The WCC Note

Your Weekly Guide to Harmonizing Clinical Trial Imaging

Posts Tagged ‘CT’

Real-Time Imaging, MRI & CT Photography, and MRI: Accurate Temperature – Vol. 2, Number 26

Tuesday, November 11th, 2008

REAL-TIME IMAGING

Dynamic Imaging of Cells Accompanying Cancer Achieved in Mice
Neoplasms contain a microenvironment of multiple other cell types that exist alongside the carcinoma cells.  Termed stromal cells, they include such cells as fibroblasts, lymphocytes, dendritic cells, and macrophages.  These elements combine with extracellular factors, such as growth factor collagen, and oxygen, to form a milieu that evolves along with the carcinoma cells and influences tumor growth.  A recent study sought to image and assess these parallel elements, with the authors developing and using multicolor imaging techniques within a live mouse.  As published in Disease Models & Mechanisms and reported in Science, the authors described designing a spinning disk confocal microscope that achieved image acquisition times of 17 and 33 milliseconds for 512 x 512 and 1024 x 1024 pixel images, respectively.  Led by researchers from the University of California, San Francisco, the study typically collected 32,400 images in a 12-hour period, then documented the location and movement of stromal cells and oxygen’s effect upon them.

Conclusion:  A novel in vivo imaging technique affords high-resolution, four-color, prolonged, real-time imaging of cells that accompany cancer.

MRI & CT PHOTOGRAPHY

Radiologist Wins Lennart Nilsson Award for Scientific PhotographyChimp-3d-photo
The journal Nature recently reported that radiologist Anders Persson of Sweden has won the Lennart Nilsson Award for scientific photography, citing his stunning computer-enhanced 3D images made using new techniques in MRI and CT.  Der. Persson was quoted as saying that technical research should benefit the patient, and that he wanted to show precise and colorful details to achieve that end.  He discussed the utility of imaging in forensic medicine, including the performance of virtual autopsies.  Such post-mortem exams can allow discovery of facts not appreciable in conventional autopsies, such as gas in wounds or small metal particles under the skin.  Persson is currently working on several new facets of medical imaging, including multi-energy CT to visualize the body’s chemical constitution.

Conclusion:  The Lennart Nilsson Award for scientific photography has been awarded to Swedish radiologist Anders Persson.

MRI: ACCURATE TEMPERATURE

MRI Pulsing Sequences Yield Accurate Temperature Imaging
Temperature plays an integral role in medicine.  Its change can reflect metabolism, immune function, and cancer.  For example, digital infared thermal imaging for breast cancer detection was recently reported to show high sensitivity and negative predictive value, depending on the method used.  The current and developing arsenal of various disease therapies includes hyperthermic treatments and thermally sensitive agents that can selectively release drugs based on heat range.  Noting that temperature is a fundamental quality of matter that proves extremely difficult to measure noninvasively below an object’s surface, researchers sought to image it in a broad range of environments with magnetic resonance.  As reported recently in Science, researchers at Princeton and Duke Universities have reported accurate temperature imaging with MRI, using a new pulsing method, and obtained in vivo mouse images.

Conclusion:  Newly developed MRI pulsing sequences can achieve rapid and accurate internal temperature images.

MRI: Brain & Contrast and Cardiac CT – Vol. 2, Number 22

Thursday, September 4th, 2008

MRI: BRAIN

Imaging Reveals Astrocytes Can Respond to Visual Stimuli
Neurons are known as the principal functioning cells in the brain, receiving, storing, and transmitting information.  Higher-order functions such as sight, therefore, rely on neurons.  The brain’s star-shaped astrocyte cells are thought to perform functions for neurons, metabolically buffering, detoxifying, supplying nutrients, and electrically insulating them.  Astrocytes also contribute to brain barriers and play a principal role in brain repair and brain scar formation.  Until now, the ability to see had not been a role ascribed (in part) to astrocytes.  Yet researchers at the Massachusetts Institute of Technology recently documented that astrocytes do indeed respond to visual stimuli.  The authors used two-photon imaging of calcium signals in vivo, employing a ferret visual cortex model.  As reported in Science, astrocytes displayed distinct spatial receptive fields, as well as orientation and spatial associations.  The finding suggests the role of both neurons and astrocytes in vision.  This holds implications for non-invasive imaging techniques that study brain activity, such as functional MRI.

