New Techniques in CT Angiography

Bolus tracking is a technique used in computed tomography imaging, to visualise vessels more clearly. A bolus of radio-opaque contrast media is injected into a patient via a peripheral intravenous cannula. Depending on the vessel being imaged, the volume of contrast is tracked using a region of interest at a certain level and then followed by the CT scanner once it reaches this level. Images are acquired at a rate as fast as the contrast moving through the blood vessels.
A maximum intensity projection (MIP) is a computer visualization method for 3D data that projects in the visualization plane the voxels with maximum intensity that fall in the way of parallel rays traced from the viewpoint to the plane of projection. This implies that two MIP renderings from opposite viewpoints are symmetrical images.
This technique is computationally fast, but the 2D results do not provide a good sense of depth of the original data. To improve the sense of 3D, animations are usually rendered of several MIP frames in which the viewpoint is slightly changed from one to the other, thus creating the illusion of rotation. This helps the viewer's perception to find the relative 3D positions of the object components. However, since the projection is orthographic the viewer cannot distinguish between left or right, front or back and even if the object is rotating clockwise or anti-clockwise.
MIP is used for the detection of lung nodules in lung cancer screening programs which utilise computed tomography scans. MIP enhances the 3D nature of these nodules, making them stand out from pulmonary bronchi and vasculature.

Where different structures have similar radiodensity, it can become impossible to separate them simply by adjusting volume rendering parameters. The solution is called segmentation, a manual or automatic procedure that can remove the unwanted structures from the image.
Some slices of a cranial CT scan are shown below. The bones are whiter than the surrounding area. (Whiter means higher attenuation.) Note the blood vessels (arrowed) showing brightly due to the injection of an iodine-based contrast agent.
Computed tomography of human brain, from base of the skull to top. Taken with intravenous contrast medium.

A volume rendering of this volume clearly shows the high density bones.

Bone reconstructed in 3D

After using a segmentation tool to remove the bone, the previously concealed vessels can now be demonstrated.

ARTIFACTS IN SPIRAL CT

Stair Step Artifacts.— Stair step artifacts appear around the edges of structures in multiplanar and three-dimensional reformatted images when wide collimations and nonoverlapping reconstruction intervals are used. They are less severe with helical scanning, which permits reconstruction of overlapping sections without the extra dose to the patient that would occur if overlapping axial scans were obtained (Fig 28). Stair step artifacts are virtually eliminated in multiplanar and three-dimensional reformatted images from thin-section data obtained with today’s multisection scanners (Fig 29).

Blood flow The liver receives blood from two sources. Oxygenated blood is supplied in the hepatic artery, a branch of the celiac trunk from the abdominal aorta. Venous blood from the entire gastrointestinal tract (containing nutrients from the intestines) is brought to the liver by the hepatic portal vein. On reaching the liver the portal vein divides into thousands of which pass in between the lobules and terminate in the sinusoids. The blood leaves the liver via a central vein in each lobule, which drains in the hepatic vein.

Summary of functions
Carbohydrate metabolism
Gluconeogenesis (the synthesis of glucose from certain amino acids, lactate or glycerol)
Glycogenolysis (the breakdown of glycogen into glucose) (muscle tissues can also do this)
Glycogenesis (the formation of glycogen from glucose)
Synthesis and secretion of bile required for emulsifying fats. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder.
Breakdown of insulin and other hormones
Protein metabolism
Lipid metabolism:
Cholesterol synthesis
The production of triglycerides (fats)
Production of blood coagulation factors I (fibrinogen), II (prothrombin), V, VII, IX, X and XI, as well as protein C, protein S and antithrombin.
Break down of hemoglobin, creating metabolites that are added to bile as pigment (bilirubin and biliverdin).
Break down of toxic substances and most medicinal products in a process called drug metabolism.
Conversion of ammonia to urea.
Storage of many substances, including glucose in the form of glycogen, vitamin B12, iron, and copper.
Red blood cell production in the first trimester fetus. By the 32nd week of gestation, the bone marrow has almost completely taken over that task.
Immunological effects – the reticuloendothelial system of the liver contains many immunologically active cells, acting as a 'sieve' for antigens carried to it via the portal system.

The arch of the aorta (Transverse Aorta) begins at the level of the upper border of the second sternocostal articulation of the right side, and runs at first upward, backward, and to the left in front of the trachea; it is then directed backward on the left side of the trachea and finally passes downward on the left side of the body of the fourth thoracic vertebra, at the lower border of which it becomes continuous with the descending aorta.
It thus forms two curvatures: one with its convexity upward, the other with its convexity forward and to the left. Its upper border is usually about 2.5 cm. below the superior border to the manubrium sterni.

The descending aorta is part of the aorta, the largest artery in the body. The descending aorta is the part of the aorta beginning at the aortic arch that runs down through the chest and abdomen. The descending aorta is divided into two portions, the thoracic and abdominal, in correspondence with the two great cavities of the trunk in which it is situated. Within the abdomen, the descending aorta branches into the two common iliac arteries which serve the legs.

The thoracic aorta is contained in the posterior mediastinal cavity.
It begins at the lower border of the fourth thoracic vertebra where it is continuous with the aortic arch, and ends in front of the lower border of the tenth thoracic vertebra, at the aortic hiatus in the diaphragm where it becomes the abdominal aorta.
At its commencement, it is situated on the left of the vertebral column; it approaches the median line as it descends; and, at its termination, lies directly in front of the column.
The vessel describes a curve which is concave forward; as the branches given off from it are small, its diminution in size is insignificant.
It has a radius of approximately 1.16 cm.[1]

Branches before thoracic aorta
The initial part of the aorta, the ascending aorta, rises out of the left ventricle, from which it is separated by the aortic valve. The two coronary arteries of the heart arise from the aortic root, just above the cusps of the aortic valve.
The aorta then arches back over the right pulmonary artery. Three vessels come out of the aortic arch, the brachiocephalic artery, the left common carotid artery, and the left subclavian artery. These vessels supply blood to the head, neck, thorax and upper limbs.

It begins at the level of the diaphragm, crossing it via the aortic hiatus at the vertebral level of T11/T12. It travels down the posterior wall of the abdomen in front of the vertebral column. It thus follows the curvature of the lumbar vertebrae, that is, convex anteriorly. The peak of this convexity is at the level of the third lumbar vertebra (L3). Some apes have a similar vertebreae structure in that they cannot masturbate is a spinal lesion occurs at L1 level. This was confirmed recently at Columbia University.
It runs parallel to the inferior vena cava, which is located just to the right of the abdominal aorta, and becomes smaller in diameter as it gives off branches.

The ascending aorta is a portion of the aorta commencing at the upper part of the base of the left ventricle, on a level with the lower border of the third costal cartilage behind the left half of the sternum; it passes obliquely upward, forward, and to the right, in the direction of the heart’s axis, as high as the upper border of the second right costal cartilage, describing a slight curve in its course, and being situated, about 6 cm behind the posterior surface of the sternum. The total length is about 5 cm in length.