Biomedical subjects

Yongjie Li

Publications and source records attributed to Yongjie Li.

7 recordsLinked to original sources

PubMed2005

A particle swarm optimization algorithm for beam angle selection in intensity-modulated radiotherapy planning.

Automatic beam angle selection is an important but challenging problem for intensity-modulated radiation therapy (IMRT) planning. Though many efforts have been made, it is still not very satisfactory in clinical IMRT practice because of overextensive computation of the inverse problem. In this paper, a new technique named BASPSO (Beam Angle Selection with a Particle Swarm Optimization algorithm) is presented to improve the efficiency of the beam angle optimization problem. Originally developed as a tool for simulating social behaviour, the particle swarm optimization (PSO) algorithm is a relatively new population-based evolutionary optimization technique first introduced by Kennedy and Eberhart in 1995. In the proposed BASPSO, the beam angles are optimized using PSO by treating each beam configuration as a particle (individual), and the beam intensity maps for each beam configuration are optimized using the conjugate gradient (CG) algorithm. These two optimization processes are implemented iteratively. The performance of each individual is evaluated by a fitness value calculated with a physical objective function. A population of these individuals is evolved by cooperation and competition among the individuals themselves through generations. The optimization results of a simulated case with known optimal beam angles and two clinical cases (a prostate case and a head-and-neck case) show that PSO is valid and efficient and can speed up the beam angle optimization process. Furthermore, the performance comparisons based on the preliminary results indicate that, as a whole, the PSO-based algorithm seems to outperform, or at least compete with, the GA-based algorithm in computation time and robustness. In conclusion, the reported work suggested that the introduced PSO algorithm could act as a new promising solution to the beam angle optimization problem and potentially other optimization problems in IMRT, though further studies need to be investigated.

Algorithms↗

PubMed2004

Automatic beam angle selection in IMRT planning using genetic algorithm.

The selection of suitable beam angles in external beam radiotherapy is at present generally based upon the experience of the human planner. The requirement to automatically select beam angles is particularly highlighted in intensity-modulated radiation therapy (IMRT), in which a smaller number of modulated beams is hoped to be used, in comparison with conformal radiotherapy. It has been proved by many researchers that the selection of suitable beam angles is most valuable for a plan with a small number of beams (< or = 5). In this paper an efficient method is presented to investigate how to improve the dose distributions by selecting suitable coplanar beam angles. In our automatic beam angle selection (ABAS) algorithm, the optimal coplanar beam angles correspond to the lowest objective function value of the dose distributions calculated using the intensity-modulated maps of this group of candidate beams. Due to the complexity of the problem and the large search space involved, the selection of beam angles and the optimization of intensity maps are treated as two separate processes and implemented iteratively. A genetic algorithm (GA) incorporated with an immunity operation is used to select suitable beam angles, and a conjugate gradient (CG) method is used to quickly optimize intensity maps for each selected beam combination based on a dose-based objective function. A pencil-beam-based three-dimensional (3D) full scatter convolution (FSC) algorithm is employed for the dose calculation. Two simulated cases with obvious optimal beam angles are used to verify the validity of the presented technique, and a more complicated case simulating a prostate tumour and two clinical cases are employed to test the efficiency of ABAS. The results show that ABAS is valid and efficient and can improve the dose distributions within a clinically acceptable computation time.

Algorithms↗

PubMed2004

Neuronal activity in the basal ganglia and thalamus in patients with dystonia.

OBJECTIVE: To explore the role of abnormal neuronal activity in the basal ganglia and thalamus in the generation of dystonia. METHODS: Microelectrode recording was performed in the globus pallidus internus (GPi), ventral thalamic nuclear group ventral oral posterior/ventral intermediate, Vop/Vim) and subthalamic nucleus (STN) in patients with primary dystonia (n=11) or secondary dystonia (n=9) during surgery. Electromyogram (EMG) was simultaneously recorded in selected muscle groups. Single unit analysis and cross-correlations were carried out. RESULTS: Three hundred and sixty-seven neurons were obtained from 29 trajectories (GPi: 13; Vop/Vim: 12; STN: 4), 87% exhibited altered neuronal activity including grouped discharges in GPi (n=79) and STN (n=37), long-lasting neuronal activity (n=70) and rapid neuronal discharge (n=86) in Vop/Vim. There were neurons in Vop, GPi and STN firing at the same frequency as EMG during dystonia (mean: 0.39 Hz, range 0.12-0.84 Hz). Significant correlations between neuronal activity and EMG at the frequency of dystonia were obtained (GPi: r2=0.7 (n=31), Vop/Vim: r2=0.64 (n=18) and STN: r2=0.86 (n=17)). CONCLUSIONS: Consistent with previous findings of abnormalities observed in Vop/VIM and GPi in relation to dystonia, the present data further show that the altered activity in GPi, specifically in dorsal subregions of GPi, Vop/Vim and STN is likely to be directly involved in the production of dystonic movement. Dystonia-related neuronal activity observed in motor thalamus and basal ganglia nuclei of GPi and STN indicates a critical role of their interactions affecting both indirect and direct pathways in the development of either generalized or focal dystonia. SIGNIFICANCE: These data support a central role of the basal ganglia in producing dystonic movements.

