Ct Imaging Techniques Rad 311 PDF

CT Imaging Techniques RAD 311 Dr. Khalid.Hassan [email protected] The suprahyoid neck is divided into : - Nasopharynx. - Oropharynx. - Oral cavity. CT of the neck Indication  (1) Screening and staging of tumours or adenopathies.  (...

CT Imaging Techniques RAD 311 Dr. Khalid.Hassan [email protected] The suprahyoid neck is divided into : - Nasopharynx. - Oropharynx. - Oral cavity. CT of the neck Indication  (1) Screening and staging of tumours or adenopathies.  (2) Detection of parotid gland pathology.  (3) Detection of carotid atheromatosis and obstruction.  (4) Evaluation of congenital or post traumatic abnormality. Patient Preparation * Fasting 4- 6 hours  Contrast material [ Urographin, Telebrix,…] 1-2 ml/kg - renal function tests  Anesthesia Children, Uncooperative patients Contrast material administration NO Traumatic cases, YES Cold cases [masses , inflammation , granulomas , …] SCANNING TECHNIQUES - Patient position supine - Technique - Scanogram [Lateral] from orbitometal line to vertex - gantry tilt - Scan intervals ( 5mm ) AXIAL  CT procedure :  Patient is supine.  The gantry should be angled to avoid streak artifact from dental hardware.  Slice thickness 3-5 mm or contiguous spiral, but for large lesions slice more than 3-5 mm.  WW and WL for optimal image display are:  Soft tissue : WL:50 , WW:400  Bone : WL:300 , WW :2000  The patient should be instructed to breath quietly and to suspend swallowing during data acquisition.  IV contrast biphasic. 1ml/sec for 50ml followed by 0.4 ml/sec for maximum injected volume of 100 ml Start scan 1 min after the beginning of injection. Indications for CTA of the carotid artery include:  Stenosis.  Occlusion.  Aneurysm.  Trauma. Advantages of spiral CT chest  Allows major portions or entire chest to be scanned during a single breath hold  Eliminates motion artifacts  High quality multiplanar, three dimensional image display  Basis of virtual bronchoscope 4  Some Indications of Chest CT Routine Chest CT 1. Evaluation of mediastinal or pleural mass 2. Detection of pulmonary metastasis 3. Patient with Hemoptysis 4. Abscesses or cysts 5. Guidance FNA 5 Some Indications of Chest CT HRCT Chest 1. Suspected COPD (e.g) - Atelectasis - Bronchitis - Emphysema - Asthma 2. Suspected infiltrative disease but normal or nonspecific CXR 3. Further characterize diffuse disease 4. CXR findings not in keeping with clinical findings 5. Guide type and site of biopsy 6 Patient Preparation and contrast Patient preparation: Fasting for 3-4 Hours before the examination Contrast: The use of contrast media which injected intravenously is important for visualization of structures within the mediastinum. Department protocols/radiologist preferences determine the specific type, volume and site of injection. ( Average dose 100ml) For children 2 ml per kilogram body weight. The advantage of contrast media : 1. To detect lesions 2. To distinguish vessels from lesions 3. To demonstrate displacement of vessels by masses 4. To demonstrate the enhancement of pathologies 7 CT Chest -Slice spacing  Adequate assessment of patient10 mm interval  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 8 CT Chest Protocols Optimization of the CT examination Requires:  Sufficient clinical information about the case from the referring physician  The Technologist should select the appropriate CT protocol based on careful review of relevant patient history and clinical indications as well as all prior available imaging studies. 18 CT Chest Protocols CHEST (Lungs and Mediastinum)  Assure patient Patient Preparation and Care?  Procedure explanation and instructions  Dress  Supine arms elevated above head ( Head Patient Positioning? or feet first) Topogram (Scanning volume)?  From lung apices to below diaphragm  Breath hold in inspiration Breathing Instructions? (single breath hold) 19 CHEST ( Lungs and Mediastinum) Indications General screening of Pathology Patient Position Supine arms elevated above head Topogram From lung apices to below diaphragm Breathing Breath hold in inspiration ( single breath hold) Contrast I.V : 100 ml at 3ml/s. Imaging timing about 30-45 s. Technical Parameters  Slice thickness : 7-10mm  (3-5 mm for small lesions) Filming Mediastinum widow and Lung widow Parameters Bone window if needed Comments For the demonstration of lung nodules a low dose protocol with out contrast enhancement is recommended. 20 CHEST ( HRCT)  Thin section and high spatial algorithm makes structures sharper Indications lung diseases e.g. :-(Bronchiectasis, Fibrosis, Emphysema etc.) Patient Position Supine arms elevated above head Topogram From lung apices to below diaphragm Breathing Breath hold in inspiration ( single breath hold) Contrast N/A Basic Technical Slice thickness: 2-3 mm Parameters Windowing  Lung widow Comments  Prone scans – to differentiate atelectasis  Expiratory scans – to show air trapping 21 CHEST ( HRCT) CT of The Airways ( key Concepts) 23  low-dose high resolution HR lung protocol  This protocol is designed to serve as a routine protocol (soft and lung window).  Demarcation of the esophagus is optimized when giving a swallow of barium suspension shortly before initiation of the scan.  For screening, detection, or exclusion of pulmonary nodes or infiltrates only, a low-dose high resolution HR lung protocol is recommended:  low-dose high resolution HR lung protocol  – Collimation: 4x2.5 mm  – Pitch factor 1.5  – Reconstruction: 3 mm  – Scanner setting: 120 kV, 10–20 mAs  – Rotation time: 0.5–0.75 s  – Kernel (algorithm): lung  – Window: lung window 1,500/–600 28  low-dose high resolution HR lung protocol  Administration of contrast material is not necessary.  This protocol drastically reduces the dose of the CT scan at the expense of more noise.  To detect or exclude asbestosis or orthostatic changes, an additional scan of this protocol in the prone position is recommended.  ECG triggering may be used in selected cases to minimize motion artifacts 29 Advantages of spiral CT chest Virtual bronchoscopy  Virtual Bronchoscopy (VB) is a 3 dimensional, computer-generated technique that produces endobronchial images from spiral CT data. (McAdams et al AJR 1998).  A spiral CT scanner acquires continuous images of a patient’s body thus providing imaging data between actual slices displayed. Overlapping slices can be reconstructed from the raw data set & high quality 2D and 3D reconstructions can be created.  Advances in computer technique have allowed automatic creation of a 3D tracheobronchial tree model from CT scan images of the chest.  The viewer can then navigate through the inside of the tracheobronchial tree as if in a simulated or virtual bronchoscopy (VB). 31 Virtual bronchoscopy (Some Potential applications)  Educational  Pre- bronchoscopy planning  Appraisal of central airways  Guide to peripheral airways  Pre op planning  Interventional- Tracheobronchial stent placement 32 35