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Current Medical
Imaging Reviews
ISSN: 1573-4056
Current Medical Imaging Reviews
Volume 3, Number 2, May
2007
Contents
Editorial Pp. 77
MRI Techniques for Describing Alterations in
Material Properties of Cartilage and Intervertebral Disc Tissue
Pp. 79-90
Delphine Périé
[Abstract]
Dynamic Contrast Enhanced Magnetic Resonance Imaging
in Oncology: Theory, Data Acquisition, Analysis, and Examples
Pp. 91-107
Thomas E. Yankeelov and John C. Gore
[Abstract]
TMS&fMRI - A New Neuroimaging Combinational Tool
to Study Brain Function Pp. 109-115
Elisabeth de Castro Caparelli
[Abstract]
A Synthesis of Functional Neuroimaging in the Frontal
Variant of Frontotemporal Dementia Pp. 117-121
Eric Salmon, Gaëtan Garraux and Fabienne Collette
[Abstract]
Abnormal Choline Phospholipid Metabolism in Breast
and Ovary Cancer: Molecular Bases for Noninvasive Imaging
Approaches Pp. 123-137
Franca Podo, Francesco Sardanelli, Egidio Iorio, Rossella
Canese, Giulia Carpinelli, Alfonso Fausto and Silvana Canevari
[Abstract]
Measurement of Cerebral Blood Flow with Near Infrared
Spectroscopy and Indocyanine Green Dye Dilution Pp.
139-150
Emanuela Keller and Regina Mudra
[Abstract]
Abstracts
[Back to top]
Editorial: Advanced MRI, MR as well as Optical
Spectroscopy
The last quarter century has witnessed the introduction
of a variety of powerful techniques that have allowed visualization
of organ structure and function with exquisite detail. This
in turn has brought about a true revolution in the day-to-day
practice of medicine. There are six articles in this issue,
related to the MRI for cartilage and disc, oncology, brain
function and dementia, the MR spectroscopy for breast and
ovary cancer, and the optical spectroscopy for cerebral blood
flow.
Although MRI has become the most accurate test for depicting
abnormal anatomy, there is no agreement on the diagnostic
value of morphology alone. If the natural history of a disease
is not clearly understood, and if there is little consensus
regarding the use of diagnostic tests, the risk of misdiagnosis
is high. Degenerative disc disease is debilitating, costly,
and one of the most complex conditions to manage. MRI has
demonstrated alterations in material properties (mainly glycosamineoglycans,
water and collagen) of hydrated cartilages and also intervertebral
disc tissues during the disease developments. The long term
goal would develop techniques to detect changes of early degeneration
of cartilages and discs. It was found that contrast-enhanced
MRI improved lesion detection, delineation, and specificity.
The major factors influencing lesion detection include lesion
contrast, size, location, and type. Dynamic contrast enhanced
MRI (DCE-MRI) enables the quantitative assessment of tumor
status using blood flow, vessel permeability, and tissue volume
fractions extracted from each voxel or region of interest.
Functional MRI has been widely used to evaluate brain response
for extensive number of different tasks, and primarily intended
for the assessment of physiologic phenomena, such as changes
in blood flow and perfusion to an organ or diseased tissue.
I remains unclear which brain region is relevant for the principal
cognitive/behavioral function and which areas are activated
either ws a result of the additional cognitive function or
as consequence of brainconnectivity. The recent conbination
of transcranial magnetic stimulation and functional MRI has
shown to be a promising tool to clarify this dilemma.
With the current trend towards increasing longevity of life,
the prevalence of dementia will become higher during the next
few decades. Dementic illness imposes significant burdens
on the society, health care and economy. Neurochemical imaging
is one of the most established molecular imaging technique.
There have been tremendous efforts to develop radioligands
specific to each neurochemical system. Investigational applications
of neurochemical imaging indementing disorders are extensive.
These investigations have provided important insights into
disease processes inliving human patients. Frontotemporal
decrease of the activity on functional imaging is an independent
marker of the frontal variant of frontotemporal dementia.
MR spectroscopy (MRS) is increasingly receiving more attention
from oncologists, neuropsychiatrists, radiologists, and other
clinicians. The choline peak from proton spectra is a constitution
of the phospholipids metabolism of cell membrane and thus
reflects a membrane turnover. It is a precursor of acetylcholine
and phosphatidylcholine and therefore increased choline probably
suggests increased membrane synthesis or an increased number
of cells such as seen in active tumors. Efforts are addressed
to evaluate effectiveness and potential use of MRS and choline-based
PET in cancer diagnosis.
Optical imaging is a very powerful molecular imaging probe,
but it does not lend itself well to examining biologic processes.
