246 research outputs found
Diagnostic value of nuclear cardiology in coronary artery disease
This thesis investigates the diagnostic value of cardiac positron emission tomography when compared to single photon emission computed tomography for detection of coronary artery disease. This prospective study involves comparison of myocardial perfusion single photon emission computed tomography with coronary calcium scores; optimization of nuclear cardiac protocols in cardiac phantom experiments; and determination of diagnostic performance of cardiac positron emission tomography in the evaluation of myocardial viability in patients with significant coronary disease
Similarity enhancement for automatic segmentation of cardiac structures in computed tomography volumes.
International audienceThe aim of this research is proposing a 3-D similarity enhancement technique useful for improving the segmentation of cardiac structures in Multi-Slice Computerized Tomography (MSCT) volumes. The similarity enhancement is obtained by subtracting the intensity of the current voxel and the gray levels of their adjacent voxels in two volumes resulting after preprocessing. Such volumes are: a. - a volume obtained after applying a Gaussian distribution and a morphological top-hat filter to the input and b. - a smoothed volume generated by processing the input with an average filter. Then, the similarity volume is used as input to a region growing algorithm. This algorithm is applied to extract the shape of cardiac structures, such as left and right ventricles, in MSCT volumes. Qualitative and quantitative results show the good performance of the proposed approach for discrimination of cardiac cavities
What is new in pediatric cardiac imaging?
Cardiac imaging has had significant influence on the science and practice of pediatric cardiology. Especially the development and improvements made in noninasive imaging techniques, like echocardiography and cardiac magnetic resonance imaging (MRI), have been extremely important. Technical advancements in the field of medical imaging are quickly being made. This review will focus on some of the important evolutions in pediatric cardiac imaging. Techniques such as intracardiac echocardiography, 3D echocardiography, and tissue Doppler imaging are relatively new echocardiographic techniques, which further optimize the anatomical and functional aspects of congenital heart disease. Also, the current standing of cardiac MRI and cardiac computerized tomography will be discussed. Finally, the recent European efforts to organize training and accreditation in pediatric echocardiography are highlighted
Application of Dual-Energy Computed Tomography to the Evalution of Coronary Atherosclerotic Plaque
Atherosclerotic coronary artery disease is responsible for around 50 of cardiovascular deaths in USA. Early detection and characterization of coronary artery atherosclerotic plaque could help prevent cardiac events. Computed tomography (CT) is an excellent modality for imaging calcifications and has higher spatial resolution than other common non-invasive modalities (e.g MRI), making it more suitable for coronary plaque detection. However, attenuation-based classification of non-calcified plaques as fibrous or lipid is difficult with conventional CT, which relies on a single x-ray energy. Dual-energy CT (DECT) may provide additional attenuation data for the identification and discrimination of plaque components. The purpose of this research was to evaluate the feasibility of DECT imaging for coronary plaque characterization and further, to explore the limits of CT for non-invasive plaque analysis. DECT techniques were applied to plaque classification using a clinical CT system. Saline perfused coronary arteries from autopsies were scanned at 80 and 140 kVp, prior to and during injection of iodinated contrast. Plaque attenuation was measured from CT images and matched to histology. Measurements were compared to assess differences among plaque types. Although calcified and non-calcified plaques could be identified and differentiated with DECT, further characterization of non-calcified plaques was not possible. The results also demonstrated that calcified plaque and iodine could be discriminated. The limits of x-ray based non-calcified plaque discrimination were assessed using microCT, a pre-clinical x-ray based high spatial resolution modality. Phantoms and tissues of different composition were scanned using different tube voltages (i.e., different energies) and resulting attenuation values were compared. Better vessel wall visualization and increase in tissue contrast resolution was observed with decrease in x-ray energy. Feasibility of calcium quantification from contrast-enhanced scans by creating virtual n
Application of Dual-Energy Computed Tomography to the Evalution of Coronary Atherosclerotic Plaque
Atherosclerotic coronary artery disease is responsible for around 50 of cardiovascular deaths in USA. Early detection and characterization of coronary artery atherosclerotic plaque could help prevent cardiac events. Computed tomography (CT) is an excellent modality for imaging calcifications and has higher spatial resolution than other common non-invasive modalities (e.g MRI), making it more suitable for coronary plaque detection. However, attenuation-based classification of non-calcified plaques as fibrous or lipid is difficult with conventional CT, which relies on a single x-ray energy. Dual-energy CT (DECT) may provide additional attenuation data for the identification and discrimination of plaque components. The purpose of this research was to evaluate the feasibility of DECT imaging for coronary plaque characterization and further, to explore the limits of CT for non-invasive plaque analysis. DECT techniques were applied to plaque classification using a clinical CT system. Saline perfused coronary arteries from autopsies were scanned at 80 and 140 kVp, prior to and during injection of iodinated contrast. Plaque attenuation was measured from CT images and matched to histology. Measurements were compared to assess differences among plaque types. Although calcified and non-calcified plaques could be identified and differentiated with DECT, further characterization of non-calcified plaques was not possible. The results also demonstrated that calcified plaque and iodine could be discriminated. The limits of x-ray based non-calcified plaque discrimination were assessed using microCT, a pre-clinical x-ray based high spatial resolution modality. Phantoms and tissues of different composition were scanned using different tube voltages (i.e., different energies) and resulting attenuation values were compared. Better vessel wall visualization and increase in tissue contrast resolution was observed with decrease in x-ray energy. Feasibility of calcium quantification from contrast-enhanced scans by creating virtual n