Conclusion:  Imaging shows that astrocytes join neurons as cells known to respond to visual stimuli.

MRI: CONTRAST

Alternative MRI Contrast Agent Can Deliver Therapeutic Drugs
Gadolinium has dominated the MRI contrast market since it was approved for human use 20 years ago.  More than 85 million doese had been administered by 2007, about 5 million annually.  A recent study in the Journal of the American Chemical Society reports the creation of a novel MRI contrast agent that is not gadolinium-based, but rather manganese-labeled, toroidal (doughnut-shaped) nanoparticles.  This new molecular agent can target fibrin, a constituent of a clot.  The authors, from Washington University School of Medicine, Philips HealthCare, and St. Thomas Hospital (London), state that the agent can also incorporate chemotherapeutic compounds, raising the possibility of its exhibiting both diagnostic and therapeutic utilities.

Conclusion:  A novel MRI contrast agent can not only target the fibrin in thrombus, but also deliver therapeutic compounds.

CARDIAC CT

Pericardial Fat Is Related to Calcified Coronary Artery Plaque
The U.S. Centers for Disease Control (CDC) report that an estimated 66 percent of U.S. adults and 17 percent of children and adolscents are overweight.  Inflammatory cytokines exist at higher levels in pericardial fat than in subcutaneous fat.  To assess whether pericardial fat is associated with calcified coronary artery plaque, researchers for the Multiethnic Study of Atherosclerosis examined the volume of pericardial fat on cardiac CT in 159 patients in Forsythe County, NC, and evaluated for calcified coronary artery plaque.  As reported in the research journal Obesity, pericardial fat proved significantly associated with calcified coronary artery plaque, even when adjusting for other cardiovascular risk factors, and was independent of gender and ethnicity.

Conclusion:  Pericardial fat is associated with calcified coronary artery plaque, independent of gender and ethnicity.

CCTA and MRI: Fibromyalgia & Pancreatic Cancer
Vol. 2, Number 18

Tuesday, July 8th, 2008

MRI: FIBROMYALGIA

Fibromyalgia Patients Demonstrate Different Brain Metabolite Levels on Proton MR Spectroscopy
A study from the University of Michigan investigated brain metabolite differences between people with fibromyalgia (FM) and healthy controls (HC).  The authors sought to test the hypothesis that the broad pain sensitivity experienced by fibromyalgia patients related to a central nervous system processing problem, which would therefore display metabolic alteration in those brain areas involved in processing pain.  Published in the American Journal of Neuroradiology in May 2008, the study examined 21 patients with FM and 27 controls.

Conventional MR was supplemented with 2D-chemical shift imaging (CSI) MR-spectroscopy.  The spectroscopy centered at the basal ganglia and supraventricular white matter.  Within these regions, the study interrogated the spectrographic features of smaller areas implicated in pain processing.  The authors calculated the N-acetylaspartate (NAA)/creatine (Cr), choline (Cho)/Cr, and NAA/Cho ratios for each voxel.  They also performed clinical and experimental pain assessments on all the subjects.  The Cho/Cr variability in the right dorsolateral prefrontal cortex proved significantly different in patients with fibromyalgia as compared to controls.  NAA/Cho ratios in the left insula and left basal ganglia showed significant correlations with evoked pain threshold.

Conclusion:  Patients with fibromyalgia demonstrate baseline brain metabolite variability differences compared to health controls.  Those with fibromyalgia also show significant correlation between metabolite ratios and pain parameters.

MRI: PANCREATIC CANCER

Targeted Nanoparticles Image Small Pancreatic Cancers and Cancer Precursor Lesions in Mice
Pancreatic cancer typically eludes detection until the tumor ha reached an incurable state.  In an effort to discover small cancers and precursor lesions that may be curable, researchers at the Massachusetts General Hospital and Dana Farber Cancer Institute developed a novel imaging approach.  The technique exploits the cancer cells’ mutations, which cause different cell-surface proteins to be present than in normal cells.  After detecting several peptides bound to the outside of pancreatic cancer cells but absent on normal cells, an imaging probe was created to make use of this difference.

As reported online in April 2008 by the Public Library of Science, the researchers next found a virus phage clone that bound to these mouse tumor cell peptides.  To accomplish imaging the lesions, the investigators then linked the phages to nanoparticles that had both magnetic and fluorescent properties.  Using mouse models, the nanoparticles allowed detection of small pancreatic ductal carcinomas and precursor lesions.

