[Imaging Blood Flow and Pulsation of Retinal Vessels with Full-Field Swept-Source OCT]. / Darstellung von Blutfluss und Pulsation in retinalen Gefäßen mit Full-Field-Swept-Source-OCT.

Optical coherence tomography (OCT) uses interference to image the retina with high axial resolution. In the last 25 years, new technologies have permitted a steady increase in imaging speed, which made it possible to enlarge the imaged field and to avoid motion artefacts. The speed and precision of retinal imaging is now limited by photodamage of the retina caused by the focused OCT beam and by the speed of the scanning mechanics. Full-field swept-source (FF-SS)-OCT decreases irradiance on the retina and dispenses moving parts by using a camera to acquire the full volume of the retina in parallel. Here we show that FF-SS-OCT is rapid and precise enough to image pulsation in the retina induced by the heart beat. Series of OCT volumes 1.8 × 0.7 mm wide and 1.8 mm deep were recorded in young volunteers over a few cycles of the heart beat. Morphology of the retinal vessels, blood flow and tissue motion as caused by vessel pulsation were calculated from the OCT data. FF-SS-OCT was able to visualise the main structures of the neuronal retina, including vessels and small capillaries and without any motion artefacts. Information on three different dynamic processes was obtained from only one recorded series of OCT volumes: pulsation of blood flow and blood pressure in retinal vessels as well as pulsation of the choroid. Delays between arterial and venous pulse and delay between pulsation in retinal and choroidal vessels were calculated. With a time resolution of 0.5 ms, FF-SS-OCT is able to visualise previously unmeasurably fast changes in the retina, including the propagation of pulse waves.

Magnetic resonance imaging of the ligamentous structures of the occipitoatlantoaxial region in the dog.

Our objectives were to establish a magnetic resonance (MR) protocol for the examination of, and then describe, the normal ligaments and the supporting structures of the occipitoatlantoaxial region. This was done in 10 cadaver dogs. In addition, MR images of three patients with cervical pain localized to the occipitoatlantoaxial region are included to provide examples of ligamentous abnormalities. All ligaments were hypointense in all pulse sequences. The apical, dorsal atlantoaxial, and dorsal longitudinal vertebral ligaments were seen best in the sagittal T1W and PD-weighted images. The transverse ligament was best visualized in the transverse plane in all pulse sequences and appeared to be confluent with the dorsal longitudinal vertebral ligament dorsal to the dens in the sagittal plane. A 20° dorsal plane reconstructed image in 0.6-mm slice thickness was necessary to visualize the alar ligaments, which were visible in 9/10 dogs. The dorsal longitudinal vertebral ligament appeared continuous with the apical ligament and tectorial membrane. Abnormalities in clinically affected dogs included thickening of the alar ligaments, absence of transverse ligament and elongation, and irregularity of the apical ligament.

Observations on the muscles of the eye of the bowhead whale, Balaena mysticetus.

The muscles of the eyelids and the extraocular muscles of mysticete whales are poorly described for a variety of reasons, including considerable difficulty in obtaining specimens. Our objective is to provide such a description for the bowhead whale, Balaena mysticetus. This study has examined the gross anatomy of the region in six specimens (five adults, one fetus) of the bowhead whale. Results show that the muscles associated with the eye are well developed and possess several distinctive features. For example, precise limits of each extraocular muscle are difficult to determine along their entire length because these muscles intermingle with one another near their insertion. Furthermore, some fibers from these muscles (except the retractor bulbi) also insert into the eyelids. Pulling on these muscles to simulate contraction results in movement of the eyelids and suggests a role for these muscles in palpebral retraction. Insertion of a large levator palpebrae superioris muscle into the upper eyelid further enhances opening of the palpebral fissure. Another unusual feature is the presence of tunnel-like structures that redirect the dorsal and ventral oblique muscles. The dorsal oblique muscle is redirected caudally about 90 degrees, then directed medially by another 90 degrees. These directional changes are accomplished via a connective tissue tunnel derived in part from the fibrous connective tissue of the dorsal rectus and the levator palpebrae superioris muscles. In most terrestrial mammals, a similar change in direction is accomplished by a cartilaginous trochlea. The ventral oblique muscle originates via a slender tendon from the frontal bone and undergoes a similar radical change in direction. Its tendon of insertion undergoes about a 90-degree change in direction that is accomplished through a tunnel-like structure derived from fibrous connective tissue of the ventral rectus muscle. Based on the morphology of the musculature presented, it is likely that the eyeballs and eyelids of the bowhead whale are quite mobile and appear capable of complex movement. The possibility of retraction and protrusion of the eyeball is discussed.

