Diagnostic Imaging
Learn the importance of collaboration with imaging departments, radiation protection principles, advantages of different imaging techniques, and how to choose and interpret imaging for accurate diagnoses. Explore the hazards of imaging and precautions for patients with renal impairments.
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Presentation Transcript
Diagnostic Imaging Objectives At the end of this lecture the students should be able to understand: The advantages of good working relationships and close collaboration with the imaging department in planning appropriate investigations. The basic principles of radiation protection. The principles of different imaging techniques and their advantages and disadvantages in different clinical scenarios.
Diagnostic Imaging Introduction: History and Clinical Examination Investigations Correct Diagnosis Appropriate surgical management Imaging
Diagnostic Imaging How and what to choose ? - Simplest and cheapest test hoping it will answer the question - Know the limitation and complication of each test. - Availability, experience, and cost in addition to clinical presentation.
Diagnostic Imaging How to request imaging ? Collaboration between the radiologist and the referrer What do you want to know ? State the clinical problem. Give provisional diagnosis. If you are not sure about the best method to reach the diagnosis, consult and discuss the problem with the radiologist. Some information are of value (past medical Hx., drugs, LMC)
Diagnostic Imaging Interpreting Images:
Diagnostic Imaging Hazards of Imaging: Contrast media: (low osmolarity contrast media) LOCM X HOCM(high osmolarity contrast media) Allergic reaction and nephrotoxicity 5-10 times safer. Serious reactions 1:2500 cases. Life threatening reactions 1:25000 cases. No difference in the risk of sudden death. Allergic reaction time and treatment. early, steroid
Diagnostic Imaging Patients with renal impairments: (DM) - Get a recent creatinine and urea level. - Risk X Benefit - Minimal dose of LOCM. - Patient well hydrated. - N- acetylcysteine for renal protection. - Metformin Lactic acidosis.(stop / 100ml of contrast / normal renal function) Gadolinium containing contrast ?? - Allergic reaction is rare (mild 1:200 sever 1:10000) - Nephrotoxic (pre-existing renal disease) - NSF - C/I : neonate, RF, liver transplantation, and pregnancy.
Diagnostic Imaging Hazard of Ionizing radiation. (15% of total human radiation) Predictable, dose dependent tissue effects lens (cataract) , chronic exposure to radiation All or nothing effects (stochastic) cancer , not dose dependent, but increased in likelihood with increased radiation dose. CT examination of abdomen and pelvis Cancer risk 1:1000 Plain films (chest and limbs) Cancer risk 1:1000000
Diagnostic Imaging - Fluoroscopy and portable machines use much more radiation to achieve the same result and possibly lower quality. - When using the image intensifier, lead aprons, thyroid shields, lead glasses and radiation badges should always be worn. - Pregnancy in the female patient or staff must be excluded
Diagnostic Imaging Conventional radiography - Roentgen 1895. - Chest, trauma, orthopaedics. - Depends on the degree of tissue absorption of the X ray emitted from the machine (Black and White). - Air, fat, soft tissue, bone and mineralization, and metal. - Advantages: Cheap Available Easily producible and comparable Relatively low dose of radiation
Diagnostic Imaging - Disadvantage : Lack of soft tissue differentiation. To overcome this problem: Use of contrast materials Fluorescent screen
Diagnostic Imaging Ultrasound: - High frequency sound waves (3-20MHz) generated by a transducer. - Time and direction of waves reflection will generate an image. - High frequency greater resolution. Less penetration. Abdomen 3-7 MHz for superficial structures (high frequency) - Endocavitary transducers e.g. transvaginal, transrectal, endoscopic
Diagnostic Imaging Reflection of US waves from a moving objects (RBCs) Change in frequency of US waves Measure these changes Speed and direction of movement Principles of Doppler US
Diagnostic Imaging Advantages of US: Cheap Easily available - Assessment of liver, biliary system, and renal tract. (1stline invest.) - Gynecology and Obstetric. - Thyroid and testicles (High frequency transducer). - Interventional radiology by using the needle for biopsy and drainage. - Soft tissue foreign bodies. - Ligament, tendon, and muscle injuries.
Diagnostic Imaging Disadvantages of US: Highly operator dependent Difficult in getting images to areas beyond bony or air filled structures. Images can not be reliably reviewed away from the patient. Needs a long learning curve in some area of expertise. Resolution depends on available machines.
Diagnostic Imaging Computed tomography (CT): A great development in CT technology in the last 30 years. Conventional Helical Spiral Multidetector machine. Gantry containing X ray tubes, filters, and detectors. Revolves around the patient acquiring information at different angles and projections. The information is mathematically reconstructed to obtain 2D images.
Diagnostic Imaging Higher contrast resolution than conventional radiograph. Assessment of different phases (early and late) (arterial and venous). Used in thoracic, abdominal, neurological, muscloskeletal , and trauma imaging. CT angiography. Virtual colonoscopy and bronchoscopy. 3D image aiding in surgical planning.
Diagnostic Imaging Disadvantages: Cost High dose of radiation CT abd. & pelvis = 500 CXR
Diagnostic Imaging Magnetic resonance imaging (MRI): Integral part of imaging arsenal with expanding indications. Nuclei have an odd number of electrons or protons that have a characteristic movement in a magnetic field (precession) producing a magnetic moment as a result of this motion. Applying a strong magnetic field by the MRI result in alignment of these nuclei within the magnetic field producing a magnetic moment. A radiofrequency pulses is then applied to alter the nuclei motion. Once the radiofrequency pulses removed, the nuclei realign themselves with the main magnetic field (relaxation). During this time they emit a radiofrequency signals that recorded to produce image. Tissue characteristics define the manner and rate at which nuclei relax.
Diagnostic Imaging Nuclear medicine: Radioactive element or radionuclide are used in addition to ionizing radiation. Gallium, Technetium, Thallium, and iodine are examples of radioactive substances. A detector such as gamma camera used to detect and localize the emission of these radioactive elements from the patient. Each substance had an affinity to certain tissue.(large no. of elements) Nuclear medicine provides functional status of the system.
Diagnostic Imaging Bone imaging metabolic diseases metastatic diseases arthropathy occult infection traumatic injury obstruction renovascular hypertension renal transplant Genitourinary system Dynamic study (function and perfusion)
Diagnostic Imaging Thyroid and parathyroid Cardiac diseases(ischemia) Pulmonary embolism. Inflammatory bowel diseases. Occult infection. Positron emission tomography (PET) 18F , metabolic characters of tissue. Cost, very limited availability, and relatively low spatial resolution (PET/CT)