Tradionally it has had physiological limitations in visualizing
deel structures or lesions. However, new-generation near infrared
spectroscopy (NIRS) instrumentation with depth-resolved technologies
and invasive NIRS probes will provide unique physiologic informations
including cerebral blood flow.
Dr. E. Edmund Kim
(Editor-in-Chief)
Division of Diagnostic Imaging
The University of Texas M.D.
Anderson Cancer Center
Box59, 1515 Holcombe Blvd
Houston, TX 77030-4009
USA
Email: ekim@di.mdacc.tmc.edu
[Back to top]
MRI Techniques for Describing Alterations
in Material Properties of Cartilage and Intervertebral Disc
Tissue
Delphine Périé
The aim of this review is to present the different stages,
from geometrical to mechanical data, in the development of
sensitive and non-invasive MRI techniques for describing alterations
in material properties of cartilage and intervertebral disc
tissue with disease.
The first section summarizes some MRI techniques used to quantify
the geometrical changes in cartilage and intervertebral disc
tissue that appears with diurnal activity, specific movements
or loadings, or else with various diseases. The second section
describes the MRI techniques used to evaluate the biochemical
composition of cartilage and intervertebral disc tissue, mainly
the glycosaminoglycans (GAGs) and water contents, and the
collagen organization. The third section describes the MRI
techniques used to quantify the mechanical and structural
properties of bone tissue. The last section presents the new
MRI techniques used to evaluate the mechanical properties
of hydrated cartilage and intervertebral disc tissue.
More studies highlighting the ability of MRI to describe the
fluid phase behavior within the cartilage or intervertebral
discs tissue should be perform. The long term goal would be
to develop sensitive and non-invasive clinical techniques
for the early detection of the changes in the mechanical properties
of both solid and fluid phases that appear with degeneration.
[Back to top]
Dynamic Contrast Enhanced Magnetic Resonance Imaging
in Oncology: Theory, Data Acquisition, Analysis, and Examples
Thomas E. Yankeelov and John C. Gore
Dynamic contrast enhanced MRI (DCE-MRI) enables the quantitative
assessment of tumor status and has found application in both
pre-clinical tumor models as well as clinical oncology. DCE-MRI
requires the serial acquisition of images before and after
the injection of a paramagnetic contrast agent so that the
variation of MR signal intensity with time can be recorded
for each image voxel. As the agent enters into a tissue, it
changes the MR signal intensity from the tissue to a degree
that depends on the local concentration. After the agent is
transported out of the tissue, the MR signal intensity returns
to its’ baseline value. By analyzing the associated
signal intensity time course using an appropriate mathematical
model, physiological parameters related to blood flow, vessel
permeability, and tissue volume fractions can be extracted
for each voxel or region of interest.
In this review we first discuss the basic physics of this
methodology, and then present technical aspects of how DCE-MRI
data are acquired and analyzed. We also discuss appropriate
models of contrast agent kinetics and how these can be used
to elucidate tissue characteristics of importance in cancer
biology. We conclude by briefly summarizing some future goals
and demands of DCE-MRI.
[Back to top]
TMS&fMRI - A New Neuroimaging Combinational Tool
to Study Brain Function
Elisabeth de Castro Caparelli
Functional magnetic resonance imaging (fMRI) has been widely
used to evaluate the brain’s response to an extensive
variety and number of different tasks; however, because many
of these paradigms are complex, they stimulate a broad neural
network encompassing several brain regions. Therefore, it
remains unclear which brain region is relevant to the principal
cognitive/behavioral function that is being studied, and which
areas are activated either due to the additional cognitive
function required to complete the task, or as a consequence
of brain connectivity. The recent combination of transcranial
magnetic stimulation (TMS) with fMRI holds promise for clarifying
this dilemma. Using a pulse of magnetic field, TMS can non-invasively
stimulate a specific brain region, thereby allowing brain
activity to be manipulated as an independent variable, while,
based upon the Blood Oxygenation Level Dependence (the BOLD
effect), fMRI can evaluate the brain’s response to this
localized stimulus, highlighting the functional network directly
associated with the stimulated site.
[Back to top]
A Synthesis of Functional Neuroimaging in the Frontal
Variant of Frontotemporal Dementia
Eric Salmon, Gaëtan Garraux and Fabienne Collette
The frontal variant of frontotemporal dementia (fvFTD) is
clinically characterized by a disruption of the social behaviour.
Frontotemporal decrease of activity on functional imaging
is an independent marker of the disease. Principal component
analysis of cerebral functional images reveals one ensemble
comprising both frontal lobes, and two lateralized clusters
comprising temporal and subcallosal frontal regions. Executive
dysfunction and verbal difficulties are shown to interact
in fvFTD, and they are related to large scale frontal and
temporal neural networks in the disease. The neural substrate
of the memory impairments in patients with fvFTD is heterogeneous,
since correlations were observed with frontal activity, but
also with medial temporal atrophy. Behavioural changes are
the hallmarks of fvFTD. Apathy is consistently related to
frontal involvement, while disinhibition occurs in patients
with predominant posterior orbitofrontal and temporal involvement.