Adolescent↗

PubMed2003

Genetic algorithm based deliverable segments optimization for static intensity-modulated radiotherapy.

The static delivery technique (also called step-and-shoot technique) has been widely used in intensity-modulated radiotherapy (IMRT) because of the simple delivery and easy quality assurance. Conventional static IMRT consists of two steps: first to calculate the intensity-modulated beam profiles using an inverse planning algorithm, and then to translate these profiles into a series of uniform segments using a leaf-sequencing tool. In order to simplify the procedure and shorten the treatment time of the static mode, an efficient technique, called genetic algorithm based deliverable segments optimization (GADSO), is developed in our work, which combines these two steps into one. Taking the pre-defined beams and the total number of segments per treatment as input, the number of segments for each beam, the segment shapes and weights are determined automatically. A group of interim modulated beam profiles quickly calculated using a conjugate gradient (CG) method are used to determine the segment number for each beam and to initialize segment shapes. A modified genetic algorithm based on a two-dimensional binary coding scheme is used to optimize the segment shapes, and a CG method is used to optimize the segment weights. The physical characters of a multileaf collimator, such as the leaves interdigitation limitation and leaves maximum over-travel distance, are incorporated into the optimization. The algorithm is applied to some examples and the results demonstrate that GADSO is able to produce highly conformal dose distributions using 20-30 deliverable segments per treatment within a clinically acceptable computation time.

Adult↗

PubMed2003

Determination of fatty acid levels in erythrocyte membranes of patients with chronic fatigue syndrome.

Chronic fatigue syndrome (CFS) is an illness characterized by persistent and relapsing fatigue, often accompanied by numerous symptoms involving various systems of whole body. The etiology of CFS remains unclear. Literature reported whether the concentrations of the essential fatty acids in red cell membranes of CFS patients were decreased is controversial. In our study, Forty-two patients who fulfilled the diagnostic criteria defined by Centers for Disease Control and Prevention (CDC). Thirty-seven age- and sex-matched controls were selected from healthy medical staffs and volunteers. After lipid analysis, we found that the levels of the arachidonic acid (ARA) and docosahexanoic acid (DHA) were decreased in patients suffered from CFS. However, the levels of the palmitic acid and oleic acid were increased. We speculated that there are two possible mechanisms--one of which is that oxidative stress has led to an excessive oxidation and resulting in the above fatty acids. Alternatively, insufficiency of ingestion of fatty acids might not be the major cause.

Adult↗

PubMed2002

[Quantitative assessment of Parkinsonian rigidity by vessel Doppler ultrasonography].

OBJECTIVE: To investigate the value of quantitative assessment of parkinsonian rigidity by vessel Doppler ultrasonography. METHODS: The diameter of the rigid limbs, including radial artery and vein, ulnar artery and vein, brachial veins, popliteal vein, anterior tibial vein, and posterior tibial vein in twelve individuals with PD and twelve age matched controls were measured by ultrasonography in both "on" and "off" states. Meanwhile the UPDRS unified Parkinson's disease rating scale for rigidity were also recorded both in "on" and "off " states by experienced neurologists. RESULTS: The mean diameter of radial vein, ulnar vein, brachial vein, popliteal vein, anterior tibial vein and posterior tibial vein, were 1.14, 1.13, 2.47, 3.85, 1.89, and 1.33 mm respectively in "off " state (group "A"), and were 1.58, 1.54, 2.88, 4.65, 2.27, and 1.69 mm respectively in "on" states (group "B") among the PD patients. The diameters of corresponding vessels in the controls (group "C") were 2.07, 1.69, 4.15, 5.07, 2.63, and 1.99 mm respectively. The data increased from group "A" to "C" gradually. Paired samples t tested showed a significant difference between the data of group A and group B (P = 0.00 approximately 0.03) and between group A and group C (P = 0.00 approximately 0.02) and no significant difference between group B and group C (P > 0.05, except for brachial vein with P = 0.02). The data of vein diameters in rigid limbs were correspondent to the UPDRS scores for rigidity with the correlation coefficient of 0.71, 0.82, 0.91, 0.73 (all P < 0.01), 0.60 P < 0.05 , and 0.77 P < 0.01) for the above mentioned vessels respectively. CONCLUSION: The diameter of distant veins in limbs can be adopted as objective and quantitative indicators for parkinsonian rigidity and contribute to the evaluation of therapeutical effects.

Aged↗

PubMed2002

[Relationship between the heterotopic neurons and intractable epilepsy].

OBJECTIVE: To discuss the relationship between heterotopic neurons and intractable epilepsy. METHODS: Epileptogenic zones were precisely located with MRI, video-EEG monitoring, intracranial electrical recording and electrocorticography monitoring and then resected in seven patients. The removed tissue was processed for conventional pathological examination with immunohistochemical staining. RESULTS: Heterotopic neurons were found in the white matter of the specimens. All the seven cases experienced a favorable outcome, with six seizure free. CONCLUSION: The heterotopic neurons scattered or clustered in the white matter contribute to the pathogenesis of intractable epilepsy.

Adolescent↗