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Current Medical
Imaging Reviews
ISSN: 1573-4056
Current Medical Imaging Reviews
Volume 2, Number 1, February
2006
Contents
Editorial Pp. 1
The New Challenges of Brain PET Imaging Technology
Pp. 3-13
Habib Zaidi and Marie-Louise Montandon
[Abstract] [Purchase
Issue/Articles]
Models of Functional Neuroimaging Data Pp.
15-34
Klaas Enno Stephan, Jeremie Mattout, Olivier
David and Karl J. Friston
[Abstract] [Purchase
Issue/Articles]
Functional Neuroimaging in Memory and Memory Disturbances
Pp. 35-57
Nadine Reinhold, Sina Kuehnel, Matthias Brand
and Hans J. Markowitsch
[Abstract] [Purchase
Issue/Articles]
Contributions of Functional Neuroimaging to Clinical
and Cognitive Neuropsychology: A Selective Review Pp.
59-69
Sylvie Chokron
[Abstract] [Purchase
Issue/Articles]
Neuroimaging Techniques as a New Tool to Study the
Neural Correlates Involved in Human Male Sexual Arousal Pp.
71-77
Harold Mouras
[Abstract] [Purchase
Issue/Articles]
Magnetic Resonance Imaging of Short T2 Relaxation
Components in Tissue Using Ultrashort Echo Time (UTE) Pulse
Sequences Pp. 79-90
Mark Bydder, Richard M. Znamirowski and Graeme
M. Bydder
[Abstract] [Purchase
Issue/Articles]
Current Methods in the Automatic Tissue Segmentation
of 3D Magnetic Resonance Brain Images Pp. 91-103
Alan Wee-Chung Liew and Hong Yan
[Abstract] [Purchase
Issue/Articles]
Longitudinal Functional MRI of Motor and Cognitive
Recovery Following Stroke: A Review Pp. 105-116
Erin A. Douglas, Jodi D. Edwards and Bradley
G. Goodyear
[Abstract] [Purchase
Issue/Articles]
From Cerebrospinal Fluid Pulsation to Noninvasive
Intracranial Compliance and Pressure Measured by MRI Flow
Studies Pp. 117-129
Noam Alperin, Monica Mazda, Terry Lichtor and Sang H. Lee
[Abstract] [Purchase
Issue/Articles]
Gradients: The Heart of the MRI Machine Pp.
131-138
Barry L.W. Chapman
[Abstract] [Purchase
Issue/Articles]
Clinical Applications of Cardiac Multi-Slice Computed
Tomography Pp. 139-146
Joanne D. Schuijf, Monique R.M. Jongbloed, Wouter J. Jukema,
Hildo J. Lamb , Ernst E. van der Wall, Albert de Roos and
Jeroen J. Bax
[Abstract] [Purchase
Issue/Articles]
Peripheral Vascular Disease: The Role of MR- Angiography
Pp. 147-155
Nikolaos Economopoulos, Elias N. Brountzos and Nikolaos
L. Kelekis
[Abstract] [Purchase
Issue/Articles]
Ultrasonic Elasticity Imaging as a Tool for Breast
Cancer Diagnosis and Research Pp. 157-164
Claire Pellot-Barakat, Mallika Sridhar, Karen
K. Lindfors and Michael F. Insana
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Abstracts
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Editorial
Two observations emerge from a review of the articles
contained in this issue of CMIR. The first and perhaps most
important is the remarkable growth in diagnostic technology.
PET imaging has increased in utilization during the past several
years so that it is now a part of the state-of-the-art of
cancer care. The increased availability of combined PET/CT
imaging has greatly fostered its growth and increased the
specificity and accuracy of the technology. During the same
time interval, faster and faster multi slice computed tomography
devices have become available so that at the present time
a 16 slice CT machine is pretty much the state-of-the-art,
with 32 slice machines moving into the clinical area and 64
slice machines not far behind. The ultimate cardiac approach
on the horizon appears to be the combination of a 64 slice
CT with a PET machine so that patients would be able to have
non-invasive coronary angiography performed at the same sitting
with physiologic studies demonstrating perfusion and leading
to decisions regarding cardiac intervention with no need for
a cardiac cath. Of course, as this technology becomes more
and more refined, there is an unavoidable increase in the
cost of medical diagnosis. We have yet to learn the balance
between physical examination, imaging technology and patient
care. Unfortunately too many physicians move quickly to diagnostic
studies without a careful intervening medical history and
physical examination.
