Thoracic Geometry Research Articles

Syndrome Sinistre: Left Brachiocephalic Vein Compression and its Neurological Manifestations.

Embryologically, the left brachiocephalic vein (LBV) originates as an anastomotic channel between the right and left anterior cardinal veins. This positions the LBV between the manubrium sterni anteriorly and the innominate artery posteriorly. This pattern of adjacency of the aorta to the LBV is unique to mammals and results from a quirk of evolution. With age, the ascending aorta unfolds, elongates and dilates. Simultaneously, there is a change in the thoracic geometry that reduces the thoracic volume primarily from disc height loss and kyphosis. These transitions progressively compress the LBV. Normally, this compression is circumvented via collateral pathways and "Blood finds a way". However, traversing these circuitous pathways comes at a cost and can result in delayed transit times and venous congestion. While it is possible that compression of the LBV in the setting of adequate collateral channels may fail to provoke any pathologic sequelae, we propose a phenomenon in which such compression in the setting of inadequate collateral circulation may lead to a state of pathologic venous congestion. This anatomic anomaly and its associated clinical features, if identified, can offer a new avenue for treatment options for some of the hitherto unexplained neurologic disorders.

The Effects of Conservative Treatment on Geometric Morphology of the Spine and Thoracic Cage in Patients with Adolescent Idiopathic Scoliosis: A 1-Year Follow-up

ABSTRACT Introduction The thoracic cage has a direct relation with the spine and thereby scoliosis affects spinal morphology. The aim of the study is to investigate the effects of a 1-year conservative treatment on the geometric morphology of the spine and thoracic cage in patients with adolescent idiopathic scoliosis (AIS). Methods Thirty-six patients with AIS were assessed retrospectively for the initiation of conservative treatment and at 1-year follow-up. Patients were divided into two groups based on the intervention method: exercises-only group (ExG) and brace plus exercises group (BrG). The posteroanterior and lateral radiograph of each patient were measured in terms of spinal morphology including coronal, sagittal, transverse spinal, and thoracic cage parameters. Besides, the success rate of the conservative treatment was recorded by the sum of the stabilization and correction of each patient. Results No significant difference was found in the thoracic dimensions, thoracic geometry, and coronal and transverse plane parameters in ExG group (P > 0.05). The spine height increased (P = 0.006), whereas other parameters did not change (P > 0.05) in BrG. Lumbar lordosis decreased in ExG group (P = 0.025). The total success rate of the conservative treatment in AIS patients was 75%. The success rate of ExG and BrG was 68.4% and 82.4%, respectively. Conclusions The conservative treatment including both bracing and exercise seems to provide an additional elongation over the spine height without causing a negative effect in the spine and thoracic cage geometry in AIS. Clinical Relevance Bracing and exercise treatment do not have a negative impact on thoracic cage geometry in AIS.

Impact of Thoracic Cage Dimension and Geometry on Cardiopulmonary Function in Patients With Congenital Scoliosis: A Prospective Study.

A prospective study of cardiopulmonary function in patients with congenital scoliosis (CS). To investigate the relationship of thoracic cage deformity and exercise tolerance in CS patients. Congenital thoracic scoliosis and chest deformity lead to restrictive pulmonary dysfunction and in some severe cases cause cardiopulmonary failure. However, it is still unknown the relationship between thoracic deformity and exercise performance. Patients with congenital thoracic spinal deformity were included and had radiological assessment of thoracic cage, pulmonary function testing, and cardiopulmonary exercise testing. Thoracic dimension including height, width, and depth were measured and geometry parameters were calculated. Two-tailed Pearson and Spearman correlation test and linear regression analysis were performed to investigate correlation of radiographic parameters, pulmonary function, and physical capacity. Sixty patients (41 females and 19 males) were included, with an average age of 18.9 years. Patients with smaller thoracic height (P < 0.001) and width (P < 0.01) and larger depth (P < 0.05) had significantly worse static pulmonary function. In exercise testing, these patients showed significant tendency of ventilation insufficiency, including lower minute ventilation (P < 0.05), faster breathing frequency (P < 0.05), and smaller tidal volume (P < 0.01). Thoracic depth was negatively correlated to exercise capacity, reflected by work rate (P < 0.001), peak oxygen intake (P < 0.001), and heart rate (P = 0.043). Patients with abnormal thoracic geometry, especially a lower ratio of height to depth and a lower ratio of width to depth, have significantly worse static pulmonary function and exercise capacity (all P < 0.05). Decreasing thoracic height and width results in restrictive pulmonary dysfunction. Distortion and asymmetry of the thoracic cage are associated with abnormal breathing pattern and reduction of exercise capacity. 3.