Observations on the external morphology and vasculature of a fetal heart of the bowhead whale, Balaena mysticetus.

BACKGROUND: Specialized demands within the aquatic environment for over some 60 million years have shaped unique morphological expressions in the whales, dolphins, and porpoises (Cetacea). Detailed consideration of these features, particularly in the great whales, has often been constrained by difficulties in securing adequate specimens for study. We had the opportunity to examine external heart morphology in a rarely obtained and prepared specimen from the bowhead whale, Balaena mysticetus. METHODS: The external morphology and in situ relations of a formalin-perfused heart were examined grossly in a near-term bowhead fetus. Latex injections assisted visualization of coronary vasculature. Magnetic resonance imaging was used to clarify heart positioning within the thoracic cavity in two younger (early and mid-gestational) intact fetuses. RESULTS: The heart was globular in form, with a blunt apex and wide base; it was laterally broad relative to height yet considerably compressed between nearly planar atrial (diaphragmatic) and auricular (sternocostal) surfaces. The heart constituted 0.01 of body mass in the near-term fetus. Within the thoracic cavity, the heart tilted forward on its long axis, placing the great basal vessels in the region of the thoracic inlet. The aorta extended forward from mid-base in parallel with the pulmonary trunk, arched sharply to the left, producing in succession the brachiocephalic trunk, left common carotid artery, and the left subclavian artery. Bifurcation of the brachiocephalic trunk yielded the right common carotid and right subclavian arteries. The distal portion of the aortic arch was linked to the pulmonary trunk via the ductus arteriosus. The aorta then swung caudally over the heart base, descending beneath the bodies of the thoracic vertebrae. The ascending aorta featured three bulbous sinuses immediately distal to the three semilunar cusps of the aortic valve. Originating along the distal boundaries of the left and right sinuses were the left and right coronary arteries. The arteries were similar in size and, because each sent contributions along their respective coronary and interventricular grooves, the heart can be described as bilateral relative to arterial supply. Anastomoses were common within and between the two arteries. Venous return from the heart was comprised of the great, middle, and right cardiac veins, all three converging in the coronary sinus. The right cardiac vein also included tributaries that emptied directly into the right atrium. CONCLUSIONS: External heart morphology in the fetal bowhead whale examined was distinguished by a laterally broad conformation with significant compression between its cranial and caudal surfaces. Aortic bulb configuration in combination with an expandable aortic arch may support blood service to the heart during diastole. Vascular service to the heart featured a complex vessel network with extensive intraarterial and intravenous anastomoses that enable many alternate blood perfusion pathways and may be adaptive to water-column-pressure fluctuations experienced by a large diving mammal.

Disruption of the caudal component of the reciprocal apparatus in two horses.

Two horses became acutely lame following a fall during strenuous exercise and were diagnosed as having disruption of the caudal component of the reciprocal apparatus. Clinical signs consisted of lameness of the right pelvic limb, characterized by flexion of the hock and simultaneous extension of the stifle. Radiography revealed an avulsion fracture from the supracondylar tuberosity and fossa of the distal portion of the femur in one horse. Clinical and radiographic findings indicated avulsion of the lateral origin of the gastrocnemius and superficial digital flexor muscles. Treatment consisted of stall rest, limb immobilization, and phenylbutazone administration. One horse recovered to soundness and the other deteriorated and was euthanatized.