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Thứ Hai, 28 tháng 4, 2014
Thứ Sáu, 25 tháng 4, 2014
ARFI for KIDNEYS: AFFECTIONS of TISSUE FIBROSIS or RENAL BLOOD FLOW
ABSTRACT:
Objectives—The aim of this study was to identify the main
influencing factor of the shear wave velocity (SWV) of the kidneys measured by
acoustic radiation force impulse elastography.
Methods—The SWV was measured in the kidneys of 14 healthy
volunteers and 319 patients with chronic kidney disease. The estimated
glomerular filtration rate was calculated by the serum creatinine concentration
and age. As an indicator of arteriosclerosis of large vessels, the brachial-ankle pulse wave velocity was
measured in 183 patients.
Results—Compared to the degree of interobserver and
intraobserver deviation, a large variance of SWV values was observed in the
kidneys of the patients with chronic kidney disease. Shear wave velocity values
in the right and left kidneys of each patient correlated well, with high
correlation coefficients (r = 0.580–0.732). The SWV decreased concurrently with a decline in the estimated glomerular
filtration rate. A low SWV was obtained in patients with a high brachial-ankle pulse
wave velocity. Despite progression of renal fibrosis in the advanced stages of
chronic kidney disease, these results were in contrast to findings for chronic
liver disease, in which progression of hepatic fibrosis results in an increase
in the SWV. Considering that a high brachial-ankle pulse wave velocity
represents the progression of arteriosclerosis in the large vessels, the
reduction of elasticity succeeding diminution of blood flow was suspected to be
the main influencing factor of the SWV in the kidneys.
Conclusions—This study indicates that diminution of blood
flow may affect SWV values in the kidneys more than the progression of tissue
fibrosis. Future studies for reducing data variance are needed for effective
use of acoustic radiation force impulse elastography in patients with chronic kidney disease.
Key Words—acoustic radiation force impulse; brachial-ankle
pulse wave velocity; chronic kidney disease; genitourinary ultrasound; renal
blood flow; shear wave velocity.
Quantification of Kidney Stiffness by ARFI Elastography
The SWV was measured with an Acuson S2000 ultrasound system
(Siemens Medical Solutions) using a 3.5-MHz convex probe. Kidney images were
obtained in the prone position so that the longitudinal section was visible on the
monitor. An ROI of 10 × 5 mm was set adjacent to the inferior pole of the
cortex in the dorsal area of the renal parenchyma to exclude vessels depicted
by the color Doppler mode. Placement of the ROI was accurate in almost all
participants. To prevent respiratory motion the SWV was measured on inhalation
breath holding 5 to 6 times consecutively by a sonographer. The mean SWV values
were calcul ated in the right and left kidneys, respectively. While being
blinded to the clinical data, 2 experienced sonographers (J.T. and Y.T.) performed ARF elastography.
Discussion
In ARFI elastography for chronic liver disease, the SWV increases
in more advanced stages because progressing interstitial fibrosis predominantly
affects tissue elasticity, as observed in liver cirrhosis.
However, the main affecting factor of ARFI elastography in
the kidneys has not been elucidated presumably for two reasons. Namely, a large variance of SWV values in the kidneys, as demonstrated by Goertz
et al, has yielded results with low reliability, and the degree of interstitial
fibrosis in the kidneys of patients with chronic kidney disease is not as
marked as that in chronic liver disease. Since approximately 20% of cardiac output
flows into the kidneys, which constitute less than 1% of body mass, we
suspected that renal blood flow might be the main influencing factor of the SWV
in the kidneys instead of interstitial fibrosis.
In the feasibility study, interobserver and intraobserver
deviation was proven to be small when the SWV was measured in the kidney of a
healthy volunteer. Although no significant correlation was obtained between SWV
and estimated GFR values in 14 healthy volunteers in the first trial, a
significant correlation was found between the SWV and estimated GFR when the ROI setting and measurement timing
during arterial pulsation were reviewed. Interestingly, the SWV decreased
concurrently with a decline in the estimated GFR in all cohorts of patients
with chronic kidney disease despite the large variance noted. This finding
means that kidney tissue stiffness decreases at advanced stages of chronic
kidney disease despite the increasing prominence of interstitial fibrosis. Low
SWV values were obtained in patients with a high brachial-ankle PWV.