ECG Electrode Placements for Magnetohydrodynamic Voltage Suppression

This study aims to investigate a set of electrocardiogram (ECG) electrode lead locations to improve the quality of four-lead ECG signals acquired during magnetic resonance imaging (MRI). This was achieved by identifying electrode placements that minimized the amount of induced magnetohydrodynamic voltages (VMHD) in the ECG signals. Reducing VMHD can improve the accuracy of QRS complex detection in ECG as well as heartbeat synchronization between MRI and ECG during the acquisition of cardiac cine. A vector model based on thoracic geometry was developed to predict induced VMHD and to optimize four-lead ECG electrode placement for the purposes of improved MRI gating. Four human subjects were recruited for vector model establishment (Group 1), and five human subjects were recruited for validation of VMHD reduction in the proposed four-lead ECG (Group 2). The vector model was established using 12-lead ECG data recorded from Group 1 of four healthy subjects at 3 Tesla, and a gradient descent optimization routine was utilized to predict optimal four-lead ECG placement based on VMHD vector alignment. The optimized four-lead ECG was then validated in Group 2 of five healthy subjects by comparing the standard and proposed lead placements. A 43.41% reduction in VMHD was observed in ECGs using the proposed electrode placement, and the QRS complex was preserved. A VMHD-minimized electrode placement for four-lead ECG gating was presented and shown to reduce induced magnetohydrodynamic (MHD) signals, potentially allowing for improved cardiac MRI physiological monitoring.

Left ventricular orientation and position in an advanced heart failure population

IntroductionPrevious canine and in silico studies indicate that left ventricular (LV) orientation and position have clinically significant effects on standard ECG elements, which are particularly relevant in an advanced heart failure (HF) population. Our objectives were to investigate the real-world implications of these previous results by describing for the first time the range of LV orientations and positions in HF patients, identifying clinical predictors of orientation and position, and investigating how thoracic geometry may affect orientation and position. Materials and methodsCardiac MRIs were used to measure LV orientation angles, LV position, chest dimensions, and the ratio of LV volume to thoracic area (LVTR). Multivariate regression analyses were used to identify significant predictors of orientation and position. ResultsThe mean frontal plane LV orientation angle was 31 ± 11° (range, 0°–47°) and fell within the ranges used in previous studies of orientation effects. Orientation in the transverse plane, the effects of which have not been simulated, averaged 48 ± 10° (range, 21°–71°). The ranges of LV positions in the frontal and transverse planes (7.9 and 5.6 cm, respectively) are similar to or greater than those used in silico. Orientation and position were weakly correlated with multiple significant predictors, and the relationship between HF progression and LV orientation and position could not be determined. ConclusionVariation in LV orientation and position in advanced HF patients is large and cannot be readily predicted using the standard clinical variables or additional thoracic geometry measures used in this study. These findings may have significant clinical implications because of the possible effects of orientation and position on key ECG features. New tools and additional studies are needed before LV orientation or position data can be incorporated into clinical ECG interpretation.

