then in the presence of noise and modeling errors. The results suggest that FOCUSS is a powerful algorithm with considerable utility for tomographic current estimation.

Algorithms↗

PubMed1995

An expectation maximization reconstruction algorithm for emission tomography with non-uniform entropy prior.

A Bayesian image reconstruction algorithm is proposed for emission tomography. It incorporates the Poisson nature of the noise in the projection data and uses a non-uniform entropy as an a priori probability distribution of the image in a maximum a posteriori (MAP) approach. The expectation maximization (EM) method was applied to find the MAP estimator. The Newton-Raphson numerical method whose convergence and positive solutions are proven, was used to solve the EM problem. The prior mean at iteration k was determined by smoothing the image obtained at iteration k-1. Comparisons between the ML and the MAP algorithm were carried out with a numerical phantom that contains a narrow valley region. The ML solution after 50 iterations was chosen as the initial solution for the MAP algorithm, since the global performance of the ML algorithm deteriorates with increasing number of iterations while its local performance in the valley region is always improving. The resulting algorithm is a compromise between ML who has the best local performance in the valley region and the MAP who has the best global performance.

Algorithms↗