Considering that the brachial-ankle PWV represents arteriosclerosis of large vessels,
we hypothesized that diminution of renal blood flow succeeding atherosclerosis
of renal arteries may cause decreased elasticity of renal parenchyma in
advanced chronic kidney disease. We also assumed that the large variance of SWV
values in the kidneys of patients with chronic kidney disease derived from the
structural heterogeneity of renal parenchyma and pressure fluctuation resulting from pulsating blood flow, rather than technical variance in measurement.
Renal parenchyma is grossly divided into the cortex and
medulla. The cortex consists of proximal and distal tubules and renal
glomeruli. The medulla mostly consists of the loop of Henle and the lower part
of the collecting tubule. To meet the large oxygen consumption for massive reabsorption, the renal tubules are surrounded by a dense vascular
plexus in both the cortex and medulla. In kidneys with low estimated GFRs, the number of
glomeruli with global sclerotic changes increases. The renal tubule, located
downstream of the sclerosing glomerulus, becomes atrophic, and peritubular
fibrosis subsequently progresses.
Blood flow in the peritubular vascular plexus decreases according
to sclerotic changes of the glomeruli, since blood flows from the glomeruli to
the vascular plexus. Considering the remarkable damage of microcirculation in
advanced chronic kidney disease, it is conceivable that blood flow rather than
interstitial fibrosis dominantly affects the elasticity of kidney tissue in
chronic kidney disease. In addition, it is widely known that the incidence of
cardiovascular events increases concurrently with a decline in the estimated GFR. As shown in Figure 6,
patients with chronic kidney disease who had a high brachial-ankle PWV tended
to have a low SWV in the kidney. From these results, we strongly suspected that
a combination of microcirculatory damage in the renal tissue and
arteriosclerosis of renal arteries diminished renal blood flow and reduced kidney
stiffness in patients with chronic kidney disease.
This study had several limitations. Since our hypothesis was
based on hemodynamic changes in the kidneys, parameters directly related to
renal blood flow and renal vessel resistance should be demonstrated. We
measured the peak systolic velocity (Vmax) and end-diastolic velocity (Vmin) by
using Doppler sonography and calculated the resistive index by the following equation: resistive index =(Vmax– Vmin)/Vmax. However, the data fit between the estimated
GFR and Vmax and the estimated GFR and resistive index was poor (data not
shown). For the ARFI measurement, ROI setting was frequently difficult when
measuring the SWV in the kidneys of patients with advanced chronic kidney
disease. In patients with high estimated GFRs, the SWV could be measured at the cortex because the
thickness of the renal parenchyma was still sufficient.
However, for patients with advanced chronic kidney disease,
the renal parenchyma was atrophic, and distinction between the cortex and
medulla was often difficult.
Renal atrophy prevented accurate SWV measurement in 4 patients
and Vmax and Vmin measurement in 16 patients. Several potential future studies
are proposed. Instead of the brachial-ankle PWV, the cardio-ankle vascular
index could be used as a novel indicator of arterial stiffness. Since the
cardio-ankle vascular index is less affected by systemic blood pressure, it can
be used as an alternative method to evaluate large-vessel arteriosclerosis.
Shear wave velocity values can be normalized by systemic blood pressure and synchronization
with electrocardiography, which ensures consistent aortic pressure during the
cardiac cycle. Early-stage SWV assessment of the kidneys in diabetic patients
may be feasible because of the hyperdynamic blood flow of the diabetic kidney in the early stages. If
our hypothesis is correct, SWV values should be high in those kidneys. A
comparison of ARFI assessment with surrogate markers of tissue fibrosis could
be performed.
In conclusion, our study suggests that the SWV measured by
ARFI elastography in patients with chronic kidney disease may represent the
diminution of blood flow that succeeds arteriosclerosis, as opposed to the
development of renal fibrosis. In our results, the standard deviations of SWV
values were considerably high. However, further improvement of this method may result in obtainment of more
consistent SWV values in the kidneys.
Thứ Năm, 24 tháng 4, 2014
ULTRASOUND IMPROVING SENSORY DISCRIMINATION
New research has demonstrated that ultrasound can be
employed to modulate brain activity to heighten sensory perception in humans, similar
to how bats use ultrasound to help guide them at night.
Virginia Tech Carilion Research Institute (Roanoke, VA, USA;
http://research.vtc.vt.edu) scientists
have demonstrated that ultrasound directed to a specific region of the brain
can improve performance in sensory discrimination. The study’s findings,
published online January 12, 2014, in the journal Nature Neuroscience, provides
the first validation that low-intensity, transcranial focused ultrasound can
modulate human brain activity to raise perception.