Age-related changes in thoracic skeletal geometry of elderly females

ABSTRACTObjective: Both females and the elderly have been identified as vulnerable populations with increased injury and mortality risk in multiple crash scenarios. Particularly in frontal impacts, older females show higher risk to the chest and thorax than their younger or male counterparts. Thoracic geometry plays a role in this increase, and this study aims to quantify key parts of that geometry in a way that can directly inform human body models that incorporate the concept of person age.Methods: Computed tomography scans from 2 female subject groups aged 20–35 and 65–99 were selected from the International Center for Automotive Medicine scan database representing young and old female populations. A model of thoracic skeletal anatomy was built for each subject from independent parametric models of the spine, ribs, and sternum, along with further parametric models of those components’ spatial relationships. Parameter values between the 2 groups are directly compared, and average parameter values within each group are used to generate statistically average skeletal geometry for young and old females. In addition to the anatomic measures explicitly used in the parameterization scheme, key measures of rib cage depth and spine curvature are taken from both the underlying subject pool and from the resultant representative geometries.Results: Statistically significant differences were seen between the young and old groups’ spine and rib anatomic components, with no significant differences in local sternal geometry found. Vertebral segments in older females had higher angles relative to their inferior neighbors, providing a quantification of the kyphotic curvature known to be associated with age. Ribs in older females had greater end-to-end span, greater aspect ratio, and reduced out-of-plane deviation, producing an elongated and overall flatter curvature that leads to distal rib ends extending further anteriorly in older individuals. Combined differences in spine curvature and rib geometry led to an 18-mm difference in anterior placement of the sternum between young and old subjects.Conclusions: This study provides new geometric data regarding the variability in anthropometry of adult females with age and has utility in advancing the veracity of current human body models. A simplified scaffold representation of underlying 3-dimensional bones within the thorax is presented, and the reported young and old female parameter sets can be used to characterize the anatomic differences expected with age and to both validate and drive morphing algorithms for aged human body models. The modular approach taken allows model parameters to hold inherent and intuitive meaning, offering advantages over more generalized methods such as principal component analysis. Geometry can be assessed on a component level or a whole thorax level, and the parametric representation of thorax shape allows direct comparisons between the current study and other individuals or human body models.

An anthropomorphic breathing phantom of the thorax for testing new motion mitigation techniques for pencil beam scanning proton therapy

Motion-induced range changes and incorrectly placed dose spots strongly affect the quality of pencil-beam-scanned (PBS) proton therapy, especially in thoracic tumour sites, where density changes are large. Thus motion-mitigation techniques are necessary, which must be validated in a realistic patient-like geometry. We report on the development and characterisation of a dynamic, anthropomorphic, thorax phantom that can realistically mimic thoracic motions and anatomical features for verifications of proton and photon 4D treatments.The presented phantom is of an average thorax size, and consists of inflatable, deformable lungs surrounded by a skeleton and skin. A mobile ‘tumour’ is embedded in the lungs in which dosimetry devices (such as radiochromic films) can be inserted. Motion of the tumour and deformation of the thorax is controlled via a custom made pump system driving air into and out of the lungs. Comprehensive commissioning tests have been performed to evaluate the mechanical performance of the phantom, its visibility on CT and MR imaging and its feasibility for dosimetric validation of 4D proton treatments.The phantom performed well on both regular and irregular pre-programmed breathing curves, reaching peak-to-peak amplitudes in the tumour of <20 mm. Some hysteresis in the inflation versus deflation phases was seen. All materials were clearly visualised in CT scans, and all, except the bone and lung components, were MRI visible. Radiochromic film measurements in the phantom showed that imaging for repositioning was required (as for a patient treatment). Dosimetry was feasible with Gamma Index agreements (4%/4 mm) between film dose and planned dose >90% in the central planes of the target.The results of this study demonstrate that this anthropomorphic thorax phantom is suitable for imaging and dosimetric studies in a thoracic geometry closely-matched to lung cancer patients under realistic motion conditions.

Quantification of motion of the thoracic aorta after ascending aortic repair of type-A dissection.

