The Importance of Imaging How do you order the right study to correctly assess what you’re looking for.
Understanding different modes • Radiology is becoming more and more important in the diagnosis and treatment of patients • Imaging the human body requires the use of different types of focused energies to separate the different tissues in the body and distinguish healthy tissue from disease.
The Different Energies • Plain X-ray • Fluoroscopy • Angiography • Ultrasound • Computed tomography • Nuclear Medicine • PET-CT • Magnetic Resonance
Plain Film Radiography • X-rays are ionizing, extremely short wavelength and high energies. • X-rays travel through the body and can be absorbed or scattered. Contrast images depend on tissue densities. • Most X-ray systems now use digital acquisition. • Main applications are thorax, abdomen, and skeletal systems especially in trauma.
Plain X-ray
Fluoroscopy • Historically the first method of imagining dating back to 1895. • Fluoroscopy has a role in both diagnostic and procedural work, including vascular intervention and use in operating theaters. • Orthopedist use in aligning fixation devices and reducing fractures. • Radiologist use them in arthrograms and injections.
Fluoroscopy • Contrast agents central in GI and Urologic evaluations. • Positive agents such as barium and iodine block X-rays and pathology appears as filling defects within the contrast. • Negative agents such as air and water distend structures and lumens and allow more X-rays through.
Fluoroscopy • Double contrast techniques utilize both to allow surface to be visualized in detail e.g. bowel mucosa.
GI Fluroscopy • Luminal contrast can be administered orally or rectally. • Swallow: pharynx and esophagus. • Meal: lower esophagus, stomach, and duodenal cap. • Small bowel meal: small bowel especially the terminal ileum. • Single contrast water soluble: upper and lower obstruction and perforation.
GI Fluoroscopy • Double contrast enema: colonic pathology, excellent mucosal detail but not in acute colitis or diverticulitis. • Biliary imagining: including endoscopic retrograde cholangiopancreatography (ERCP). • Procedures: nasogastric tube, G-tube, esophageal and colonic stents.
Urological Fluoroscopy • Nephrostomy insertion and evaluation. • Ureteric stint placement and evaluation. • Cystograms and urethrograms. • Retrograde urethrograms. • Loopograms or conduitograms to evaluate neo-bladder after urinary diversion surgery.
Ultrasound • Ultrasound uses high-frequency sound waves and the way they travel through the body. • Tissues of different densities reflect sound waves back to the probe with their own characteristics. These variances are used to create an image. • Ultrasound waves are reflected by bone and gas and are poor for imaging these structures.
Ultrasound • The procedure is operator sensitive and is the first line of investigation in biliary, cardiac, renal, obstetrical, and many vascular procedures. • US is frequently used in guiding biopsies, aspirations, and insertions of drains. • Doppler US allows assessment of patency and flow in blood vessels.
Abdominal US • The investigation of solid organs of the abdomen (liver, GB, pancreas, aorta, kidneys, spleen). • Liver size , texture, and masses. • Biliary system: bile duct distention, GB stones and wall thickness. • Doppler of hepatic artery/veins and portal flow characteristics.
Abdominal US • Pancreas: size, texture, swelling, tumors. • Aorta: assessing diameter of aneurysm. • Kidneys: size, texture, presence of calculi and size of collecting system (hydronephrosis). • The bladder is not routinely examined and a dedicated renal scan should be requested. • Spleen: size and texture (calcifications, ruptures.
Abdominal US
Urinary US • Dedicated urinary tract scans: full bladder scans to assess bladder wall thickness, hydronephrosis. • Pre and post-micturation to assess bladder capacity and emptying.
Pelvic and Testicular US • Trans abdominally with full bladder: establishing early pregnancy or miscarriage, thickness of endometrial stripe, leiomyoma. • Transvaginal: Gives greater detail of pelvic organs and early pregnancy.
Testicular US • Tumors, enlargement • Hydroceles • Inflammation/infection • Doppler evaluation of blood flow (torsion)
Neck US • Evaluate neck and thyroid masses. • Lymph node characteristics.
