Positron emission tomography (PET) tumor segmentation and quantification: Development of new algorithms

Tumor functional volume (FV) and its mean activity concentration (mAC) are the quantities derived from positron emission tomography (PET). These quantities are used for estimating radiation dose for a therapy, evaluating the progression of a disease and also use it as a prognostic indicator for predicting outcome. PET images have low resolution, high noise and affected by partial volume effect (PVE). Manually segmenting each tumor is very cumbersome and very hard to reproduce. To solve the above problem I developed an algorithm, called iterative deconvolution thresholding segmentation (IDTS) algorithm; the algorithm segment the tumor, measures the FV, correct for the PVE and calculates mAC. The algorithm corrects for the PVE without the need to estimate camera's point spread function (PSF); also does not require optimizing for a specific camera. My algorithm was tested in physical phantom studies, where hollow spheres (0.5-16 ml) were used to represent tumors with a homogeneous activity distribution. It was also tested on irregular shaped tumors with a heterogeneous activity profile which were acquired using physical and simulated phantom. The physical phantom studies were performed with different signal to background ratios (SBR) and with different acquisition times (1-5 min). The algorithm was applied on ten clinical data where the results were compared with manual segmentation and fixed percentage thresholding method called T50 and T60 in which 50% and 60% of the maximum intensity respectively is used as threshold. The average error in FV and mAC calculation was 30% and -35% for 0.5 ml tumor. The average error FV and mAC calculation were ~5% for 16 ml tumor. The overall FV error was ∼10% for heterogeneous tumors in physical and simulated phantom data. The FV and mAC error for clinical image compared to manual segmentation was around -17% and 15% respectively. In summary my algorithm has potential to be applied on data acquired from different cameras as its not dependent on knowing the camera's PSF. The algorithm can also improve dose estimation and treatment planning.^

Positron Emission Tomography (PET) Tumor Segmentation and Quantification: Development of New Algorithms

Tumor functional volume (FV) and its mean activity concentration (mAC) are the quantities derived from positron emission tomography (PET). These quantities are used for estimating radiation dose for a therapy, evaluating the progression of a disease and also use it as a prognostic indicator for predicting outcome. PET images have low resolution, high noise and affected by partial volume effect (PVE). Manually segmenting each tumor is very cumbersome and very hard to reproduce. To solve the above problem I developed an algorithm, called iterative deconvolution thresholding segmentation (IDTS) algorithm; the algorithm segment the tumor, measures the FV, correct for the PVE and calculates mAC. The algorithm corrects for the PVE without the need to estimate camera’s point spread function (PSF); also does not require optimizing for a specific camera. My algorithm was tested in physical phantom studies, where hollow spheres (0.5-16 ml) were used to represent tumors with a homogeneous activity distribution. It was also tested on irregular shaped tumors with a heterogeneous activity profile which were acquired using physical and simulated phantom. The physical phantom studies were performed with different signal to background ratios (SBR) and with different acquisition times (1-5 min). The algorithm was applied on ten clinical data where the results were compared with manual segmentation and fixed percentage thresholding method called T50 and T60 in which 50% and 60% of the maximum intensity respectively is used as threshold. The average error in FV and mAC calculation was 30% and -35% for 0.5 ml tumor. The average error FV and mAC calculation were ~5% for 16 ml tumor. The overall FV error was ~10% for heterogeneous tumors in physical and simulated phantom data. The FV and mAC error for clinical image compared to manual segmentation was around -17% and 15% respectively. In summary my algorithm has potential to be applied on data acquired from different cameras as its not dependent on knowing the camera’s PSF. The algorithm can also improve dose estimation and treatment planning.

La ciudad, el poeta y su familia melancolica (Poesia Chilena de los ultimos 50 anos)

This dissertation explored the relationship among poets, cities, and the construction of nation-ness. It was an interpretive reading of Chilean poetry and Chilean-ness as a way of inventing the nation from its very origins, starting with the colonial epic poem La Araucana and the founding of Santiago, its capital city. In this dissertation, poetry not only dealt with cities or "city poets" but also with the very conception, drafting, and systematic invention of cities as a "dream of order". The construct of a "community" of Chileans has maintained family ties with "Melancholy" in the collective imagination. This structure of melancholy reinforced the idea of "an order and a community" passed along by poets through generations. This dissertation also explored the moment when this melancholic family was fractured, divided, and Santiago was darkened by the events of September 11, 1973 and the rise of dictatorship, brutality, and censorship. ^ The methodology employed to examine different aspects of the construction of the city-nation included theoretical approaches such as Benedict Anderson's idea of nations as "imagined communities," Ángel Rama's analysis of Latin American urban rationality in his book The Lettered City , and the idea of the poet as an urban seer or visionary, the "flâneur" studied by Walter Benjamin in Charles Baudelaire's poetry. A central finding was that this "imagined community" have been severely transformed since 1950. In Chilean poetry, two works served as major referents: Pablo Neruda's Canto General, a totalizing idea of collective identity carved from the stones of the ruins of Machu Picchu, and Nicanor Parra's Poemas y Antipoemas (1954), which begun to illustrate the slow "decomposition" of the "The Lettered City." Among such conflicting images of (post-)modernity, poet Enrique Lihn became the central counter-figure who put an end to a long tradition of producing canonical nation-building cultural artifacts. His book El paseo Ahumada (1983) impacted the new generations of Chilean poets. The conclusion brought together the five-century history and diverse poetic experiences of the traditional Lettered City with the latest currents of marginalized urban poetry (1987-2003), the so-called "barbarians," flâneurs who were (re)inventing Chilean-ness in the globalized, and anti-Utopian city of "Sanhattan." ^