To quantify cardiac and respiratory deformations of the thoracic aorta after ascending aortic graft repair. Eight patients were scanned with cardiac-resolved computed tomography angiography during inspiratory/expiratory breath-holds. Aortic centerlines and lumen were extracted to compute the arclength, curvature, angulation, and cross-section shape. From systole to diastole, the angle of graft[Formula: see text]arch increased by 2.4[Formula: see text] ± 1.8[Formula: see text] (P < 0.01) and the angle of arch[Formula: see text]descending aorta decreased by 2.4[Formula: see text] ± 2.6[Formula: see text] (P < 0.05), while the effective diameter of the proximal arch decreased by 2.4 ± 1.9% (P < 0.01), a greater change than those of the graft or distal arch (P < 0.05). From inspiration to expiration, the angle of graft[Formula: see text]arch increased by 2.8[Formula: see text] ± 2.6[Formula: see text] (P < 0.02) with the peak curvature increase (P < 0.05). Shorter graft length was correlated with greater cardiac-induced graft[Formula: see text]arch angulation, and longer graft length was correlated with greater respiratory-induced arch [Formula: see text] descending aorta angulation (R [Formula: see text] 0.50). The thoracic aorta changed curvature and angulation with cardiac and respiratory influences, driven by aortic root and arch motion. The thoracic aortic geometry and deformation are correlated with the ascending aortic graft length.

A method to adapt thoracic impedance based on chest geometry and composition to assess congestion in heart failure patients

Multi-frequency trans-thoracic bioimpedance (TTI) could be used to track fluid changes and congestion of the lungs, however, patient specific characteristics may impact the measurements. We investigated the effects of thoracic geometry and composition on measurements of TTI and developed an equation to calculate a personalized fluid index. Simulations of TTI measurements for varying levels of chest circumference, fat and muscle proportion were used to derive parameters for a model predicting expected values of TTI. This model was then adapted to measurements from a control group of 36 healthy volunteers to predict TTI and lung fluids (fluid index). Twenty heart failure (HF) patients treated for acute HF were then used to compare the changes in the personalized fluid index to symptoms of HF and predicted TTI to measurements at hospital discharge. All the derived body characteristics affected the TTI measurements in healthy volunteers and together the model predicted the measured TTI with 8.9% mean absolute error. In HF patients the estimated TTI correlated well with the discharged TTI (r=0.73,p <0.001) and the personalized fluid index followed changes in symptom levels during treatment. However, 37% (n=7) of the patients were discharged well below the model expected value. Accounting for chest geometry and composition might help in interpreting TTI measurements.

Age- and Sex-Specific Thorax Finite Element Model Development and Simulation

Objective: The shape, size, bone density, and cortical thickness of the thoracic skeleton vary significantly with age and sex, which can affect the injury tolerance, especially in at-risk populations such as the elderly. Computational modeling has emerged as a powerful and versatile tool to assess injury risk. However, current computational models only represent certain ages and sexes in the population. The purpose of this study was to morph an existing finite element (FE) model of the thorax to depict thorax morphology for males and females of ages 30 and 70 years old (YO) and to investigate the effect on injury risk.Methods: Age- and sex-specific FE models were developed using thin-plate spline interpolation. In order to execute the thin-plate spline interpolation, homologous landmarks on the reference, target, and FE model are required. An image segmentation and registration algorithm was used to collect homologous rib and sternum landmark data from males and females aged 0–100 years. The Generalized Procrustes Analysis was applied to the homologous landmark data to quantify age- and sex-specific isolated shape changes in the thorax. The Global Human Body Models Consortium (GHBMC) 50th percentile male occupant model was morphed to create age- and sex-specific thoracic shape change models (scaled to a 50th percentile male size). To evaluate the thoracic response, 2 loading cases (frontal hub impact and lateral impact) were simulated to assess the importance of geometric and material property changes with age and sex.Results: Due to the geometric and material property changes with age and sex, there were observed differences in the response of the thorax in both the frontal and lateral impacts. Material property changes alone had little to no effect on the maximum thoracic force or the maximum percent compression. With age, the thorax becomes stiffer due to superior rotation of the ribs, which can result in increased bone strain that can increase the risk of fracture. For the 70-YO models, the simulations predicted a higher number of rib fractures in comparison to the 30-YO models. The male models experienced more superior rotation of the ribs in comparison to the female models, which resulted in a higher number of rib fractures for the males.Conclusion: In this study, age- and sex-specific thoracic models were developed and the biomechanical response was studied using frontal and lateral impact simulations. The development of these age- and sex-specific FE models of the thorax will lead to an improved understanding of the complex relationship between thoracic geometry, age, sex, and injury risk.