Conclusion:  The imaging of small and precursor pancreatic adenocarcinomas in mice was accomplished by using nanoparticles linked to viral phages which, in turn, bind to pancreatic carcinoma sell surface peptides.  If the approach can be successfully translated for use in humans, some tumors heretofore typically diagnosed when already incurable could be discovered earlier.

CCTA

Dual-Source Coronary Artery CT Angiography Promising for Atrial Fibrillation Patients
Currently, coronary artery computed tomographic angiography (CCTA) technique relies on imaging the vasculature in the setting of a slow heart rate with regular rhythm.  When tachycardia or irregular beats occur during imaging, image blurring may preclude a diagnostic evaluation of the coronary arteries.  Patients with atrial fibrillation are therefore contraindicated, because faster scanner times than those available with 64-slice, multi-detector scanners would be required.

Authors from Cedars-Sinai Medical Center and University of California-Los Angeles examined dual-source CT (DSCT) for coronary evaluation in 24 patietns with atrial fibrillation (AF) and compared it to 119 control patients in sinus rhythm.  The patients underwent B-blockade to achieve heart rates of 65 beats per minute or less and were also given nitroglycerin.  Bolus tracking was employed with retrospective ECG-gating.  The control group underwent tube current modulation; this was not used in the AF patients to maximize the visualization of all phases of the cardiac cycle.  Patients in both groups had similar coronary calcium scores and prevalence of coronary artery disease.  In the atrial fibrillation group, 2 (8%) of studies proved nondiagnostic, compared to 12 (10%) of the nondiagnostic control group exams.

Conclusion:  Atrial fibrillation patients may be able to undergo diagnostic CCTA in dual-source CT scanners.

Radiology: The Basic Modalities
Radiation Exposure – Vol. 1, Number 2

Tuesday, October 2nd, 2007

What it is, what it does. It’s widely known today that radiation can be harmful to humans.  The effects of large amounts of radiation, as seen in radiation therapy for cancer or among the fallout victims of Chernobyl or Hiroshima, are almost immediate and quite apparent.  However, it can be difficult to quantify the amount of damage from the smaller amounts of radiation used in diagnostic radiology, as these are the cumulative effects that are only seen many years after exposure and thus cannot be linked to the radiographic study.
The documented efforts of radiation have to do with the “ionization” of a cell.  That is, when an x-ray hits a cell, it causes the electrons to displace, damaging the cell’s function.  Although the cell may repair itself, it may not do so completely, and thus loses its ability to function normally.  The DNA within the cell also may be damaged, leading to cell death or other mutation.

HOW IS RADIATION MEASURED?

Many units are used to measure radiation dosage.  The unite used in the measurements below is called the “sievert,” a measure of the amount of radiation absorbed by the human body.

Effective Radiation Dosage (in MilliSieverts):
Average background dose in the U.S. . . . . . . . . . 3.6 mSv/year
Three-hour commercial airline flight. . . . . . . . . . 0.015 mSv
Chest X-ray (two views). . . . . . . . . . . . . . . . . . . . . 0.05 mSv
Head CT scan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 mSv
Chest CT scan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 mSv
Abdomen and pelvis CT scan. . . . . . . . . . . . . . . . . 6-8 mSv
Selective diagnostic coronary angiography. . . . 3-6 mSv
Coronary CT angiography. . . . . . . . . . . . . . . . . . . 8-13 mSv

SOME RADIATION RISK FACTORS

Although exact risk levels from radiation in diagnostic imaging are difficult to quantify, we now know that the impact of radiation on a live subject or patient depends on many factors, including:

  • Patient age
    - The younger the subject, the greater the risk to an exposed cell
  • The organ affected
    - The ovaries and eyes, for example, are very radiation-sensitive, while the heart and brain are very radiation-resistant
  • The body region imaged
    - A CT scan of the pelvis causes more damaging radiation than a CT scan of the head, because the pelvis contains many radiation-sensitive organs
  • Cumulative dose
    - A certain amount of radiation delivered all at once (an acute dose) is more damaging than spreading that radiation out over a longer time
    - Even if small doses of radiation are delivered at different times (such as two abdominal x-rays done a week apart), the dose accumulates to cause an increased risk of adverse effects
    - Less radiation is ALWAYS better
  • A patient’s genetically inherent resistance to radiation