PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 11556801

Modified weighting method for forward-looking ring-annular arrays.

J R Crowe·J D Hamilton·D N Stephens·Y Wang·M O'Donnell
View original source ↗Export metadata ↓

Abstract

Side-looking Intravascular Ultrasound Systems (IVUS) systems provide high resolution cross-sectional images of vascular structure. However, blood velocity estimation is hampered by the orthogonality of the primary blood flow direction to the imaging plane, and do not image in front of the catheter. A forward-looking aperture would improve the ability to guide interventions and allow Doppler processing for improved blood speed estimates; however, catheter-based systems delivered over a guide wire limit forward-looking array geometry to annular variations. Unfortunately, the imaging characteristics of annular arrays are inferior to a full aperture disk. A modified weighting method for a practical synthetic phased, ring-annular array is presented that achieves a transmit-receive aperture and on-axis performance comparable to a full aperture disk array.

Explore related subjects

Blood Flow VelocityCoronary VesselsHumansUltrasonography, InterventionalJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

J R Crowe, J D Hamilton, D N Stephens, Y Wang, M O'Donnell. 2001. Modified weighting method for forward-looking ring-annular arrays.. https://doi.org/10.1177/016173460102300102

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2003

Pharmacological rationale for the use of somatostatin and analogues in portal hypertension.

Somatostatin and its analogue octreotide have been used for two decades to treat oesophageal variceal haemorrhage. The drug was introduced because of its capacity to decrease portal venous pressure without major side effects. In clinical trials assessing the efficacy of somatostatin and long-acting analogues in arresting variceal haemorrhage, conflicting results have been obtained. Furthermore, in haemodynamic studies evaluating the effects of somatostatin and analogues in patients with cirrhosis, divergent effects were observed. The main reason for these differences is probably related to different affinities of the drugs for different somatostatin receptor subtypes. The effects of somatostatin and analogues are mediated via five different G-protein coupled receptors (somatostatin receptor subtypes 1-5), which regulate the activity of ion channels (Ca2+, K+, Na+ and Cl-) and enzymes (adenyl cyclase, phospholipase C, phospholipase A2, phosphoinositide 3-kinase and guanylate cyclase) responsible for the synthesis or degradation of intracellular second messengers including cyclic AMP, inositol 1,4,5-trisphosphate, diacylglycerol and cyclic GMP. Despite universal use of somatostatin, the cellular and biochemical mechanisms of its effects in portal hypertension are relatively poorly studied and remain incompletely understood. In this review, we summarize relevant signal transduction of somatostatin and analogues, the haemodynamic effects of the drugs and the possible mechanisms by which these effects are mediated.

Blood Flow Velocity↗
PubMed2003

Estimation of capillary density in human skeletal muscle based on maximal oxygen consumption rates.

A previously developed Krogh-type theoretical model was used to estimate capillary density in human skeletal muscle based on published measurements of oxygen consumption, arterial partial pressure of oxygen, and blood flow during maximal exercise. The model assumes that oxygen consumption in maximal exercise is limited by the ability of capillaries to deliver oxygen to tissue and is therefore strongly dependent on capillary density, defined as the number of capillaries per unit cross-sectional area of muscle. Based on an analysis of oxygen transport processes occurring at the microvascular level, the model allows estimation of the minimum number of straight, evenly spaced capillaries required to achieve a given oxygen consumption rate. Estimated capillary density values were determined from measurements of maximal oxygen consumption during knee extensor exercise and during whole body cycling, and they range from 459 to 1,468 capillaries/mm2. Measured capillary densities, obtained with either histochemical staining techniques or electron microscopy on quadriceps muscle biopsies from healthy subjects, are generally lower, ranging from 123 to 515 capillaries/mm2. This discrepancy is partly accounted for by the fact that capillary density decreases with muscle contraction and muscle biopsy samples typically are strongly contracted. The results imply that estimates of maximal oxygen transport rates based on capillary density values obtained from biopsy samples do not fully reflect the oxygen transport capacity of the capillaries in skeletal muscle.

Blood Flow Velocity↗