Using Transmural Regularization and Dynamic Modeling for Noninvasive Cardiac Potential Imaging of Endocardial Pacing With Imprecise Thoracic Geometry

Cardiac electrical imaging from body surface potential measurements is increasingly being seen as a technology with the potential for use in the clinic, for example for pre-procedure planning or during-treatment guidance for ventricular arrhythmia ablation procedures. However several important impediments to widespread adoption of this technology remain to be effectively overcome. Here we address two of these impediments: the difficulty of reconstructing electric potentials on the inner (endocardial) as well as outer (epicardial) surfaces of the ventricles, and the need for full anatomical imaging of the subject's thorax to build an accurate subject-specific geometry. We introduce two new features in our reconstruction algorithm: a nonlinear low-order dynamic parameterization derived from the measured body surface signals, and a technique to jointly regularize both surfaces. With these methodological innovations in combination, it is possible to reconstruct endocardial activation from clinically acquired measurements with an imprecise thorax geometry. In particular we test the method using body surface potentials acquired from three subjects during clinical procedures where the subjects' hearts were paced on their endocardia using a catheter device. Our geometric models were constructed using a set of CT scans limited in axial extent to the immediate region near the heart. The catheter system provides a reference location to which we compare our results. We compare our estimates of pacing site localization, in terms of both accuracy and stability, to those reported in a recent clinical publication , where a full set of CT scans were available and only epicardial potentials were reconstructed.

EComment. Pectus excavatum surgical repair improves cardiopulmonary function in adults

Jayaramakrishnan et al. recently addressed the question: Does repair of pectus excavatum (PEx) improve cardiopulmonary function? [1]. Using an adequate keyword-based search strategy, the authors concluded that surgical repair using minimally invasive Nuss technique and Ravitch procedure caused an early, moderate decrease in pulmonary function tests (which are typically minimally impaired in PEx patients). In addition, cardiac function at rest improved during the early postoperative period, which is typically sustained in the mid-term. Here, we take the opportunity to mention that Jayaramakrishnan et al. have failed to identify our previous study based on a large series of 70 patients, which was recently published in the European Journal of Cardio-Thoracic Surgery [2]. We think this omission is critical regarding the clinical bottom-line proposed by Jayaramakrishnan et al. because our study clearly demonstrated that the modified Ravitch-type repair [3] in young adults significantly improved maximal oxygen uptake (VO2max) and O2 pulse [2]. Increase of O2 pulse (a surrogate of heart stroke volume) after surgery suggested that aerobic capacity (VO2max) improvement was the result of a better cardiovascular adaptation at maximal workload. In a short series of PE patients, we recently reported that normalization of thoracic geometry by PEx repair could restore adequate negative pulmonary pressure during ventilation (i.e., respiratory pump) that is necessary to enhanced venous return, heart filling and cardiac output [4, 5] . Overall, we would like to offer the possibility to include our results [2, 4] in the present evidence-based medicine proposal to support the conclusion by Jayaramakrishnan et al. [1] that PEx repair improves cardiopulmonary function and supports aerobic capacity. Conflict of interest: none declared.

