New method for small animal molecular imaging developed

Thayer School of Engineering professor Brian Pogue and his research team introduced a new small animal imaging system that greatly enhanced the performance of current fluorescence tomography (FT) and may eventually aid in cancer therapy for humans. The findings were published in Review of Scientific Instruments.

To target the problem of poor resolution in current FT imaging, the research team employed X-ray microcomputed tomography (microCT), an anatomical imaging modality. The two systems complement each other: FT increases the sensitivity of microCT to cancerous tissues thereby enhancing contrast, while microCT improves quantitative accuracy of the FT by reconstructing the volumetric images of interest. Further, the new FT imaging system counts single photons for maximum sensitivity.

The researchers expect this microCT-coupled FT system, which provides more accurate small animal molecular imaging, to be applied in preclinical cancer research as well as cancer therapy.

Physiology & Medicine

Bypass surgery using a pig heart.

Pig organs and new drugs combat transplantation challenges

Pathology plays a key role in emerging transplant methods according to Henry Tazelaar from the Mayo Clinic College of Medicine, 2009’s Miguel Marin-Padilla Lecturer. The problem with transplants is that the recipient is susceptible to hyperacute rejections, organary cell rejection, and other infections. Tazelaar explained that the development of immunosuppressive agents has improved post-transplant survival rates.

To cope with donor shortages, mechanical devices, organogenesis, and suboptimal organ came to light. Now, new ideas of xenotransplantation emerged. Xenotransplantation is a between-species transplant. Recent research has focused on pig heart transplants in primate models.

Genetic modifications of the donor pigs can delay xenograft rejections. Primate models have survived as long as 120 days without rejection, but still remain susceptible to the same risks as normal transplants, such as myocyte vacuolization and vascular congestion that can result in either thrombosis or coagulative necrosis. For now, pathologists continue to strive towards improving transplant success.

Physics & Astronomy

Breakthrough in space imaging sheds light on the universe

The universe remains a mystery – 99.9% of the universe is still unmapped. Avi Leob, director of the Institute for Theory and Computation of Harvard University, discussed two new methods for mapping the universe’s most elusive phenomena.

The first method observes gravity on a cosmological scale by mapping the distribution of hydrogen based on its resonant 21 cm emission wavelength. The emissions reveal density fluctuations of the universe before the galaxies were formed while the dense pockets formed from residual hydrogen after reionization can trace large-scale structures. The other method observes black holes by the effects of their strong field gravity.

Once scientists refine the resolution enough to produce an accurate, undistorted image, this method should allow imaging of the black hole’s silhouette in the Milky Way galaxy SgrA*, a current interest of scientists. Direct imaging of the nearest supermassive black hole should be possible in the near future.

“In my view, this would be a Nobel Prize winning image, as this would appear in all the textbooks of general relativity. This is a confirmation of one of the predictions of Einstein’s theory of gravity that has not yet been observed,” Leob said regarding the study’s potential success.

Computer Science

Digital forensics returns trust to digital images
Given the prevalence of current image manipulation and forgery, there is a growing necessity for forensic techniques used to detect digital tampering, according to Dartmouth computer science professor Hany Farid, who is also leader of the Image Science Group at the College.

Farid and his research team have developed a number of methods to identify image manipulation. One technique includes identification of image resampling that examines the pixels of an image for any distinctly algorithmic patterns. Another technique is based on the “color filter array” or “color filter mosaic” property of a camera and can determine whether a questionable area matches the rest of the image’s expected color array.

More recent, cutting edge techniques Farid’s lab has developed include specularity analysis that uses light reflected by the eyes to triangulate where light sources are in an image. Inconsistencies between results could indicate tampering. Given complications with the visibility of eyes in pictures, Farid hopes to expand the technique to all facial features.

“Over the past five years, the field of digital forensics has emerged to help return some trust to digital images,” said Farid. But he acknowledged constant competition between the forgers and authenticators of images. He said, “It’s an arms race.”

Materials Science

CdSe/ZnS quantum dot nanoparticles are surprisingly safe
Commercialized CdSe/ZnS quantum dot nanoparticles are surprisingly not assimilated and most likely nontoxic to aquatic organisms like Daphnia magna, according to research led by Brain Jackson, the director of Dartmouth’s Trace Element Analysis Core Laboratory. The discovery was published in Analytical and Bioanalytical Chemistry.

Quantum dots (QDs) are very small semiconductor particles (< 10 nm) that have unique property of being intensely fluorescent, thus presenting great utility in many markets from optical and electronic applications to medical applications like cellular imaging.

QDs’ small size suggests that they may be easily assimilated by exposed organisms and hence cause toxicity. The research team exposed Daphnia magna to QDs CdSe and ZnS and used synchrotron X-ray fluorescence (SXRF) to study the distribution of zinc (Zn) and selenium (Se) in the organism over a period of 36 hours. The researchers found that there was no evidence of assimilation of QDs in Daphnia.

“We are satisfied with the results. But there is still much to learn about these QDs and our research will continue. A clear understanding of QDs will hold great importance as they become mass produced in the future,” said Jackson.


Spectral karyotype of the human genome.

Spectral karyotype of the human genome.

Mystery of African ancestry and diversity uncovered
Africans are descended from 14 ancestral populations according to Dartmouth Medical School professor Jason Moore and the rest of an international research team led by Sarah Tishkoff of University of Pennsylvania. The finding was published in Science.

The researchers studied genetic variation among 121 African populations, 4 African American populations and 60 non-African populations for patterns of variation. The study showed that Africans originated from fourteen ancestral population clusters that correlate with ethnicity and shared cultural and/or linguistic elements. Further, the data revealed high levels of mixed ancestry in most populations, reflecting historic migration events across the continent.

“In 10 years it will be routine to sequence the entire three billion nucleotides of the genome thus providing all the genetic information for each subject in the study…This data in combination with accurate measures of environmental exposure and analytical approaches that embrace the complexity of the problem is likely to significantly advance our understanding of the genetic basis of common human diseases,” said Moore.

Subglacial microbes from Blood Falls exhibit unique metabolism
Antarctica’s Blood Falls is a mixture of ice, salt crystals, and rust estimated to be 1-1.5 million years old and has been the center of much scientific fascination, including that of Dartmouth earth sciences professor Jill Mikucki, who recently developed a unique theory describing how the metabolic systems of organisms in primitive Earth make life possible. The finding was published in Science.

Organisms living in such anaerobic conditions mostly likely use sulfate or iron rather than oxygen as their final electron acceptor. The main mystery comes from the fact that hydrogen sulfide and Fe (III) typically react to form iron sulfides, such as pyrite; one consequence would be the depletion of Fe (III) so that none could accumulate and no Fe (II) would have the opportunity to form at the surface. Yet plenty of iron flows out of Blood Falls.

Mikucki used isotopes of sulfur and oxygen to track the reactants and products of sulfur compounds in the microbial metabolism. The findings led her to believe that instead of reducing sulfate to hydrogen sulfide like every other known organism, these microbes cut the chain reaction short by facilitating the reduction of Fe (III) to Fe (II). A study of the microbes’ phylogenetic tree reveals a shared evolutionary descent with other anaerobic organisms.

“It’s absolutely incredible how life finds creative pathways to grow even in the most extreme conditions,” said Mikucki.