Cardiac US • 2D echocardiography: evaluation of chamber size, wall thickness, anatomy and motion. • Duplex Doppler: Evaluation of blood flow, valve competence, spatial relationships.
Vascular US • Assessment of: • Carotid artery disease • Peripheral vascular disease • Venous imaging.
Computed tomography • Computed tomography uses X-rays to produce cross-sectional images of the body. Images are generated by the rotation an X-ray tube around the body. A ring of detectors surrounding the body measures the transmitted radiation. The numerical data is reconstructed in a computer and assembled into an image. In spiral machines the scanning X-ray is moved along the stationary table.
CT • Fast CT scan “slices” can be manipulated into 3D images that can then be manipulated by computer. • Contrast media of barium or iodine can be used both orally and intravenously to opacity structures and vascularity.
CT • Drawbacks to CT are heavier doses of radiation than other modalities, cost, and risk of intravenous contrast to kidney function. • Some areas of the body are imaged poorly including the spine and posterior fossa.
Nuclear Medicine • Nuclear medicine differs from other forms of imaging in that it shows the physiological function of a system rather than an anatomical region. • Radioactive isotopes permit detection by emitting gamma radiation which is detected by a gamma camera. Pathologic conditions may lead to increased uptake (hot spots) or decreased uptake (cold spots).
Nuclear Medicine • The commonest radionucleotide is technetium 99, a manufactured and has a half life of 6 hours. • When a radionucleotide is coupled with a drug it is called a radio-pharmaceutical. The pharmaceutical is chosen to rapidly localize the intended target. The radionucleotides are injected intravenously, ingested orally, or inhaled.
Nuclear Medicine • The gamma camera consists of a large array of radio-detectors. Gamma rays striking the elements are converted to light photons which can be displayed on a cathode ray tube and recorded. • The image is acquired in multiple planes while the patient sits or lies still. The images may be static or multi-frame and recorded over time.
Nuclear Medicine • Disadvantages of nuclear scanning is they require long periods of motionless scanning and many times continued scanning at later times, so the exam can in some cases take hours.
Nuclear Medicine • Indications for nuclear scanning are: • Bone scan: infection, occult fracture, bone metastasis. • Myocardial perfusion scan: SPECT (nuclear stress test). • Thyroid uptake scan: for “hot” and “cold lesions.
Nuclear Medicine • Renal scanning: static images for renal functioning and scarring. Dynamic imaging for perfusion excretion and renal vascular HTN. • Ventilation/ perfusions scan: intravenous isotope combined with inhaled isotope for pulmonary embolus exclusion. • Contraindications: radiation dose must be weighed against other modalities in children, pregnancy and breast feeding.
Nuclear Medicine • Advantages: Demonstrates physiology. Widely available, relatively cheap. • Disadvantages: Radiation dose (pt. continues to emit radiation after study, poor spatial resolution, time consuming. • Certain types of scans require preparation, stopping meds, fasting, or pre-dosing. Check with local providers for details.
PET-CT • PET-CT (positron emission tomography) is relatively new technique of rapidly increasing in usage. The patient undergoes PET and CT simultaneously and the results are merged giving functional information of radioisotope and accurate anatomical detail of CT. • Radio tracer isotope 2-18 fluorodeoxy-D-glucose (FDG) is injected IV. The tracer accumulates in areas of high intracellular metabolism. Tumor cell are highly reactive and retain the tracer longer.
PET-CT • Patient Preparation: fasting 4-6 hours, glucose checked prior to testing, injection given and patient rests quietly while the isotope circulates. Scanning begins 60 min after injection, proceeds for 30-90 min. Images are obtained from the top of the head to mid thigh with arms above head. CT proceeds after the PET, Scanner and CT are in the same gantry so patient remain on same table.
PET-CT • Indications: Better at detecting distant metastasis of wide variety of tumors. Used for complete staging in cases cases where traditional testing suggest local disease. PET used in assessing the response to chemotherapy and recurrence. Developing roles in neuro-imagining and heart perfusion. • Relative contraindications: Pregnancy, uncontrolled DM make interpretation difficult. • Patients must lie flat for considerable time.
Pet CT
PET-CT SCANNERS
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