That said, the other observation is that in this issue, which
contains 13 articles, 8 are directly related to studies of
the brain. It is remarkable that although a remarkable amount
of work has been directed towards the study of the brain utilizing
CT, MRI, and PET, the roles of these modalities in clinical
medicine do not reflect volume of physiologic research. MR
and CT have certainly become standard techniques for evaluating
the brain but as demonstrated in these articles much of the
information derived is still in the research sphere. Even
more impressive is the general lack of utilization of PET
in studies of brain disease while it has played a profound
role in defining diseases such as Alzheimer’s disease,
multi infarct dementia, and other serious brain afflictions.
It is evident from a review of these articles that diagnostic
technology is improving at a logarithmic rate. It is also
evident from the large number of research publications in
the various areas that the movement from the laboratory to
clinical medicine continues to lag. We are faced with an explosive
growth in diagnostic methodology during the next decade. How
this will impact on financing of medical care and on the algorithms
for diagnosis of disease is something that will be a painful
evolution both politically and economically based with a revolution
medically and scientifically.
M. Donald Blaufox M.D., Ph.D.
Department of Nuclear Medicine
Albert Einstein College of Medicine
and Montefiore Medical Center
1695A Eastchester Road
Bronx, New York 10461
USA
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The New Challenges of Brain PET Imaging Technology
Habib Zaidi and Marie-Louise Montandon
During the last two decades, functional brain imaging using
positron emission tomography (PET) has advanced elegantly,
and steadily gained importance in the clinical and research
arenas. Significant progress has been made by different scanner
manufacturers and research groups in the design of dedicated
high-resolution three-dimensional (3-D) PET units; however,
emerging clinical and research applications of functional
brain imaging promise even greater levels of accuracy and
precision and therefore, impose more constraints with respect
to the intrinsic performance of the PET tomograph. Continuous
efforts to integrate recent research findings for the design
of different geometries and various detector/readout technologies
of PET scanners have become the goal of both the academic
community and nuclear medicine industry. As PET has become
integrated into clinical practice, several design trends have
developed; with systems now available with a spectrum of features,
from those designed for "low cost" clinical applications
to others designed specifically for very high-resolution research
applications. There is also a continual upward revision and
refinement in both hardware and software components for all
of these systems.
Software- and hardware-based correlation between anatomical
(x-ray CT, MRI) and physiological (PET) information is a promising
research field and now offers unique capabilities for the
medical imaging community and biomedical researchers. One
of the main advantages of dual-modality PET/CT imaging is
that PET data are intrinsically aligned to anatomical information
from the x-ray CT without the use of external markers or internal
landmarks, thus providing a reliable estimate of the attenuation
map to be used for attenuation and scatter correction purposes.
On the other hand, combining PET with MRI technology is scientifically
more challenging owing to the strong magnetic fields. Nevertheless,
significant progress has been made resulting in the design
of a prototype small animal PET scanner coupled to three multi-channel
photomultipliers via optical fibers, so that the PET detector
can be operated within a conventional MR system. Thus, many
different design paths have been and continue to be pursued
in both academic and corporate settings, that offer different
trade-offs in terms of their performance. It still is uncertain
which designs will be incorporated into future clinical and
research systems, but it is certain that technological advances
will continue and will enable new quantitative capabilities
in brain PET imaging. This paper briefly summarizes state
of the art developments in dedicated brain PET instrumentation.
Future prospects will also be discussed.
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Models of Functional Neuroimaging Data
Klaas Enno Stephan, Jeremie Mattout, Olivier
David and Karl J. Friston
Inferences about brain function, using functional neuroimaging
data, require models of how the data were derived. A variety
of models are used in practice that range from conceptual
models of functional anatomy to nonlinear mathematical models
of hemodynamic responses (e.g. as measured by functional magnetic
resonance imaging, fMRI) and neuronal responses. In this review,
we discuss the most important models used to analyse functional
imaging data and demonstrate how they are interrelated. Initially,
we briefly review the anatomical foundations of current theories
of brain function on which all mathematical models rest. We
then introduce some basic statistical models (e.g. the general
linear model) used for making classical (i.e. frequentist)
and Bayesian inferences about where neuronal responses
are expressed. The more challenging question, how
these responses are caused, is addressed by models that incorporate
biophysical constraints (e.g. forward models from the neural
to the hemodynamic level) and/or consider causal interactions
between several regions, i.e. models of effective connectivity.