Multislice computed tomography coronary angiography
__Abstract__
Computed Tomography (CT) imaging is also known as "CAT scanning"
(Computed Axia
Semi-automatic detection of the evolutionary forms of visceral leishmaniasis in microscopic blood smears
Leishmaniasis is a complex group of diseases caused by obligate unicellular and
intracellular eukaryotic protozoa of the leishmania genus. Leishmania species generate diverse
syndromes ranging from skin ulcers of spontaneous resolution to fatal visceral disease. These
syndromes belong to three categories: visceral leishmaniasis, cutaneous leishmaniasis and
mucosal leishmaniasis. The visceral leishmaniasis is based on the reticuloendothelial system
producing hepatomegaly, splenomegaly and lymphadenopathy. In the present article, a semiautomatic
segmentation strategy is proposed to obtain the segmentations of the evolutionary
shapes of visceral leishmaniasis called parasites, specifically of the type amastigote and
promastigote. For this purpose, the optical microscopy images containing said evolutionary
shapes, which are generated from a blood smear, are subjected to a process of transformation
of the color intensity space into a space of intensity in gray levels that facilitate their
subsequent preprocessing and adaptation. In the preprocessing stage, smoothing filters and
edge detectors are used to enhance the optical microscopy images. In a complementary way, a
segmentation technique that groups the pixels corresponding to each one of the parasites,
presents in the considered images, is applied. The results reveal a high correspondence between
the available manual segmentations and the semi-automatic segmentations which are useful for
the characterization of the parasites. The obtained segmentations let us to calculate areas and
perimeters associated with the parasites segmented. These results are very important in clinical
context where both the area and perimeter calculated are vital for monitoring the development
of visceral leishmaniasis
Stem cell therapy for myocardial infarction
Coronary heart disease and heart failure continue
to be significant burdens to
healthcare systems in the Western world and are predicted to become
so in emerging
economies. Despite mixed results in both experimental and clinical
studies, stem cell
therapy is a promising option for patients suffering from myocardial
infarction or
patients with chronic heart failure after myocardial infarction.
However, many issues
in the field of cellular cardiomyoplasty still need to be resolved.
This thesis describes
the experiments performed in a pre-clinical model in swine with
reperfused
myocardial infarction aiming at addressing several of these issues.
Chapter two of this thesis shows that infarct size in swine can be
measured
accurately with multislice computed tomography, as compared to the
“golden
standard” histology. This study showed that myocardial viability can
be assessed with
multislice computed tomography. Furthermore, since we used magnetic
resonance
imaging in chapter three and four, we showed that for purposes of
infarct size
assessment multislice computed tomography compares well with magnetic
resonance
imaging, which is described in chapter three. Measurement of infarct
size in patients
with acute myocardial infarction is clinically relevant because
infarct size is predictive
of left ventricular function and geometric configuration and, hence,
long-term clinical
outcome. Information on infarct size obtained with multislice
computed tomography
would enhance the diagnostic armamentarium of physicians who lack
access to
cardiac magnetic resonance imaging or encounter patients who have contra
indications to undergo magnetic resonance imaging.
The review of umbilical cord blood derived cells in the fourth
chapter of this
thesis shows a great potential of these cells to regenerate damaged
myocardium. These
cells can easily be obtained in large numbers and are not harvested
from diseased
individuals, therefore they have a great differentiation and
proliferation capacity.
Moreover, they do not raise ethical difficulties question, as do
embryonic stem cells. In
chapter five, the effect of umbilical cord blood cells is assessed
with magnetic
resonance imaging in a porcine model of myocardial infarction. There
was no positive
effect on left ventricular function or infarct size four weeks after
injection of
intracoronary administration of the umbilical cord blood cells, which
what not very
surprising since only a few of the injected cells survived.
Therefore, the immunogenic
status of these cells is not fully understood yet. However, this
study shows that
cultured umbilical cord blood cells should be used with caution when
applied
intracoronary, since their large cell size result in occluded blood
vessels, thereby
causing micro infarctions. Hence, it cannot be excluded that a
possible positive effect
of the umbilical cord blood derived cells was obscured by the
induction of micro
infarctions caused by the mode of administration. Therefore
intracoronary application
is not suitable for these cells. Although intracoronary injection is
an easy and less
invasive technique to administer cells post myocardial infarction,
intramyocardial
injection was shown to result in positive effects by Kim et al.
