Browsing by Subject "Organ"

Purpose:

The overall purpose of this study was a comparison of radiation exposure for patients and staff during intra-operative imaging for orthopedic lumbar spine surgery. In order to achieve this, we: (1) Characterized each x-ray machine for physics performance, (2) Measured occupational radiation exposure inside the surgical suite for multiple intra-operative imaging devices utilizing currently in place clinical protocols for abdominal/spinal imaging, and (3) Measured specific organ doses for a phantom of three different Body Mass Indices (BMI) for each machine. We also compared the dose changes relative to changes in BMI as well as surgical image quality changes relative to BMI. This served as the majority of the first phase of a two phase project. The purpose of the second phase of the project will be to optimize scan parameters for surgical hardware placement in terms of image quality and organ dose for the devices that allow for modifications of scanner settings.

Materials and Methods:

(1) X-Ray quality control meters were used to verify particular beam characteristics and additional information was calculated from the beam data. Both a small volume ionization chamber as well as Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) dosimeters were used to validate linear response of new design X-Ray tubes. (2) Both handheld ionization chamber survey meters as well as Geiger-Muller based personal dose meters were used to measure stray radiation for room surveys in locations representative of typical radiation worker positions during intra-operative imaging. (3) MOSFET dosimeters were placed in an adult male anthropomorphic phantom representing a normal BMI. 20 MOSFETs were used in nine organs with two small volume ion chambers used for skin surface dosimetry. Two additional layers of adipose equivalent material were progressively added to the phantom to represent BMI values of overweight and obese.

Results:

(1) The maximum tube potential, half value layer (HVL), effective energy, and soft tissue f-factor for each machine is as follows: IMRIS VISIUS iCT: 118.4 kVp, 7.66 mm Al, 53.64 keV, and 0.934 cGy/R; Mobis Airo: 122.3 kVp, 7.21 mm Al, 51.31 keV, and 0.925 cGy/R; Siemens ARCADIS Orbic 3D: 83 kVp, 7.12 mm Al, 32.76 keV, and 0.914 cGy/R; GE OEC 9900 Elite: 75 kVp, 4.25 mm Al, 46.6 keV, and 0.920 cGy/R. (2) The highest exposure rates measured during clinically implemented protocols for each scanner are as follows: IMRIS VISIUS iCT: 800 mR/hr; Mobis Airo: 6.47 R/hr; Siemens ARCADIS Orbic 3D: 26.4 mR/hr. (3) The effective dose per scan of each device for a full lumbar spine scan are as follows, for normal, overweight, and obese BMI, respectively: IMRIS VISIUS iCT: 12.00 ± 0.30 mSv, 15.91 ± 0.75 mSv, and 23.23 ± 0.55 mSv; Mobius Airo: 5.90 ± 0.25 mSv, 4.97 ± 0.12 mSv, and 3.44 ± 0.21 mSv; Siemens ARCADIS Orbic 3D: 0.30 ± 0.03 mSv, 0.39 ± 0.02 mSv, and 0.28 ± 0.03 mSv; GE OEC 9900 Elite: 0.44 mSv, 0.77 mSv, and 1.14 mSv.

Conclusion:

(1) The IMRIS VISIUS iCT i-Fluoro capable CT scanner and Mobius Airo mobile CT scanner have similar beam characteristics with significantly different tube parameter modulation protocols. Siemens ARCADIS Orbic 3D and GE OEC 9900 offer comparable beam characteristics but different imaging methods. All scanners performed within factory specifications. (2) The IMRIS VISIUS iCT should not be used in i-Fluoro mode for surgical procedures active during scanning due to the 1.42 cGy/s point dose rate in the beam field. The high exposure rate from the Mobius Airo is offset by short scan times and can be mitigated by ensuring enforcement of currently established radiation protection regulations and policies. Minimal stray radiation is measured from the Siemens ARCADIS Orbic 3D. (3) The differences in tube modulation of the CT scanners means the Mobius Airo offers a significantly reduced effective dose with increasing patient BMI over the IMRIS VISIUS iCT. Effective dose from the CT scanners varies as much as one to two orders of magnitude higher than the C Arms, but the Siemens ARCADIS Orbic 3D offers unusable image quality for patients with higher than normal BMI. Based off of physician reported usable surgical image quality of Mobius Airo, this device is recommended for continued integration and implementation during routine surgical procedures for patients of all BMI in orthopedic lumbar spine surgery.