Some of the most refined models to date are neuronal mass
models of electroencephalographic (EEG) responses. These models
enable mechanistic inferences about how evoked responses are
caused, at the level of neuronal subpopulations and the coupling
among them.
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Functional Neuroimaging in Memory and Memory Disturbances
Nadine Reinhold, Sina Kuehnel, Matthias Brand
and Hans J. Markowitsch
During the past years brain imaging techniques like positron
emission tomography (PET) and functional magnetic resonance
imaging (fMRI) became more and more important for gaining
new insights into processes of and circuits for memory encoding
and retrieval. These findings also had a great impact on a
better understanding of memory dysfunctions and their underlying
brain mechanisms. In the present review, data on memory dysfunctions
are analyzed separately according to whether they are of an
organic, or a psychiatric psychogenic etiology. Studies examining
patients with various forms of amnesia and dementia, for whom
functional brain imaging data were available, indicate early
functional brain changes. These early changes differ from
subsequent structural brain changes and therefore support
the clinical and diagnostic use of functional brain imaging
techniques in memory disturbances. Furthermore, research outcomes
from patients suffering from psychogenic amnesias (dissociative
amnesias) and psychogenic fugue conditions are summarized.
Finally, differences and similarities between organic amnesia
and psychogenic amnesia are discussed with regard to the present
literature and exemplified with two single cases from our
lab.
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Contributions of Functional Neuroimaging to Clinical
and Cognitive Neuropsychology: A Selective Review
Sylvie Chokron
Functional neuroimaging has provided a new view of the activity
in the human cortex. The understanding of the relationship
between functional signals, particularly functional MRI, clinical
disorders and cognitive functions has increased. This article
reviews selected contributions of positron emission tomography
(PET), functional magnetic resonance imaging (fMRI) and transcranial
magnetic stimulation (TMS) with a focus on their interest
to better understand visual cognition, hemispheric specialization,
and cerebral plasticity. Future directions of functional neuroimaging
research are proposed, with the emphasis that the most complete
conclusions are drawn by convergence of research from functional
neuroimaging, neurophysiological, and lesion studies. We also
briefly mention the emerging role of TMS, as a tool to simulate,
study and understand the dynamic course of deficits observed
after a cortical lesion in ‘virtual neuropsychology’.
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Neuroimaging Tech niques as a New Tool to Study the
Neural Correlates Involved in Human Male Sexual Arousal
Harold Mouras
During the last five years, neuroimaging techniques such
as Positron Emission Tomography (PET) and functional Magnetic
Resonance Imaging (fMRI) appeared as new tools to study the
neural correlates of human male sexual arousal (SA). In this
paper, some of the main methodological aspects of these studies
will be summarized, including the participants, the way to
induce sexual arousal within the scanner and the different
types of analyses performed. In the second part, some of the
cerebral areas that have been related to sexual information
processing are presented. Among others, cerebral areas that
have been related to cognitive processes involved in SA are
first presented: the orbitofrontal cortex and parietal lobules.
We then focus on recent studies that concurrently measured
cerebral and penile responses by plethysmography. Some cerebral
areas where significant correlations were found between the
hemodynamic cerebral and the plethysmographic signals are
presented. Finally, as the use of different penile plethysmographic
methods were referred to in the literature, we consider the
prospects of their use for the study of the neural correlates
of human male SA.
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Magnetic Resonance Imaging of Short T2 Relaxation
Components in Tissue Using Ultrashort Echo Time (UTE) Pulse
Sequences
Mark Bydder, Richard M. Znamirowski and Graeme
M. Bydder
The clinical use of ultrashort echo time (UTE) pulse sequences
for imaging tissues or tissue relaxation components with short
T2s is described. Tissues are divided into those
with a majority of short T2 components and those
with a minority. Disease processes which increase or decrease
the signal from short T2 components are described.
