Dynamic Chemical Shift Imaging for Image-Guided Thermal Therapy

Magnetic resonance temperature imaging (MRTI) is recognized as a noninvasive means to provide temperature imaging for guidance in thermal therapies. The most common method of estimating temperature changes in the body using MR is by measuring the water proton resonant frequency (PRF) shift. Calculation of the complex phase difference (CPD) is the method of choice for measuring the PRF indirectly since it facilitates temperature mapping with high spatiotemporal resolution. Chemical shift imaging (CSI) techniques can provide the PRF directly with high sensitivity to temperature changes while minimizing artifacts commonly seen in CPD techniques. However, CSI techniques are currently limited by poor spatiotemporal resolution. This research intends to develop and validate a CSI-based MRTI technique with intentional spectral undersampling which allows relaxed parameters to improve spatiotemporal resolution. An algorithm based on autoregressive moving average (ARMA) modeling is developed and validated to help overcome limitations of Fourier-based analysis allowing highly accurate and precise PRF estimates. From the determined acquisition parameters and ARMA modeling, robust maps of temperature using the k-means algorithm are generated and validated in laser treatments in ex vivo tissue. The use of non-PRF based measurements provided by the technique is also investigated to aid in the validation of thermal damage predicted by an Arrhenius rate dose model.

A model of the roles of essential kinases in the induction and expression of late long-term potentiation.

The induction of late long-term potentiation (L-LTP) involves complex interactions among second-messenger cascades. To gain insights into these interactions, a mathematical model was developed for L-LTP induction in the CA1 region of the hippocampus. The differential equation-based model represents actions of protein kinase A (PKA), MAP kinase (MAPK), and CaM kinase II (CAMKII) in the vicinity of the synapse, and activation of transcription by CaM kinase IV (CAMKIV) and MAPK. L-LTP is represented by increases in a synaptic weight. Simulations suggest that steep, supralinear stimulus-response relationships between stimuli (e.g., elevations in [Ca(2+)]) and kinase activation are essential for translating brief stimuli into long-lasting gene activation and synaptic weight increases. Convergence of multiple kinase activities to induce L-LTP helps to generate a threshold whereby the amount of L-LTP varies steeply with the number of brief (tetanic) electrical stimuli. The model simulates tetanic, -burst, pairing-induced, and chemical L-LTP, as well as L-LTP due to synaptic tagging. The model also simulates inhibition of L-LTP by inhibition of MAPK, CAMKII, PKA, or CAMKIV. The model predicts results of experiments to delineate mechanisms underlying L-LTP induction and expression. For example, the cAMP antagonist RpcAMPs, which inhibits L-LTP induction, is predicted to inhibit ERK activation. The model also appears useful to clarify similarities and differences between hippocampal L-LTP and long-term synaptic strengthening in other systems.

Molecular events associated with trisomy of chromosome 7 in mouse skin chemical carcinogenesis

The primary objective of this study has been to investigate the effects at the molecular level of trisomy of mouse chromosome 7 in chemically induced skin tumors. It was previously proposed that the initiation event in the mouse skin carcinogenesis model is a heterozygous mutation of the Ha-ras-1 gene, mapped to chromosome 7. Previous studies in this laboratory identified trisomy 7 as one of the primary nonrandom cytogenetic abnormalities found in the majority of severely dysplastic papillomas and squamous cell carcinomas induced in SENCAR mice by an initiation-promotion protocol. Therefore, the first hypothesis tested was that trisomy 7 occurs by specific duplication of the chromosome carrying a mutated Ha-ras-1 allele. Results of a quantitative analysis of normal/mutated allelic ratios of the Ha-ras-1 gene confirmed this hypothesis, showing that most of the tumors exhibited overrepresentation of the mutated allele in the form of 1/2, 0/3, and 0/2 (normal/mutated) ratios. In addition, histopathological analysis of the tumors showed an apparent association between the degree of malignancy and the dosage of the mutated Ha-ras-1 allele. To determine the mechanism for loss of the normal Ha-ras-1 allele, found in 30% of the tumors, a comparison of constitutional and tumor genotypes was performed at different informative loci of chromosome 7. By combining Southern blot and polymerase chain reaction fragment length polymorphism analyses of DNAs extracted from squamous cell carcinomas, complete loss of heterozygosity was detected in 15 of 20 tumors at the Hbb locus, and in 5 of 5 tumors at the int-2 locus, both distal to Ha-ras-1. In addition, polymerase chain reaction analysis of DNA extracted from papillomas indicated that loss of heterozygosity occurs in late-stage lesions exhibiting a high degree of dysplasia and areas of microinvasion, suggesting that this event may be associated to the acquisition of the malignant phenotype. Allelic dosage analysis of tumors that had become homozygous at Hbb but retained heterozygosis at Ha-ras-1, indicated that loss of heterozygosity on mouse chromosome 7 occurs by a mitotic recombination mechanism. Overall, these findings suggest the presence of a putative tumor suppressor locus on the 7F1-ter region of mouse chromosome 7. Thus, loss of function by homozygosis at this putative suppressor locus may complement activation of the Ha-ras-1 gene during tumor progression, and might be associated with the malignant conversion stage of mouse skin carcinogenesis. ^

Genetic analysis of tumor progression susceptibility in the mouse skin model

In the field of chemical carcinogenesis the use of animal models has proved to be a useful tool in dissecting the multistage process of tumor formation. In this regard the outbred SENCAR mouse has been the strain of choice in the analysis of skin carcinogenesis given its high sensitivity to the chemically induced acquisition of premalignant lesions, papillomas, and the later progression of these lesions into squamous cell carcinomas (SCC).^ The derivation of an inbred strain from the SENCAR stock called SSIN, that in spite of a high sensitivity to the development of papillomas lack the ability to transform these premalignant lesions into SCC, suggested that tumor promotion and progression were under the genetic control of different sets of genes.^ In the present study the nature of susceptibility to tumor progression was investigated. Analysis of F1 hybrids between the outbred SENCAR and SSIN mice suggested that there is at least one dominant gene responsible for susceptibility to tumor progression.^ Later development of another inbred strain from the outbred SENCAR stock, that had sensitivity to both tumor promotion and progression, allowed the formulation of a more accurate genetic model. Using this newly derived line, SENCAR B/Pt. and SSIN it was determined that there is one dominant tumor progression susceptibility gene. Linkage analysis showed that this gene maps to mouse chromosome 14 and it was possible to narrow the region to a 16 cM interval.^ In order to better characterize the nature of the progression susceptibility differences between these two strains, their proliferative pattern was investigated. It was found that SENCAR B/Pt, have an enlarged proliferative compartment with overexpression of cyclin D1, p16 and p21. Further studies showed an aberrant overexpression of TGF-$\beta$ in the susceptible strain, an increase in apoptosis, p53 protein accumulation and early loss of connexin 26. These results taken together suggest that papillomas in the SENCAR B/Pt. mice have higher proliferation and may have an increase in genomic instability, these two factors would contribute to a higher sensitivity to tumor progression. ^