The consequences of lateralized brain lesions remain a matter
of debate, since impulsive and compulsive behaviour was evenly
related to right or left temporal involvement in fvFTD. Those
patients know social rules, but they are impaired in assessing
the importance of social transgressions and in recognizing
emotions. Processing transgressions of social norms results
in a complex activation of medial prefrontal, orbitofrontal
and temporal regions in control populations. The variable
decrease in these regional activities observed in different
fvFTD patients would explain their complex, individual social
disturbance.
[Back to top]
Abnormal Choline Phospholipid Metabolism in Breast
and Ovary Cancer: Molecular Bases for Noninvasive Imaging
Approaches
Franca Podo, Francesco Sardanelli, Egidio Iorio, Rossella
Canese, Giulia Carpinelli, Alfonso Fausto and Silvana Canevari
Elevated contents of choline phospholipid metabolites are
typically detected by nuclear magnetic resonance spectroscopy
(MRS) in human and animal tumors. An increase in the intensity
of the 1H MRS profile of
total choline-containing compounds (tCho, 3.2 ppm) is today
considered as a common feature in different types of cancer,
beyond their otherwise wide phenotypic variability. This finding
fostered investigations on the molecular mechanisms underlying
the observed spectral changes and on correlations between
aberrant phospholipid metabolism and tumor progression. At
the clinical level, efforts are addressed to evaluate effectiveness
and potential use of in vivo localized MRS and choline-based
positron emission tomography (Cho-PET) in cancer diagnosis.
Aims of this article are: a) to overview recent advances in
the identification of biochemical pathways responsible for
the altered 1H MRS tCho profile
in breast and ovary cancer cells, as a basis for interpreting
in vivo MR spectra and enhanced uptake of radiolabeled
choline in PET; b) to summarize recent developments of in
vivo 1H MRS methods
in breast cancer diagnosis; c) to discuss the potentialities
of complementing current diagnostic modalities with noninvasive
MRS and Cho PET methods to monitor biochemical alterations
associated with progression, relapse and therapy response
in ovary cancer.
[Back to top]
Measurement of Cerebral Blood Flow with Near Infrared
Spectroscopy and Indocyanine Green Dye Dilution
Emanuela Keller and Regina Mudra
Early detection and treatment of cerebral ischemia to prevent
further neurological damage in patients with severe brain
injuries, such as in trauma and stroke patients, is one of
the most important issues in Neurocritical Care. Our own clinical
experiences in treatment of patients with severe ischemic
stroke and subarachnoid hemorrhage have shown that the available
methods to monitor cerebral hemodynamics and oxygenation are
insufficient with regard to detection of secondary ischemic
events. The established methods for bedside monitoring of
cerebral blood flow (CBF) and cerebral oxygenation are difficult
to perform clinically, involve radioactive radiation, are
invasive or require the patient to be transported, thus involving
potentially high risks. Transcranial Doppler sonography produces
indices that can be related to changes in CBF and cerebral
oxygenation but does not measure actual flow rates.
During recent years, near infrared spectroscopy (NIRS) was
further developed and supplemented with the indocyanine green
(ICG) dye dilution mode for bedside monitoring of CBF. The
NIRS ICG dye dilution technique is a promising method for
serial bedside CBF measurements in the environment of the
intensive care unit. The NIRS method with optodes on the skin
has the advantage of being non invasive, does not require
the patient to be transported and provides data at the bedside
within minutes.
Preliminary data in a limited number of volunteers indicate
that CBF measurements obtained by NIRS ICG dye dilution technique
are in agreement with corresponding values obtained by perfusion-weighted
MRI. More patient-validated data by correlating the measurement
values with clinical events and comparing them with standard
methods are needed. For the accuracy of absolute measurements
and in order to quantify the individual extracerebral pathlengths
as well as to allow appropriate correction to be made for
extracerebral dead space tissue further modelling based on
patients data is required.
New-generation NIRS instrumentation, implementing spatially
resolved spectroscopy (SRS), depth-resolved technologies and
invasive NIRS probes will give the opportunity to reduce or
eliminate extracerebral contamination and will provide some
unique physiological information for NIRS technology. To calculate
the influence of extracerebral contamination comparative measurements
can be performed using noninvasive NIRS probes on the scalp
and invasive probes for NIRS and intracranial pressure (ICP)
monitoring. Combined monitoring of ICP and NIRS will be of
special clinical value in patients with severe stroke, subarachnoid
hemorrhage and head trauma, already provided with ICP probes
for treatment of intracranial hypertension and being especially
at risk for secondary ischemic brain damage.
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