CT Textbook Ch. 1 PDF

Introduction to CT Chapter 1 Part 1 Objectives: Understand the basic principles of CT Scan and Imaging Planes Ch.1 of CT text Introduction to Sectional Anatomy Ch. 1 of CS Anatomy text 1  Medical...

Introduction to CT Chapter 1 Part 1 Objectives: Understand the basic principles of CT Scan and Imaging Planes Ch.1 of CT text Introduction to Sectional Anatomy Ch. 1 of CS Anatomy text 1  Medical Image Imaging Physics Formation Instrumentati on Radiographic Patient Care Biology Anatomy 1&2 2 Introduction to CT https://www.youtube.com/watch?v=LExEbFu0VkU 3 4 Conventional Radiographs vs CT 5 Conventional Radiographs 3D object is observed as 2D image Structures are superimposed Inability to distinguish between two structures with similar densities Compton scatter due to large beam Localization of f/b requires two exposures 6 Computed Tomography Thin slices depicted in cross section Structures are not superimposed Distinguish between two tissues with similar densities Distinguish between small structures Superior Image Quality Images can be reconstructed in different planes 7  Basic Principle: Data Acquisition A finely collimated x-ray beam passes through the patient as the tube rotates 3600 X-rays continuously pass through the patient as the table moves at a pre-determined speed A detector system measures the attenuation, and the values are converted into an electrical signal Electrical signal sent to computer where information about tissues and their positional relationships are displayed as axial images 8 Process of CT Imaging Gathering x-ray absorption coefficients taken from thin sections across the body Obtaining measurements from these coefficients Reconstructing these measurement to construct an image that displays that section of the anatomy The basic process of CT consists of 4 steps 1.Data acquisition 2.Image reconstruction 3.Image display 4.Image archive 9 10 The Axial Image: Loaf of Bread Analogy Each CT slice correlates to a slice of the bread Crust of the bread: Skin White portion of the bread: Internal organs 11  CT Axial Images are often called slices CT Scout Image with Slices CT Brain Series 12 Anatomy reference line 13 Image Planes and the Gantry 14 The Axial Image Anterior RT L T Posterior 15  X & Y Axis The Z axis is not seen but it is indicated as the slice thickn RT to Left (width) is indicated by X Anterior/posterior (height) is indicated by Y Y X 16 The Matrix Display Pixels create the CT image A grid is formed from the rows and columns of pixels Each pixel contains image information Voxel includes the x, y and z axis 17 The Matrix Display Data that forms the CT slice are sectioned into elements: Width is indicated by X axis Height is indicated by Y axis X and y make up the two- Y dimensional square which is a Z pixel (picture element) Thickness: Z axis When the Z axis is considered, the result is a cube, rather than a X square which is referred to as a voxel (volume element) 18  The Axial Image All CT examinations are performed by obtaining data for a series of slices through a designated area of interest The Z axis determines the thickness of the slices (depth) Slice thickness limits the x-ray beam so that it passes only through this volume The nature of the anatomy and the Z- axis pathology suspected determines the slice thickness 1, 2, 5, 10 mm thickness available 19 Slice Thickness The smaller the object being scanned, the thinner the CT slice required Raisin bread analogy: As the loaf is sliced and examined, some slices contain raisins and others do not. If the slices are thick, it increases the possibility that even though a given slice contains a raisin, it will be obscured by the bread. If the slices are thin, the likelihood of missing a raisin decreases, but the 20 Volume Averaging Ex: A. 10-mm slice is created, and the area of pathologic tissue measures just 2 mm, normal tissue represents 8 mm and is averaged in with the pathologic tissue, potentially making the pathologic tissue less apparent on the image B. A thinner slice was taken, and the entire pathology is included in the voxel 21 Volume Data The Z axis, which is defined by Y the slice thickness, has a significant effect on the degree of Z volume averaging that is present on the image. In addition, the X and Y dimensions of the pixel also affect the likelihood of volume X averaging. The larger the X and Y dimensions (i.e., the larger the pixel), the more chance that the pixel will contain tissues of different densities. 22 The Axial Image: Loaf of Bread Analogy Each CT slice correlates to a thickness of anatomy in the Z axis 23 Interval Space between slices 5x5 5 x 10 5 x 2.5 Contiguous Gap Overlap24 Slice Thickness and Interval (Increment) Contiguous: No information is missing Overlap: Slices overlap by a predetermined amount 50% Gap: There is a gap between the margin of the last slice and the margin of the new slice. Some information is missing 25 Slice Thickness and Interval (Increment) 26 Loaf of Bread Analogy https://www.youtube.com/watch?v=lqA823kTlGY&t=4s 27  Imaging planes All directional terms are based on the body being viewed in the anatomic position. This position is used internationally and guarantees uniformity in descriptions of direction. 28 29 Review: Name the line that divides the body into anterior and posterior sections? 30 Review: Name the line that divided the body into right and left sections? 31 Review: Name the line that divided the body into upper and lower sections? 32 Oblique planes lie at an angle to one of the standard planes. 33 IMAGING PLANES Posterior and dorsal are equivalent terms used to describe movement toward the back surface of the body Anterior and ventral refer to movement forward 34 IMAGING PLANES Lateral refers to movement toward the sides of the body. Inversely, medial refers to movement toward the midline of the body. 35  IMAGING PLANES Inferior or caudal refers to movement toward the feet (down, toward the tail or feet) Superior defines movement toward the head (up) and is used interchangeably with the term cranial or cephalic. 36 IMAGING PLANES Distal and proximal are used in referring to extremities (limbs) Distal (away from) refers to movement toward the ends Proximal (close to) is defined as situated near the point of attachment 37 CT Textbook Ch. 1 38