Features of the basic physics are described including the
fact that when the radiofrequency pulse duration is of the
order of T2, rotation of tissue magnetization less
than the specified flip angle. The basic UTE pulse sequence
with its half excitation pulses and radial imaging from the
center of k-space is described together with options that
suppress fat and/or long T2 components. Features
of the imaging of cortical bone, tendons, ligaments, menisci
and periosteum are illustrated. Possible future developments
are outlined.
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Current Methods in the Automatic Tissue Segmentation
of 3D Magnetic Resonance Brain Images
Alan Wee-Chung Liew and Hong Yan
Accurate segmentation of magnetic resonance (MR) images
of the brain is of interest in the study of many brain disorders.
In this paper, we provide a review of some of the current
approaches in the tissue segmentation of MR brain images.
We broadly divided current MR brain image segmentation algorithms
into three categories: classification-based, region-based,
and contour-based, and discuss the advantages and disadvantages
of these approaches. We also briefly review our recent work
in this area. We show that by incorporating two key ideas
into the conventional fuzzy c-means clustering algorithm,
we are able to take into account the local spatial context
and compensate for the intensity nonuniformity (INU) artifact
during the clustering process. We conclude this review by
pointing to some possible future directions in this area.
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Longitudinal Functional MRI of Motor and Cognitive
Recovery Following Stroke: A Review
Erin A. Douglas, Jodi D. Edwards and Bradley
G. Goodyear
Approximately half of all strokes result in moderate-to-severe
disability, making stroke the leading cause of long-term disability
in North America. Functional magnetic resonance imaging (fMRI)
has emerged as a powerful tool to investigate functional reorganization,
temporary or permanent, during the recovery of motor and cognitive
functions following stroke, as a means to potentially predict
patient outcome and guide rehabilitation. Recently, fMRI studies
of stroke recovery have been moving towards a clinical focus,
with increased emphasis on longitudinal investigations of
recovery. In addition, the integration of fMRI with other
imaging modalities such as electroencephalography (EEG) and
near-infrared (NIR) diffuse optical tomography is becoming
increasingly important to further investigate the spatio-temporal
evolution of brain function following stroke. This article
will review the literature of longitudinal studies of motor
and cognitive recovery using fMRI, as well as discuss issues
regarding the possible implementation of fMRI for longitudinal
studies of stroke recovery in individual patients.
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From Cerebrospinal Fluid Pulsation to Noninvasive
Intracranial Compliance and Pressure Measured by MRI Flow
Studies
Noam Alperin, Monica Mazda, Terry Lichtor and Sang H. Lee
The pulsation of the cerebrospinal fluid (CSF) has fascinated
investigators of the intracranial physiology since it was
first documented by invasive CSF pressure measurements. Advances
in dynamic Magnetic Resonance Imaging (MRI) now enable visualization
of and quantitation the CSF flow dynamics and has contributed
to our understanding of the origin of CSF pulsation and its
relation to the pulsatile blood flow. This, in turn, has led
to the development of a noninvasive method for measurement
of intracranial compliance and pressure by MRI. This article
reviews the neurophysiologic and hydrodynamic principles that
are the basis of the method, it describes the implementation
of the method and validation studies to date with a non-human
primate animal model, computer simulations, healthy human
subjects and patients. The article further reviews the application
of this method to study the effect of body posture on the
cerebral physiology in humans through the relationships between
blood and CSF flow dynamics. Finally, recent results from
the application of the method in Chiari Malformations (CM)
are briefly presented as an example of a potential clinical
application of this methodology. The application to CM provided,
for the first time, evidence of the important role intracranial
compliance plays in the pathophysiology of this poorly understood
disorder. The potential diagnostic value of an MRI-based measurement
of ICP for other neurological problems is discussed.