“Ultrasound has great potential for bringing unprecedented
resolution to the growing trend of mapping the human brain’s connectivity,”
said Dr. William Tyler, an assistant professor at the Virginia Tech Carilion
Research Institute, who led the study. “So we decided to look at the effects of
ultrasound on the region of the brain responsible for processing tactile sensory inputs.”
The scientists delivered focused ultrasound to an area of
the cerebral cortex that processes sensory information received from the hand.
To stimulate the median nerve, they positioned a small electrode on the wrist
of human volunteers and recorded their brain responses using electroencephalography
(EEG). Then, right before stimulating the nerve, they began delivering
ultrasound to the targeted brain region.
The investigators discovered that the ultrasound both
decreased the EEG signal and weakened the brain waves responsible for encoding tactile stimulation. The scientists then administered two
classic neurologic tests: the two-point discrimination test, which gauges an
individual’s ability to distinguish whether two close by objects touching the skin are truly two distinct points, instead of
one; and the frequency discrimination task, a test that measures sensitivity to
the frequency of a chain of air puffs.
What the scientists found was unanticipated. The study
participants receiving ultrasound showed substantial improvements in their capability
to differentiate pins at closer distances and to single out small frequency
differences between successive air puffs. “Our observations surprised us,” said
Dr. Tyler. “Even though the brain waves associated with the tactile stimulation
had weakened, people actually got better at detecting differences in
sensations.”
The researchers wanted to know why would brain response
suppression to sensory stimulation heighten perception, and Dr. Tyler theorized
that the ultrasound affected an important neurologic balance. “It seems paradoxical, but we suspect that the
particular ultrasound waveform we used in the study alters the balance of
synaptic inhibition and excitation between neighboring neurons within the cerebral cortex,” Dr. Tyler said. “We believe
focused ultrasound changed the balance of ongoing excitation and inhibition
processing sensory stimuli in the brain region targeted and that this shift prevented the spatial spread of excitation in
response to stimuli resulting in a functional improvement in perception.”
To determine how well they could isolate the effect, the
researchers moved the acoustic beam 1 cm in either direction of the original
site of brain stimulation, and the effect disappeared. “That means we can use ultrasound to target an area of the brain as small
as the size of an M&M [a popular US candy about 1 cm in diameter,]” Dr.
Tyler said. “This finding represents a new way of noninvasively modulating human brain activity with a better spatial resolution
than anything currently available.”
The scientists, based on the findings of the current study
and an earlier one, concluded that ultrasound has a greater spatial resolution
than two other leading noninvasive brain stimulation technologies –
transcranial magnetic stimulation, which uses magnets to activate the brain,
and transcranial direct current stimulation, which uses slight electrical
currents delivered directly to the brain through electrodes positioned on the
head.
“The work by Jamie Tyler and his colleagues is at the
forefront of the coming tsunami of developing new, safe, yet effective
noninvasive ways to modulate the flow of information in cellular circuits
within the living human brain,” said Dr. Michael Friedlander, executive
director of the Virginia Tech Carilion Research Institute and a neuroscientist
who specializes in brain plasticity.
“This approach is providing the technology and proof of
principle for precise activation of neural circuits for a range of important
uses, including potential treatments for neurodegenerative disorders,
psychiatric diseases, and behavioral disorders. Moreover, it arms the
neuroscientific community with a powerful new tool to explore the function of the healthy human brain, helping us understand
cognition, decision-making, and thought. This is just the type of breakthrough called for in President Obama’s BRAIN [Brain Research
through advancing Innovative Neurotechnologies, also referred to as the Brain
Activity Map Project] Initiative to enable dramatic new approaches for
exploring the functional circuitry of the living human brain and for treating Alzheimer’s
disease and other disorders.”
Image: William Tyler, an assistant professor at the Virginia
Tech Carilion Research Institute, studied the effects of ultrasound on the
region of the brain responsible for processing tactile sensory inputs (Photo
courtesy of Jim Stroup / Virginia Tech)
Thứ Tư, 23 tháng 4, 2014
Carotid Narrowing
Carotid narrowing tied to memory, thinking decline
By AuntMinnie.com staff writers
April 22, 2014 -- The narrowing of the carotid artery may be linked to problems in learning, memory, thinking, and decision-making, according to research to be presented at this week's American Academy of Neurology annual meeting in Philadelphia.