Pectus excavatum repair improves cardiovascular function at maximal exercise by facilitating heart filling

The recent article by Tang et al. [1] supports the idea that Nuss repair improves cardiopulmonary exercise function in teenagers with moderate-to-severe pectus excavatum (PEx). We would like to congratulate the authors for this study and emphasize the relevance of this research, as well as their results, by making some brief remarks. First, the authors circumvented the difficulties in measuring cardiac output during exercise by using a gas-rebreathing technique, which has been previously validated in exercise testing conditions [2]. The authors demonstrated that Nuss-operated teenagers significantly increased their cardiac index at submaximal exercise. Postoperative increase of maximum exercise cardiac index was attributed in this study to enlargement of the thoracic dimension in the anterior–posterior plane facilitating heart filling and/or their better aerobic fitness due to increased physical activity. Second, Tang et al. [1] mentioned some of the study limitations, including the influence of growth and changes in sport habits on maximal exercise capacity. We feel that another important issue may be the misinterpretation of the relationship between cardiac performance and exercise limitation. Indeed, in healthy individuals, exercise tolerance is limited by the cardiovascular response and the degree of physical fitness, whereas no ventilation limitation is typically achieved [3]. In this setting, cardiac output is thus driven by oxygen demand, which increases with peripheral muscular exercise. In the Tang et al. study, teenagers experienced no changes in maximum oxygen uptake after Nuss repair, whereas cardiac output increased, which was mainly the result of increased maximal heart rate. One could interpret these findings as evidence of cardiovascular maladaptation, i.e. tachycardia, due to postoperative deconditioning. In a recent study [4], we confirm that PEx open repair [5] also can beneficially impact maximal exercise capacity in young adults. Although we did not directly measure the cardiac index, our results suggested that improved aerobic capacity was accompanied by increased oxygen pulse, a surrogate of stroke volume. We speculated that better postoperative aerobic capacity was directly related to improved haemodynamic conditions because such improvements were also observed in a series of athletes who experienced long-term, constant and heavy training protocols before and after PEx repair. Mechanisms by which cardiovascular function improves after PEx repair remain elusive. Normalization of thoracic geometry by PEx surgery can restore the adequate development of negative pulmonary pressure that is necessary to enhance venous return, heart filling and cardiac output. Consistently, we recently demonstrated that PEx repair improved the capacity of the inspiratory muscle system to generate intrathoracic negative pressure [6]. We speculated that postoperative increased respiratory pump efficacy to generate negative pulmonary pressure and to enhance venous return facilitates better cardiovascular adaptation at maximal exercise.

Three-dimensional stereoradiographic modeling of rib cage before and after spinal growing rod procedures in early-onset scoliosis

Background Early-onset scoliosis frequently leads to major thoracic deformity and pulmonary restrictive disease. Growing rods surgical techniques were developed to achieve a satisfactory correction of the spinal curves during growth. The effect on the rib cage deformity has not yet been documented. The purpose of this study was to analyze the changes of the thoracic geometry after implantation of a growing rod, and to evaluate a stereoradiographic reconstruction method among young scoliotic patients. Methods Four patients were enrolled in the study, and four additional patients in the reproducibility study. Three-dimensional spine and rib cage models were generated after low-dose stereoradiographic imaging (EOS). Three-dimensional parameters were computed before and after surgery. Intra and inter-observer reproducibility was calculated, and the accuracy was assessed in comparison to volumetric CT-scan. Findings The average Cobb angle was reduced from 50.8° to 26°. The surgery resulted in a complex 3D effect on the rib cage, combining frontal, lateral, and axial rotation. This effect was dependent of the side (concave or convex), and the position relative to the apical vertebra. Mean errors in comparison to CT-scan were 3.5 mm. Interpretation The results on the spinal deformity are comparable to other series. The effect on the rib cage is of a smaller magnitude than in the case of a spinal arthrodesis. A longer follow-up is necessary to confirm the positive effect on the rib cage deformity. Further research should be performed to improve the reproducibility of 3D parameters.

Ist die Kardiotoxizität der Radiotherapie im Rahmen des Brusterhalts überhaupt noch relevant, und könnte sie durch Mehrfelder-IMRT gesenkt werden?