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Gradients: The Heart of the MRI Machine
Barry L.W. Chapman
Magnetic Resonance Imaging (MRI) machines are invariably
grouped according to their main magnetic field strength. Yet
far more important to their overall performance are their
gradient coils. For it is these that determine the limitations
of the crucial parameters, TE, image speed, even the acoustic
noise produced, in every imaging sequence. To some degree,
the gradients even determine what imaging sequences are possible
of the system. For this reason it is vitally important that
every purchaser and user of MRI machines have at least some
grounding and background of gradient performance. To that
end the following paper reviews the historic development,
the current state of the art and future directions of what
is still an active ongoing research program to improve the
performance of these vital components of MRI machines.
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Clinical Applications of Cardiac Multi-Slice Computed
Tomography
Joanne D. Schuijf, Monique R.M. Jongbloed, Wouter J. Jukema,
Hildo J. Lamb , Ernst E. van der Wall, Albert de Roos and
Jeroen J. Bax
During the past few years, Multi-Slice Computed Tomography
(MSCT) has emerged as a rapidly progressing technique with
a high potential for non-invasive angiography. Recent studies
using the latest 16-slice technology have demonstrated that
the technique can detect coronary artery lesions with sensitivities
and specificities of approximately 92% and 95%, respectively.
In particular, the negative predictive value of the technique
is very high, suggesting that MSCT could play an important
role in excluding coronary artery disease prior to more invasive
procedures. Besides non-invasive coronary angiography, several
other potential applications of MSCT exist, including left
ventricular function analysis and evaluation of pulmonary
vein anatomy. Although data on these topics are still limited,
initial results appear very promising. Thus, MSCT is likely
to become a diagnostic modality integrated in clinical cardiology.
The purpose of the present review is to provide an overview
of the potential clinical applications of cardiac MSCT with
emphasis on non-invasive coronary angiography.
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Peripheral Vascular Disease: The Role of MR- Angiography
Nikolaos Economopoulos, Elias N. Brountzos and Nikolaos
L. Kelekis
Magnetic Resonance Angiography (MRA) with intravenous paramagnetic
agent has recently evolved as an accurate non invasive method,
for the imaging of the aorta and its major branches, the carotid,
the renal and pelvic arteries.
The first report of contrast enhanced MRA was published at
1993. Recently a new method was developed, employing the motion
of the MR table, during the examination (Moving bed –
bolus chase MRA) which permits the imaging of the total length
of the abdominal aorta down to the plantar arches.
In patients with critical ischemia, it is critical to visualize
the arteries beyond the trifurcation as well as the plantar
arch, in order to decide whether to perform distal bypass
or to amputate. However, transcatheter angiography commonly
cannot depict the patency of a small caliber vessel, beyond
the occlusion (runoff vessel). This vessel is called angiographically
occult vessel and its depiction is critical for the surgical
anastomosis. MRA is capable to detect very small amounts of
paramagnetic agent within the vessel lumen, thus enabling
the depiction of small caliber vessels.
Nevertheless some problems need special attention, foremost
of which is the early venous filling (venous contamination),
occuring commonly in the diabetic patient population.
The main advantages of MRA include the absence of ionizing
radiation, and the avoidance of nephrotoxic contrast media.
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Ultrasonic Elasticity Imaging as a Tool for Breast
Cancer Diagnosis and Research
Claire Pellot-Barakat, Mallika Sridhar, Karen
K. Lindfors and Michael F. Insana
Ultrasonic elasticity imaging is a promising new tool for
breast cancer diagnosis and management. Ultrasound is applied
to sense small local tissue deformations noninvasively to
image stiffness and thus exploit the large intrinsic stiffness
contrast generated during the progression of many diseases
in vivo. This paper briefly reviews several related approaches
to breast elasticity imaging to explain some of the observed
variability in breast imaging results. Preliminary clinical
results from a population of 13 patients with small and nonpalpable
breast lesions obtained with a low noise elasticity imaging
algorithm developed in our group are then reported. All the
benign lesions exhibited normal elasticity ranges. About half
of the malignant lesions were undetected with elasticity imaging
most likely because of their small size (<7mm) or softening
from the addition of fatty-replaced tissue. Other malignant
lesions were clearly identified as areas with extreme elasticity
values compared to their surroundings. We observed that some
malignant lesions did not exhibit any desmoplasic stiffening
while others showed an uncommon softening. It is clear that
by broadening the study population to include small and nonpalpable
lesions, we see much variability in elasticity image findings.
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