This dissertation seeks to reevaluate French repertoire for the organ in the broader context of French music and society in the years between the two world wars. I argue that leading composers for the instrument were not cloistered between the musically conservative walls of the church but were rather fully engaged in cultural and musical shifts occurring across the Parisian musical scene. By analyzing music of Louis Vierne, Jehan Alain, and Olivier Messiaen, I address different ways in which these composers wrote for the organ in the early twentieth century as well as ways in which these composers engaged the world around them. Louis Vierne – older than Alain and Messiaen by forty years – represents an older generation rooted in late nineteenth- century romanticism. The way in which he composed for the organ was not only influenced by composers around him but also in the links to French musical heritage of the eighteenth and nineteenth centuries. Alain and Messiaen – born three years apart – were colleagues who shared similar interests and were inspired by influences beyond the borders of the church and the state. For these composers, the organ was not an instrument tethered to conservative styles of composition but rather one that was fully able to engage with contemporary musical styles and absorb outside influence just as much as music of other genres and for other instruments.

Purpose: Radiation doses from computed tomography (CT) examinations have come under public and governmental scrutiny because of several recent misadministrations of radiation across the country. Current CT dosimetry methods in the clinic use standardized cylindrical water phantoms to measure radiation dose across various scanning protocols and different scanner manufacturers. These methods and equipment are too generalized to provide accurate risk assessment for patients of varying ages, genders, and anatomies. The advent of computer models based on real CT imaged anatomy has made patient specific and organ specific dosimetry achievable.

With a population of both pediatric and adult patient models comprised of a wide range of anatomies, Monte Carlo based dose calculations can be cataloged. A patient can receive a prospective dose estimation from a phantom within our population that best exhibits the patient's age and anatomical characteristics. Knowledge of organ size and location is essential to finding a proper match between the patient and the computer model. To this end, very little information is currently available regarding organ size and location across a diverse human population. The purpose of this study was to develop a predictive model to ascertain organ locations and volumes for pediatric and adult patients.

Methods: This study included 51 adults and 40 pediatrics from which Extended NURBS-based Cardiac-Torso (XCAT) phantoms were generated. Large organs were manually segmented from clinical CT data. The remaining organs and other anatomical structures were created by transforming an existing human model template to fit the framework of the segmented structures. The maximum and minimum points of the organs were recorded with respect to the axial distance from the tip of the sacrum. The axial width and midpoint for each organ were then determined. The organ volumes were also calculated. All three organ parameters were plotted as functions of patient age and weight for adults and patient age for pediatrics.

Results: The adult patients showed no statistically significant correlation between organ parameters and age and BMI. There were slight, positive linear trends with organ midpoint (max r2=0.365, mean r2=0.185) and organ volume (max r2=0.510, mean r2=0.183) versus adult patient weight. The height correlations were also positive for midpoint (r2=0.485, mean r2=0.271). Gaussian fits performed on probability density functions of adult organs resulted in r2-values ranging from 0.945 to 0.996. Pediatric patients demonstrated strong cube root relationships with organ midpoints (max r2=0.857, mean r2=0.790) and organ widths (max r2=0.905 , mean r2=0.564) versus age. Pediatric organ volumes showed positive linear relationships versus age (max r2=0.983, mean r2=0.701).

Conclusions: Adult patients exhibited small variations in organ volume and location with respect to weight, but no meaningful correlation existed between these parameters and age. Once adulthood is reached, organ morphology and positioning seems to remain static; however, clear trends are evident between pediatric age and organ volumes and locations. Such information can aid in the selection of an appropriate computer model that has the highest probability of mirroring the anatomy of a patient undergoing a clinical exam. Applications could also extend into comparing PET versus CT determination of organ volume and location.