In contrast to the cells used in the initial experimental rodent
studies, bone marrow
derived mononuclear cells are the most common used cells in clinical
trials. In chapter
six the capacity of mononuclear cells and unselected bone marrow in a
pre-clinical
porcine model of reperfused myocardial infarction is evaluated. Our
model closely
mimics the clinical setting of myocardial infarction with regards to
the route of
administration and timing of stem cell therapy given in clinical
trials. Four weeks after
treatment with mononuclear cell injection a decrease in infarct size
is observed as
measured with magnetic resonance imaging. This was not observed after
injection of
unselected bone marrow. Histology showed that there was a trend
towards more
calcifications in the infarct area after the injection of unselected
bone marrow.
However, there was no beneficial effect of mononuclear cell or
unselected bone
marrow therapy on left ventricular function after myocardial
infarction. Our results
after mononuclear cell injection do not differ from those of the
clinical trial performed
in Leuven, Belgium by Janssens et al.
All clinical trials used the method of intermittent balloon occlusion
during
intracoronary injection of cells through the wire lumen of the
balloon catheter, based
on the assumption that this would yield increased adhesion of the
injected cells to the
vascular wall during the no-flow period, thereby leading to a higher
cell engraftment.
However, in our previous studies we used a selective probing
injection catheter
without interruption of blood flow. Therefore, we tested these
different injection
techniques in chapter seven. We observed no differences in the number
of bone
marrow mononuclear cells engrafted in the myocardium when applied
through these
two catheters (probing or balloon catheter). Therefore, the lack of
effect on left
ventricular function of bone marrow derived mononuclear cells in our
study (which
was described in chapter six), cannot be explained by the injection
technique used.
Since cultured umbilical cord blood cells can cause micro infarctions
when
administered intracoronary in healthy myocardium (chapter five), we
investigated in
chapter eight whether cultured bone marrow derived mononuclear cells
could cause
micro infarctions four days after injection in healthy myocardium. We
found that this
was the case for cultured cells, but not for freshly isolated cells.
Cultured cells are
larger in size compared to freshly isolated cells, which result in
the obstruction of the
microcirculation. Although clinical trials suggest that intracoronary
stem cell injection
is safe, cultured stem cells should be used with caution when applied
intracoronary.
The labeling of injected cells with iron to be able to track them in
vivo with
magnetic resonance imaging is assessed in chapter nine. This study
showed that due
to the hemoglobin breakdown products containing iron which is present in
hemorrhagic areas in the reperfused infarct, iron labeling of
intramyocardially
injected cells is not suitable to track the stem cells after injection.
Future directions
Future studies are required to investigate whether hemorrhage induced
signal voids
cause similar interference with cell detection with magnetic
resonance imaging after
intracoronary injection in reperfused myocardial infarctions or after
injection in non-reperfused infarcts. Gadolinium may be a more
suitable marker than iron to track cells
in vivo with magnetic resonance imaging in reperfused myocardial
infarctions.
It should be further investigated what the effect of injection of
cultured cells is,
when applying a different mode of administration, for example
intramyocardial cell
injection.
The effect of the stem cells used in our model seems to be disappointing
compared to earlier study results in small rodents. It is possible
that in our model
bone marrow derived mononuclear cells will have a positive effect on
left ventricular
function in time. Therefore, in new experiments, swine should be
monitored for a
longer follow-up time, e.g. 2, 3, 6 and 12 months. For these
experiments miniature
swine should be used.
Differentiation of bone marrow derived stem cells in vitro towards
cardiomyocytes is an option to enhance the effect of stem cell
therapy in large
mammals. However, it should always be tested whether these cultured
cells induce
microinfarctions when applied intracoronary. Pre-differentiation into
cardiomoyocytes might prevent the differentiation of injected cells
into fibroblasts or
inflammatory cells. The pre-differentiation might replace scar tissue
by viable
cardiomyocytes, and this might enhance the effect on infarct size on
left ventricular
function in vivo after injection. However, if the new cardiomyocytes
are not able to
survive in ischemic tissue, it should be investigated whether
additional cytokine
injections are needed to induce angiogenesis in the infarct tissue to
enhance cell
survival.
Patients benefit from optimal pharmacological treatment after myocardial
infarction. Over time, ejection fraction will increase and infarct
size will decrease in
patients suffering from myocardial infarction due to remodeling which
is influenced
by optimal pharmacological treatment. Therefore, in a pre-clinical
porcine model of
myocardial infarction the combination of optimal pharmacological
treatment and
stem cell therapy could be tested to evaluate the additional effect
of stem cell therapy
on the recovery of function, infarct size and the remodeling after
myocardial
infarction.
However first, in animal models, it is necessary to determine the
optimal cell
number required to obtain optimal effects of the cells on infarct
size and left
ventricular function. It should be investigated how to access the
cells (e.g. bone
marrow aspiration versus cytokine mobilization), and whether they
should be
expanded ex vivo. Second, it should be determined which cell type
will have maximal
clinical effects. Third, the optimal delivery method will have to be
determined. Finally,
understanding the mechanism of cardiac regeneration in animals will
shed a light on
the optimal therapy for patients. The potential effect of stem cell
therapy in patients
should finally be assessed in large, randomized, placebo-controlled,
double-blind
clinical trials
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