Bringing Interventional Radiology to Mars!

At present, astronauts on space missions can get medical assistant from Earth. In the future, deep space missions such as missions to Mars will delay communication with physicians on Earth, making it impossible to get immediate support in urgent medical situations. On the spaceship, a polyvalent physician-astronaut could mainly perform small surgery and traumatology procedures. Interventional Radiology (IR) allows minimally invasive interventions and requires small devices. In these conditions of space constrains, IR presents significant benefits. To guarantee the technical realization of specific medical interventions during deep space missions, a team composed of interventional radiologists and space engineers, is developing the IR toolbox. The development of the toolbox intents to minimize the volume/weight of medical devices and to ensure the safety requirements for the crew. New scenarios of IR interventions have been developed to adapt the interventions to the spatial context, making possible the treatment of pathologies that are otherwise, on Earth, optimally treated surgically. Interventional radiology has a major role to play in the management of acute medical problems which may occur in the future story of deep space missions to the Moon, and further to Mars.

Study of the reliability of quantification methods of dynamic contrast-enhanced ultrasonography: numerical modeling of blood flow in tumor microvascularization.

Dynamic contrast-enhanced ultrasonography is a recent functional dynamic imaging technique that allows evaluation of the efficacy of anti-angiogenic treatments by quantifying changes in specific parameters of the tumor vasculature. Preclinical and clinical experimental studies now reveal the existence of sources of variability in the quantitative methods. In order to study the reliability of quantification methods (both semi-quantitative and quantitative), we have developed the first numerical model of blood flow and contrast agents in vascular networks with computational fluid dynamics Fluent software version 15.0 (ANSYS, France). We studied four vascular networks (1.84 × 10-3, 2.28 × 10-3, 2.4 × 10-3 and 2.54 × 10-3 ml) and four blood velocities (0.01, 0.02, 0.03 and 0.05 m s-1). For variations in tumor vascular volume the quantitative method is more sensitive, with variations of parameter perfusion of 25.7%, in contrast to variations of the semi-quantitative parameters between 14.9 and 19.5%. For changes in blood velocity the semi-quantitative method is more sensitive, with variation of the area under the enhancement curve (64%), the maximum of the enhancement curve (60%), and the slope of the enhancement curve (73%). The transit time parameters from the two quantitative methods were weakly sensitive to both blood volume and blood flow variations. This study is hopeful and may be extended to the treatment of more complex vascular networks, to approach clinical conditions, and to the evaluation of quantification methods in contrast imaging.

Accuracy and Precision of Seven Radiography-Based Measurement Methods of Vertebral Axial Rotation in Adolescent Idiopathic Scoliosis.

STUDY DESIGN: Assessment of vertebral axial rotation measurement methods. OBJECTIVES: To assess the accuracy and precision of seven radiography-based vertebral axial rotation measurement methods for typical scoliotic deformity before and after posterior instrumentation. SUMMARY OF BACKGROUND DATA: Vertebral axial rotation is an important component to evaluate transverse plane scoliotic deformities. Several measurement methods were developed based on coronal plane radiographs or computerized 3D reconstruction. Their ability to accurately and precisely measure axial rotation, either pre- or postoperatively, is not well known. METHODS: Two synthetic vertebrae, with and without instrumentation, were fixed in a jig allowing 3D rotation manipulations. Fifty-three configurations of 3D rotations were radiographed. Two observers evaluated seven measurement methods: one visual estimation, two ruler-based (Nash-Moe and Perdriolle), one analytical (Stokes), and three 3D-reconstruction techniques (based on pedicles, based on eight vertebra landmarks, and a surface-based reconstruction software SterEOS). Measurements were repeated one week later. RESULTS: Intraobserver precision ranged from 2.0° (Perdriolle/SterEOS) to 3.6° (visual estimation) for the noninstrumented vertebra, and from 2.2° (SterEOS) to 9.7° (Nash-Moe) for the instrumented vertebra. Interobserver precision ranged from 1.2° (SterEOS) to 9.3° (Nash-Moe) for the noninstrumented vertebra, and from 1.7° (SterEOS) to 6.2° (Visual Estimation) for the instrumented vertebra. Accuracy of the methods ranged from 2.1° with SterEOS to 9.1° with Nash-Moe ruler. The measurement error was significantly associated with the level of axial rotation for Nash-Moe and 3D reconstruction techniques with low to moderate correlation. CONCLUSIONS: The majority of radiography-based methods measured vertebral axial rotation with an average error of 2° to 5°. The Nash-Moe method should be avoided, considering its inaccuracy greater than 9°. The instrumentation did not compromise the precision or the accuracy of measurement. The measurement accuracy of 3D reconstruction methods was impaired by the severity of the axial rotation. LEVEL OF EVIDENCE: N/A.