A team of researchers led by Dr. Brajesh Lal of the University of Maryland found a higher risk of symptoms in patients with narrowing of the carotid artery than in patients with similar risk factors but no carotid artery narrowing.
The team studied 67 people with asymptomatic carotid stenosis (ACS) and a 50% reduction in the diameter of the artery, as well as 60 people with vascular risk factors but without ACS. The risk factors included diabetes, high blood pressure, high blood cholesterol, and coronary artery disease, according to the team.
All study participants received extensive testing for overall thinking abilities and specific aspects of thinking, such as processing speed, learning, memory, decision-making, and language. The group of patients with ACS performed significantly worse on the overall memory and thinking tests, including tests for motor and processing speed, as well as learning and memory, according to the researchers. They did not find a difference in language scores between the two groups.
If these findings are confirmed in larger studies, they hold significant implications for new treatment targets and open the door for more questions, such as whether these patients should be treated more aggressively with medications, cognitive rehabilitation, or even surgery to open up the artery, Lal said in a statement. He anticipates a large number of follow-up studies to search for causes and the best treatment option for this newly identified morbidity associated with carotid narrowing, he added.
Thứ Ba, 22 tháng 4, 2014
MEDULLARY THYROID CARCINOMA (MTC) with REMARKABLE CALCIFICATIONS
Various patterns of calcifications may be seen in thyroid cancers on ultrasonography (USG)
of thyroid. Coarse calcifications seen in medullary thyroid carcinoma
(MTC) are generally associated with posterior shadowing on thyroid ultrasound.
We briefly report
this case of MTC with an emphasis on its
radiological features.
A 45-year-old post-menopausal female presented with a goiter
(8 cm ×
7 cm) of ten
years duration. History was uneventful otherwise. Thyroid function tests were:
free T3-2.20 pg/ml (ref. range: 1.71-
3.71), free T4-1.18 ng/100ml (ref.
range: 0.7-1.48) and TSH-1.42 µIU/ml (ref. range: 0.35-4.94) respectively. Subsequently, thyroid
ultrasound revealed prominent
calcifications and increasedvascularity (Figure
1), (Figure 2).
Computed Tomography (CT) scan of neck showed large (80 mm × 78 mm) well defined,
calcified mass lesion in the left lobe of the thyroid (Figure 3). Fine
needle aspiration biopsy (FNAB) confirmed
evidence of MTC. A highly elevated calcitonin (20,000 pg/ml) (ref. range: < 5 pg/ml) was
consistent with the diagnosis of MTC.
MTC may be associated
with dense, irregular foci of calcifications
which are in contrast with homogeneous calcifications of other
thyroid tumors. MTC,
first described by Hazard et al. in 1959, has become the focus of
increasing clinical and experimental investigations.
However, in thyroid
carcinomas, ultrasonographic evidence of
an abundance of calcifications may
be rarely seen nowadays due to improved
health awareness and earlier diagnosis. To conclude, in an asymptomatic patient
with long standing goiter, coarse
macrocalcifications in imaging findings should make the physician vigilant in ruling
out MTC.
Thứ Hai, 14 tháng 4, 2014
Anal and Rectal Endosonography in Clinical Practice
Anal (EcoA) and rectal endosonography (EcoEAR) is a useful test in the evaluation of patients with anorectal pathology. However, there is no clear consensus on its indications.
The aim of this study was to determine the opinion of clinicians regarding the current indications and usefulness of this diagnostic test in daily clinical practice.
A cross-sectional observational study was conducted using a survey sent to the services of General surgery in a specific area of Spain.
The clinical usefulness of the test was evaluated using an analog scale from 0 (lowest value) to 10 (maximum utility) for each pathology. Of the 47 hospitals, 23 responded to the questionnaire (48.9%). The average number of ultrasounds performed in these centers was 217 per year (standard deviation: 140.1, range 73–450) during the last 3 years.
The most common indications for this test were: rectal tumor (85%), anal fistula (80%), and fecal incontinence (70%). This test was suggested more, depending on availability in the hospital itself. In conclusion, anal and rectal endosonography remains a very useful diagnostic clinical test in the opinion of clinicians in general and digestive surgery, especially in the evaluation of patients with anal fistula, fecal incontinence, or rectal tumors.
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