Diffusion tensor imaging reveals Alzheimer's changes

Jeffrey Prescott from Duke University Medical Center described how changes in white-matter connections could represent an imaging biomarker for Alzheimer's disease. The Duke study looked at the brain's structural connectome, a map of the white-matter tracts that carry signals between different areas of the brain. "The structural connectome provides us with a way to characterize and measure these connections and how they change through disease or age," Prescott explained.

The researchers studied 102 patients enrolled in the Alzheimer's Disease Neuroimaging Initiative who had undergone diffusion tensor imaging (DTI), an MRI technique that assesses the integrity of white-matter tracts in the brain by measuring the diffusion of water molecules. They correlated changes in the structural connectome with results from florbetapir PET, which measures beta-amyloid plaque in the brain. Results showed a strong association between florbetapir uptake (indicating increased amyloid burden) and decrease in strength of the structural connectome, in each of five areas of the brain studied.

"This study ties together two of the major changes in the Alzheimer's brain – structural tissue changes and pathological amyloid-plaque deposition – and suggests a promising role for DTI as a possible diagnostic adjunct," said Prescott. The findings indicate that DTI could play a role in assessing brain damage in early Alzheimer's disease and monitoring the effect of new therapies.

Tomosynthesis improves breast-cancer screening

Digital breast tomosynthesis, or 3D mammography, significantly increases the cancer detection rate when screening women with dense breast tissue, reported Per Skaane from Oslo University Hospital in Norway. Dense breasts, which contain a lot of fibrous or glandular tissue but not much fatty tissue, are more likely to develop cancer, but are also harder to image using mammography. Modalities such as ultrasound and MRI can be used to detect cancers that aren't seen on mammograms, but both exhibit higher rates of false-positive findings.

Skaane and colleagues compared cancer detection rates between full-field digital mammography (FFDM) and FFDM plus digital breast tomosynthesis in 25,547 women. Of the 257 cancers detected overall, 82% were detected with FFDM plus tomosynthesis and 63% with FFDM alone. In women with dense breasts, FFDM plus tomosynthesis pinpointed 80% of the 132 cancer cases, compared with 59% for FFDM alone. The addition of tomosynthesis to FFDM also increased cancer detection for women with fatty breast tissue, from 68% to 84%.

"Our findings are extremely promising, showing an overall relative increase in the cancer detection rate of about 30%," Skaane said. "Stratifying the results on invasive cancers only, the relative increase in cancer detection was about 40%. Tomosynthesis could be regarded as an improvement of mammography and would be much easier than MRI or ultrasound to implement in organized screening programmes."

3D printed models guide human face transplants

Researchers at Brigham and Women's Hospital have studied the impact of using 3D printed models of the patient's head for planning face-transplantation surgery. Physicians at the hospital performed the USA's first full-face transplantation in 2011, and have since completed four additional face transplants. "This is a complex surgery and its success is dependent on surgical planning," said Frank Rybicki, director of the hospital's Applied Imaging Science Laboratory. "Our study demonstrated that if you use this model and hold the skull in your hand, there is no better way to plan the procedure."

Each transplant recipient underwent 3D preoperative CT. To build a life-size skull model, CT images were processed to create input files for a 3D printer. While the entire transplant procedure can last up to 25 hours, creating vascular connections from the donor face to the recipient typically takes about one hour, during which time the patient's blood flow must be stopped. "If there are absent or missing bony structures needed for reconstruction, we can make modifications based on the 3D printed model prior to the actual transplantation, instead of taking the time to do alterations during ischemia time," explained Rybicki.

The researchers also used the 3D models in the operating room, to increase the surgeons' understanding of the anatomy of the recipient's face during the procedure. Senior surgeons and radiologists involved in face transplantations agreed that the 3D printed models provided superior preoperative data and reduced total procedure time. 3D printing is now a mandatory step in surgical planning for face transplantation at Brigham and Women's Hospital, and may be implemented in other complex surgeries in the near future.

PET/CT helps differentiate brain disorders

PET/CT could provide a tool for differentiating military veterans with post-traumatic stress disorder (PTSD) from those with mild traumatic brain injury (mTBI) caused by external force. Differentiating the two conditions can be challenging due to symptom overlap and, in many cases, normal structural neuroimaging results. A study led by Thomas Malone, from Saint Louis University School of Medicine, has evaluated the use of PET/CT to differentiate PTSD from mTBI based on metabolic activity in the pituitary and hypothalamic regions. "The hypothalamic-pituitary-adrenal axis is suspected of playing an important role in PTSD, but there is limited neuroimaging research in the veteran population," said Malone.

The researchers reviewed 159 brain 18F-FDG PET/CT exams from patients with mTBI, mTBI plus PTSD, and normal controls. They found that FDG uptake in the hypothalamus was significantly lower in mTBI-only patients than in the control group, while pituitary gland uptake was significantly higher in the mTBI plus PTSD group compared with the MTBI-only group. The higher FDG uptake seen in the pituitary glands of PTSD sufferers supports the theory that many veterans diagnosed with PTSD may actually have hormonal irregularities due to pituitary gland damage from blast injury. "This raises the possibility that some PTSD cases are actually hypopituitarism," said Malone. "If that's the case, then we might be able to help those patients by screening for hormone irregularities and treating those irregularities on an individual basis."

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