Implant Density at the Apex Is More Important Than Overall Implant Density for 3D Correction in Thoracic Adolescent Idiopathic Scoliosis Using Rod Derotation and En Bloc Vertebral Derotation Technique.

STUDY DESIGN: Biomechanical analysis of 3D correction and bone-screw forces through numerical simulations of scoliosis instrumentation with different pedicle screw patterns. OBJECTIVE: To analyze the effect of different screw densities and distributions on 3D correction and bone-screw forces in adolescent idiopathic scoliosis (AIS) instrumentation. SUMMARY OF BACKGROUND DATA: Instrumentation constructs with various numbers of pedicle screws and patterns have been proposed for thoracic AIS instrumentation. However, systematic biomechanical studies have not yet been completed on the appropriate screw patterns for optimal 3D correction. METHODS: Patient-specific biomechanical models of the spine were created for 10 AIS cases (Lenke 1). For each case, surgical instrumentation patterns were computationally simulated using respectively a reference screw pattern (two screws per level fused) and six alternative screw patterns with fewer screws. Simulated surgical maneuvers and model definition were unchanged between simulations except the number and distribution of screws. 3D correction and bone-screw forces were compared. RESULTS: A total of 140 posterior instrumentations were computationally simulated. Mean corrections in the coronal and sagittal planes with alternative screw patterns were within 4° to the reference pattern. Increasing screw density in the apical region from one to two screws per level improved percent apical vertebral rotation (AVR) correction (r = 0.887, P < 0.05). Average bone-screw force associated with the reference screw pattern was 243N ±â€Š54N and those with the alternative screw patterns were 11% to 48% lower. CONCLUSION: Compared with the reference maximal screw density pattern, alternative screw patterns allowed similar corrections in the coronal and sagittal planes. AVR correction was strongly correlated with screw density in the apical region; AVR correction varied significantly with screw patterns of the same overall screw density when an en bloc vertebral derotation technique was simulated. High screw density tended to overconstrain the instrumented spine and resulted in higher forces at the bone-screw interface. LEVEL OF EVIDENCE: N/A.

How does differential rod contouring contribute to 3-dimensional correction and affect the bone-screw forces in adolescent idiopathic scoliosis instrumentation?

BACKGROUND: Differential rod contouring is used to achieve 3-dimensional correction in adolescent idiopathic scoliosis instrumentations. How vertebral rotation correction is correlated with the amount of differential rod contouring is still unknown; too aggressive differential rod contouring may increase the risk of bone-screw connection failure. The objective was to assess the 3-dimensional correction and bone-screw forces using various configurations of differential rod contouring. METHODS: Computerized patient-specific biomechanical models of 10 AIS cases were used to simulate AIS instrumentations using various configurations of differential rod contouring. The tested concave/convex rod configurations were 5.5/5.5 and 6.0/5.5mm diameter Cobalt-chrome rods with contouring angles of 35°/15°, 55°/15°, 75°/15°, and 85°/15°, respectively. 3-dimensional corrections and bone-screw forces were computed and analyzed. FINDINGS: Increasing the difference between the concave and convex rod contouring angles from 25° to 60°, the apical vertebral rotation correction increased from 35% (SD 17%) to 68% (SD 24%), the coronal plane correction changed from 76% (SD 10%) to 72% (SD 12%), the thoracic kyphosis creation from 27% (SD 60%) to 144% (SD 132%), and screw pullout forces from 94N (SD 68N) to 252N (SD 159N). Increasing the concave rod diameter to 6mm resulted in increased transverse and coronal plane corrections, higher thoracic kyphosis, and screw pullout forces. INTERPRETATIONS: Increasing the concave rod contouring angle and diameter with respect to the convex rod improved the transverse plane correction but with significant increase of screw pullout forces and thoracic kyphosis. Rod contouring should be planned by also taking into account the 3-dimensional nature and stiffness of the curves and combined with osteotomy procedures, which remains to be studied.