Postoperative radiotherapy after breast cancer surgery effectively reduces local relapses. A survival benefit after breast conservation, however, has only been proven recently which was in part due to excessive cardiac mortality of patients who had been treated with radiotherapy in the past. The literature on postoperative radiotherapy for breast cancer was reviewed with regard to cardiac toxicity as the basis for hypothesis generation. From numerous publications on cardiac toxicity of breast cancer radiotherapy, the following pattern emerges: in series where a high radiation dose was applied to a significant percentage of the heart (postmastectomy and postlumpectomy series) cardiac toxicity/mortality was increased versus a nonexposed cohort or for left over right disease. If, however, a relevant exposure of cardiac muscle could be more or less excluded based on the technique used (mainly more recent postlumpectomy radiotherapy), no cardiac toxicity was observed. Series for which individual dose exposure varied or could not be clarified also came to varying conclusions. Also due to retrospectively unclear dose distributions, an exact quantification of tolerance doses/effects of different geographic dose distribution patterns could not be performed to date. A particularly difficult question to answer is the threshold volume for clinically relevant cardiotoxicity with tangential radiotherapy at prescription doses. As a consequence, this precludes an estimate in which situations multifield intensity-modulated radiotherapy (IMRT) with its characteristic dose distribution pattern of a larger volume exposed to intermediate doses and higher mean/median heart doses (as shown in Figure 1) might be preferable. This review updates the database on cardiac toxicity of breast cancer radiotherapy with special emphasis regarding the issues related to the clinical use of IMRT. Multifield IMRT may reduce the cardiac risk for a small subset of patients at excessive risk with conventional tangential radiotherapy due to unfavorable thoracic geometry, for whom partial-breast radiotherapy is not an option. Due to further concern about the effects of intermediate doses to larger heart volumes, potentially increased contralateral cancer risk and the long latency of clinically apparent toxicity, the introduction of breast IMRT should be closely followed. Accompanying functional studies may have the potential to detect cardiac toxicity at an earlier time.

Potential Effect of Robust and Simple IMRT Approach for Left-Sided Breast Cancer on Cardiac Mortality

Three-dimensional (3D) treatment planning has reduced the cardiac dose in postoperative radiotherapy for breast cancer; however, the overall cardiac toxicity is still an issue because of more aggressive adjuvant treatment. Toxicity models have suggested that a reduction of the heart volume treated to high doses might be particularly advantageous. We compared aperture-based multifield intensity-modulated radiotherapy (IMRT) plans to 3D-planned tangent fields using dose-volume histograms, cardiac toxicity risk, and the robustness to positioning errors. For 14 computed tomography data sets of patients with left-sided breast cancer (unfavorable thoracic geometry), a 3D treatment plan and an IMRT plan were created. The dose-volume histograms were evaluated for the target and risk organs. Excess risk of cardiac mortality was calculated for both approaches using a relative seriality model. Positioning errors were simulated by moving the isocenter. IMRT reduced the maximal dose to the left ventricle by a mean of 30.9% (49.14 vs. 33.97 Gy). The average heart volume exposed to >30 Gy was reduced from 45 cm(3) to 5.84 cm(3). The mean dose to the left ventricle was reduced by an average of 10.7% (10.86 vs. 9.7 Gy), and the mean heart dose increased by an average of 24% (from 6.85 to 8.52 Gy). The model-based reduction of the probability for excess therapy-associated cardiac death risk was from 6.03% for the 3D plans to 0.25% for the IMRT plans. Aperture-based IMRT for left-sided breast cancer significantly reduces the maximal dose to the left ventricle, which might translate into reduced cardiac mortality. Biological modeling might aid in deciding to treat with IMRT but has to be validated prospectively.

A Simulation Study on the Effect of Thoracic Conductivity Inhomogeneities on Sensitivity Distributions

A high-resolution 3D finite difference model of the electrical conductivity distribution in a human thorax based on a 43-slice MRI data set along with lead field theory was used to examine the effect of thoracic conductivity inhomogeneities on sensitivity distributions. The electrode configurations used in the present study were based on an eight-electrode array positioned evenly around the thoracic model at a level close the nipple line. Sensitivity distributions of each possible adjacent pair current excitation pattern for both the homogeneous thoracic model and the heterogeneous thoracic model were evaluated. The results show that thoracic inhomogeneities significantly perturb sensitivity distribution patterns. Although for a given thoracic geometry the electrode configuration gives the overall sensitivity distribution features, sharp large local changes occur near the boundaries between different tissues in the heterogeneous model. The results of sensitivity distributions of the heterogeneous thoracic model demonstrate the feasibility of impedance source localization. Selectivity can be used to as a guide to finding favorable electrode configuration for regional impedance monitoring.

