ct chest basis

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Ct chest : 

Ct chest What the mind does not know, the eye cannot see

CT CHEST : 

CT CHEST BASIS

Ct chest : 

Ct chest Two dimensional representation of three dimensional slice Internal structure of an object can be reconstructed from multiple projections Image is composed of multiple picture elements known as pixels Pixel represents attenuation of unit volume of tissue known as voxel

Slide 4: 

Godfrey Housnefield-1st to introduce CT in 1972 Consists of x ray sourse,collimators,x ray detectors , associated electronics.

CONVENTIONAL CT : 

CONVENTIONAL CT Series of individual cross sectional slices obtained during suspended respiration After each slice is obtained patient is allowed to breath while table is moved to next position Affected by variation in depth of respiration This method of obtaining a series of slices is known as incremental scanning

Spiral Ct : 

Spiral Ct Helical or volumetric ct Allows continuous scanning X ray beam travel spiral curve in relation to patient Spiral of information is acquired in single breath hold Unaffected by variation in depth of respiration Better in detection of pulmonary nodule,Av malformation, central airway abnormality

Spiral ct : 

Spiral ct

spiral ct : 

spiral ct

Advantages of spiral ct : 

Advantages of spiral ct High quality multiplanar, three dimensional image display Basis of virtual bronchoscope Allows major portions or entire chest to be scanned during a single breath hold Eliminates motion artefacts

Ct .technical parameters : 

Ct .technical parameters Slice thickness Slice spacing Field of view Reconstruction algorithm Image display settings

Slice thickness : 

Slice thickness Single attenuation value of voxel represents average of all attenuation of all various structures within it Thicker the slice greater the averaging called partial volume effect Partial volume effect reduced by thinner section Determined by size of structure being assessed and number of scans required to evaluate the patient

Hrct versus convention ct : 

Hrct versus convention ct

Slice spacing : 

Slice spacing Adequate assessment of patient 10 mm interval 1 to 2 mm slice with 10 mm interval allows only 10 to 20% of lung Improved spatial resolution allows better assessment of normal and abnormal findings Pulmonary metastasis requires spiral ct with 5 to 7mm thick sections Trachea and central bronchi 3 to 5mm thick spiral ct Pulmonary parenchyma and peripheral bronchi requires 1 to 2 mm sections

Reconstruction algorithm : 

Reconstruction algorithm Lung parenchyma :high spatial algorithm High spatial algorithm reduces smoothing Better depiction of normal and abnormal parenchymal interface Mediastinum and chest wall standard soft tissue algorithm

Reconstruction algorithm on image quality : 

Reconstruction algorithm on image quality

Reconstruction algorithm : 

Reconstruction algorithm

Image display settings : 

Image display settings Two parameters: window width and window level Average density of each voxel : Hounsfield unit These units are arbitrary so 0 is for water,- 1000 for air Range of Hounsfield in thorax is wider ranging from -850HU for aerated lung to 700HU for ribs Display of images determined by window level and window width

RANGE OF HOUNSFIELD UNITS : 

RANGE OF HOUNSFIELD UNITS

Optimal window levels : 

Optimal window levels Mediastinum ,hilum and pleura: window width 350 to 500HU and window level of 30 to 50HU lungs: window width of 1000 to 1500HU and window level of -600 to -700HU Bones: window level of 30HU

Window width and window level : 

Window width and window level Any density greater than upper limit of window is displayed as white any below the is displayed as black Between these two displayed as shades of grey Median density is window level

Window level : 

Window level

Lung window : 

Lung window

Mediastinum window : 

Mediastinum window

Bone window : 

Bone window

Iv contrast : 

Iv contrast Because of high intrinsic contrast iv enhancement needed in special instances Increases attenuation number proportional to vascularity and permeability of tissue being measured Examples like emboli within pulmonary arteries, ,lymph nodes and inflammatory reactions

Effect of iv contrast : 

Effect of iv contrast

Adverse effects of iv contrast : 

Adverse effects of iv contrast Mild inconvenience such as itching to life threatening Anaphylactic reactions, renal toxicity, local tissue damage and delayed allergic reactions Dose dependent toxic reactions are nausea, vomiting ,flushing and renal failure

Hrct chest : 

Hrct chest Changed the approach to imaging in DPLD and airway disease Correlates closely with macroscopic appearance of pathological specimen Thin section and high spatial algorithm makes structures sharper and reduces image smoothing

Indications of ct : 

Indications of ct ABNORMAL CXR Further evaluation of mediastinal or pleural mass Assessment of thoracic aortic dissection Evaluation of patient with severe emphysema for lung volume reduction surgery

Indication of ct chest : 

