Inverse Geometry CT

Inverse geometry CT (IGCT) is a novel concept which is being investigated as refinement of the classic third generation CT design. Although the technique has been demonstrated on a laboratory proof-of-concept device, it remains to be seen whether IGCT is feasible for a practical scanner. IGCT reverses the shapes of the detector and X-ray sources. The conventional third-generation CT geometry uses a point source of X-rays, which diverge in a fan beam to act on a linear array of detectors. In multidetector computed tomography (MDCT), this is extended in 3 dimensions to a conical beam acting on a 2D array of detectors. The IGCT concept, conversely, uses an array of highly collimated X-ray sources which act on a point detector. By using a principle similar to electron beam tomography (EBCT), the individual sources can be activated in turn by steering an electron beam onto each source target.

The rationale behind IGCT is that it avoids the disadvantages of the cone-beam geometry of third generation MDCT. As the z-axis width of the cone beam increases, the quantity of scattered radiation reaching the detector also increases, and the z-axis resolution is thereby degraded - because of the increasing z-axis distance that each ray must traverse. This reversal of roles has extremely high intrinsic resistance to scatter; and, by reducing the number of detectors required per slice, it makes the use of better performing detectors more practical. Because a separate detector can be used for each 'slice' of sources, the conical geometry can be replaced with an array of fans, permitting z-axis resolution to be preserved.

Synchrotron X-ray tomographic microscopy

Synchrotron X-ray tomographic microscopy is a 3-D scanning technique that allows non-invasive high definition scans of objects with details as fine as 1,000th of a millimetre, meaning it has two to three thousand times the resolution of a traditional medical CT scan.
Synchrotron X-ray tomographic microscopy has been applied in the field of palaeontology to perform non-destructive internal examination of fossils, including fossil embryos to be made. Scientists feel this technology has the potential to revolutionize the field of paleontology.
Archaeologists are increasingly turning to Synchrotron X-ray tomographic microscopy as a non-destructive means to examine ancient specimens.

Chest CT Scan

CT is excellent for detecting both acute and chronic changes in the lung parenchyma. (parenchyma means internals, in this case, of the lungs. It is relevant here because normal two dimensional x-rays do not show up defects in the internals of the lungs). A variety of different techniques are used depending on the suspected abnormality. For evaluation of chronic interstitial processes (emphysema, fibrosis, and so forth), thin sections with high spatial frequency reconstructions are used - often scans are performed both in inspiration and expiration. This special technique is called High resolution CT (HRCT). HRCT is normally done with thin section with skipped areas between the thin sections. Therefore it produces a sampling of the lung and not continuous images. Continuous images are provided in a standard CT of the chest.

Pulmonary Angiogram

CT pulmonary angiogram (CTPA) is a medical diagnostic test used to diagnose pulmonary embolism (PE). It employs computed tomography to obtain an image of the pulmonary arteries.
It is a preferred choice of imaging in the diagnosis of PE due to its minimally invasive nature for the patient, whose only requirement for the scan is a cannula . Before this test is requested, it is usual for the referring clinician to have carried out a D-dimer blood test and requested a chest X-Ray to rule out any other possible differential diagnosis.
MDCT (multi detector CT) scanners give the optimum resolution and image quality for this test. Images are usually taken on a 0.625mm slice thickness, although 2mm is sufficient. 50 - 100 mls of contrast is given to the patient at a rate of 4 ml/s. The tracker/locator is placed at the level of the Pulmonary Arteries, which sit roughly at the level of the carina. Images are acquired with the maximum intensity of radio-opaque contrast in the Pulmonary Arteries. This is done using bolus tracking.

CT Pulmonary Angiogram

CT pulmonary angiogram (CTPA) is a medical diagnostic test that employs computed tomography to obtain an image of the pulmonary arteries. Its main use is to diagnose pulmonary embolism.

On CTPA, the pulmonary vessels are filled with contrast, and appear white. Any mass filling defects (embolus or other matter such as fat or amniotic fluid) appears darker. Generally, the scan should be complete before the contrast reaches the left side of the heart and the aorta, which could result in artifacts.

Pulmonary Embolism

Pulmonary embolism (PE) is a blockage of the pulmonary artery usually when a venous thrombus , becomes dislodged from its site of formation and embolizes to the arterial blood supply of one of the lungs. This process is termed thromboembolism.
Symptoms may include difficulty breathing, pain in the chest during breathing, and in more severe cases collapse, circulatory instability and sudden death. Treatment, usually, is with anticoagulant medication, such as heparin and warfarin, and rarely with thrombolysis or surgery. In other, rarer forms of pulmonary embolism, material other than a blood clot is responsible; this may include fat or bone , air, clumped tumor cells, and amniotic fluid (affecting mothers during childbirth).

Pulmonary artery

The pulmonary arteries carry blood from the heart to the lungs. They are the only arteries (other than umbilical arteries in the fetus) that carry deoxygenated blood.
In the human heart, the pulmonary trunk (pulmonary artery or main pulmonary artery) begins at the base of the right ventricle. It is short and wide - approximately 5 cm (2 inches) in length and 3 cm (1.2 inches) in diameter. It then branches into two pulmonary arteries (left and right), which deliver deoxygenated blood to the corresponding lung.

Pulmonary hypertension occurs alone and as a consequence of a number of lung diseases. It can be a consequence of heart disease (Eisenmenger's syndrome) but equally a cause (right-ventricular heart failure); it also occurs as a consequence of pulmonary embolism and scleroderma. It is characterised by reduced exercise tolerance. Severe forms, generally, have a dismal prognosis.