Thoracic geometry changes during equine locomotion

AbstractClassic descriptions of rib motion during ventilation include three-dimensional movements that are tied to the locomotor pattern. It is still not clear how chest wall and diaphragmatic movements contribute to ventilation. The purpose of this paper was to evaluate how gait affects local thoracic geometry in horses. Hemispherical markers were placed on the skin over the ribs and spine to calculate thoracic hemi-diameter. Ventilatory airflows were recorded using an ultrasonic flowmeter system. Airflow and kinematic data were collected synchronously at walk (1.8 m s-1), trot (4 m s-1), canter and gallop (6, 8 and 10 m s-1) on the treadmill. At walk and trot, the changes in right and left hemi-diameter were approximately symmetric. At walk, mean hemi-diameter changes were 40 mm (rib 10) and 47 mm (rib 16). At trot, they were 33 mm (rib 10) and 34 mm (rib 16). Across the three canter and gallop speeds, leading (right) side hemi-diameter change increased from 25 to 30 to 35 mm (rib 10) and from 23 to 37 to 46 mm (rib 16). The trailing (left) side hemi-diameter increased from 50 to 67 to 70 mm (rib 10) and from 36 to 48 to 54 mm (rib 16) (P≪0.01). At canter and gallop, the non-lead side of the thorax is subjected to larger amplitude changes in hemi-diameter than the lead side, which tends to be more compressed overall and demonstrates smaller amplitudes of change in diameter.

Integrated head-thoracic vascular MRI at 3 T: Assessment of cranial, cervical and thoracic involvement of giant cell arteritis

Recently, high-resolution contrast-enhanced MRI has proven to be feasible for noninvasive diagnosis of giant cell arteritis in the cranium. In such examinations, thickening of the vessel wall and/or increased contrast enhancement demonstrate mural inflammation. Typically, the superficial cranial arteries with predominance of the superficial temporal artery are affected by the disease. However, giant cell arteritis can also involve other parts of the vascular system and an examination with extended coverage, including head, neck, and thorax would be advantageous. In this study, a novel approach for integrated head-thoracic vascular MRI at 3 T is presented. Combining first-pass imaging of a single-dose contrast agent with post-contrast imaging permits the assessment of both thoracic aortic geometry and wall, in addition to high-resolution head imaging needed for the analysis of the small superficial cranial arteries. Results from a patient feasibility study are presented and confirm that the protocol can successfully be completed in less than 40 min.

Thoracic geometry and its relation to electrical current distribution: consequences for electrode placement in electrical impedance cardiography.

In thoracic impedance cardiography (TIC) measurements the neck electrodes are often positioned at the basis of the neck, close to the neck-thorax transition. Theoretically, this neck-thorax transition will cause inhomogeneities in the current density and potential distribution. This was simulated using a 3D finite element method, solely representing the geometrical neck-thorax transition. The specific conductivity was 7 10(-3) (omega cm)-1 and the injected current was 1 mA. As expected, the model generated inhomogeneities in the current distribution at the neck-thorax transition, which reached as far as 5 cm into the neck and 20 cm into the thorax. These results are supported by in vivo measurements performed in 10 young male subjects, in which the position of the neck electrodes was varied. A two-way ANOVA revealed that the stroke volume of the lowest neck position was significantly different from the other positions. Small shifts in the position of the neck electrode resulted in large changes in impedance and stroke volume (127 to 82 ml for the Kubicek equation). To standardise the electrode position, the authors strongly recommend placement of the neck electrodes at least 6 cm above the clavicula.