Indication of ct chest Identify cryptic diffuse lung disease Detection of pulmonary metastasis Patient with biochemical or endocrine evidence of disease related to small intra thoracic tumors Patient with hemoptsis Pulmonary embolism

Radiation dose : 

Radiation dose Effective radiation dose of PA film is .15mSV One convention CT=50 PA HRCT=5-10 PA film

Normal thoracic anatomy on ct : 

Normal thoracic anatomy on ct

Thoracic anatomy : 

Thoracic anatomy

Normal thoracic anatomy : 

Normal thoracic anatomy

Appearance of bronchus : 

Appearance of bronchus Appearance of bronchi and vessels depends on their orientation Bronchus which course horizontally with plane of CT are seen along their long axis 1.RIGHT AND LEFT UL BRONCHUS 2.ANTERIOR SEGMENTAL BRONCHUS OF BOTH UPPER LOBES 3.POSTERIOR SEGMENT BRONCHUS OF RIGHT UPPER LOBE 4 .MIDDLE LOBE BRONCHUS 5.SUPERIOR SEGMENTAL BRONCHUS OF BOTH LOWER LOBE

Bronchial anatomy : 

Bronchial anatomy

Bronchial anatomy : 

Bronchial anatomy

APPEARANCE OF BRONCHUS : 

APPEARANCE OF BRONCHUS BRONCHUS LIE OBLIQUE ARE 1.LINGULAR BRONCHUS 2MEDIAL AND LATERAL SEGMENTAL BRONCHUS 3.SUPERIOR AND INFERIOR LINGULAR BRONCHUS.

APPEARANCE OF BRONCHUS : 

APPEARANCE OF BRONCHUS Accurate assessment of size of small parenchyma requires display level-450 HU Conventional CT :lobar bronchus and 70% of segmental bronchus HRCT: smaller bronchus and to distinguish vein and artery Limit of CT visibility is 1.5 to 2mm diameter airway with .2mm wall thickness

Appearance of pulmonary vessels : 

Appearance of pulmonary vessels Outer wall of pulmonary vessels sharp and smooth interface with lung Central pulmonary vessels are identified easily Arteries lie adjacent to bronchus Veins course to hilum Peripheral vessels require HRCT

Pulmonary vessels : 

Pulmonary vessels

Pulmonary vessels : 

Pulmonary vessels

Pulmonary artery : 

Pulmonary artery

Pulmonary vessels : 

Pulmonary vessels Diameter of main pulmonary artery:28.6mm Left main pulmonary artery:28mm Right main pulmonary artery:24mm Inner bronchial diameter to pulmonary diameter:0.65;if >1 bronchiectasis.

Pulmonary hypertention : 

Pulmonary hypertention

Interlobar fissure : 

Interlobar fissure MAJOR FISSURE 1.single line 2.fuzzy ill defined band 3.two parallel lines Morphology like propeller blade Upper thorax: lateral facing orientation Inferior thorax: medial facing orientation

Major fissure : 

Major fissure

Major fissure : 

Major fissure

Major fissure : 

Major fissure

Minor fissure : 

Minor fissure

Pulmonary ligament : 

Pulmonary ligament

Pulmonary ligament : 

Pulmonary ligament

Parenchyma and Interlobar septa : 

Parenchyma and Interlobar septa Attenuation of parenchyma depends on relative proportion of blood,gas,extravascular fluid and pulmonary tissue Normal lung parenchyma has fairly homogenous attenuation greater than air HRCT:interlobar septa is thin straight lines 1-2cm in length and .1mm in thick

parenchyma : 

parenchyma

Interlobar septa : 

Interlobar septa

Inter lobar septa : 

Inter lobar septa

Lymph node : 

Lymph node

REGIONAL LYMPH NODAL STATION : 

REGIONAL LYMPH NODAL STATION

Lymph node : 

Lymph node Lymph node vary in size according to location Short axis measurement is better

Lymph node size : 

Lymph node size

Nodal enlargement : 

Nodal enlargement 54 yr old female with biopsy proved non specific interstitial pneumonia with enlarged station 7 node<sub carina node >

Mediastinum : 

Mediastinum Lines,stripes,and interfaces. Lines. 1.Anteriorjunctional line 2.Posterior junctional line 3.paraspinal line Stripes . 1.right and left paratracheal stripes Interfaces .1.azygoesophageal interface 2.descending thoracic interface

mediastinum : 

mediastinum

Anterior junctional line : 

Anterior junctional line

Junctional lines : 

Junctional lines

Azygoesophageal interface : 

Azygoesophageal interface

Thoracic inlet : 

Thoracic inlet

Mediastinum : 

Mediastinum

Mediastinum : 

Mediastinum

Mediastinum : 

Mediastinum

Mediastinum : 

Mediastinum

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