Medical imaging X-ray, CT, MRI, scintigraphy, SPECT, PET Györgyi Műzes Semmelweis University, 2nd Dept. of Medicine
Medical imaging: definition technical process of creating visual representations about the interior of the body for clinical analysis and medical intervention visual representation on the function of some organs or tissues Aims: to reveal internal structures for diagnostic, therapeutic and pathologic purposes to establish a database of normal anatomy and physiology
Medical imaging: modalities - X-ray radiography - computed tomography scan (CT) - magnetic resonance imaging (MRI) - nuclear medicine functional imaging techniques - scintigraphy - single-photon emission computed tomography (SPECT) - positron emission tomography (PET) - thermography - ultrasonography, elastography - endoscopy
X-ray radiography projection radiography (x-ray) aims: to determine the type and extent of bone lesions (e.g. fracture), or to detect pathological changes in the lungs with the use of radio-opaque contrast media (e.g.: barium), helps to visualize the structure of the GI tract fluoroscopy (with or without catheter guidance) produces RT images of internal structures, but employs a constant input of low dose x-rays the use of contrast media (barium, iodine, air) helps to visualize functioning internal organs it is used in image-guided procedures when constant feedback during a procedure is required (e.g.: catheter techniques)
Computed tomograpy scan (CT scan) computer-processed combinations of many X-ray measurements taken from different angles to produce cross-sectional (tomographic) images (virtual "slices") of specific areas of a scanned object digital geometry processing is used to further generate a 3D volume of the inside of the object from a large series of 2D radiographic images
CT scan completely eliminates the superimposition of images of structures outside the area of interest inherent high-contrast resolution: differences between tissues -that differ in physical density by less than 1%- can be distinguished multiplanar reformatted imaging is available main adverse effects: radiation-induced carcinogenesis contrast reactions
applications head CT scan infarction, tumors, calcifications, haemorrhage, bone trauma lungs acute and chronic disorders, tumors pulmonary angiogram pulmonary embolism cardiac coronary CTA abdominal and pelvic extremities
Hydrocephalus Brain metatases
Magnetic resonance imaging (MRI) uses powerful magnets to polarize and excite hydrogen nuclei of water molecules in human tissue, producing a detectable signal which is spatially encoded, resulting in images of the body the MRI machine emits a radio frequency (RF) pulse at the resonant frequency of the hydrogen atoms on water molecules RF coils send the pulse to the area of the body to be examined RF pulse is absorbed by protons, and when the RF pulse is turned off, the protons "relax" back to alignment with the primary magnet and emit radio-waves the radio-frequency emission from the hydrogen-atoms on water is what is detected and reconstructed into an image
MRI MRI creates a 2D image of a thin "slice" of the body 3D imaging is also available T1 and T2 weightening each tissue returns to its equilibrium state after excitation by the independent processes of T1 (spin-lattice) and T2 (spin-spin) relaxation to create a T1-weighted image, magnetization is allowed to recover before measuring the MR signal by changing the repetition time T1 imaging is useful for assessing the cerebral cortex, identifying fatty tissue, characterizing focal liver lesions and in general for obtaining morphological information to create a T2-weighted image, magnetization is allowed to decay before measuring the MR signal by changing the echo time T2 weightening is useful for detecting edema, inflammation, revealing white matter lesions and assessing zonal anatomy in the prostate and uterus
MRI applications neuroimaging demyelinating diseases, dementia, cerebrovascular disease, infectious diseases, epilepsy, CNS cancers, MRI-guided stereotactic surgery, radiosurgery cardiovascular myocardial ischemia and viability, cardiomyopathies, myocarditis, iron overload, vascular diseases, congenital heart diseases musculoskeletal spinal imaging, joint diseases, soft tissue tumors liver and gastrointestinal hepatobiliary disorders, IBD, CRC angiography
MRI specialized configurations magnetic resonance spectroscopy real-time MRI interventional MRI magnetic resonance-guided focused ultrasound multinuclear imaging molecular imaging by MRI
MRI safe potential health risks: tissue heating from exposure to the RF field and the presence of implanted devices (e.g.: pacemakers, joint implants) injuries: due to failed safety procedures or human error Contraindications cochlear implants, cardiac pacemakers, shrapnel, metallic foreign bodies in the eyes the safety of MRI during the first trimester of pregnancy is uncertain expensive, time-consuming, and claustrophobia-exacerbating technique
Brain tumor
AS right ilium: erosion which extends across the entire joint surface
MR angiography
Scintigraphy diagnostic test in nuclear medicine radioisotopes attached to drugs are uptaken by a specific organ or tissue (radiopharmaceuticals) emitted gamma radiation is captured by gamma cameras to form 2D images
Indications: Scintigraphy biliary system (cholescintigraphy) gall stone, tumor, fistulas, functional disorders lungs (pulmonary embolism, right-to-left shunts) bone (fractures, tumors) heart (coronary steal, ischemic coronary artery disease) thyroid / parathyroid glands (adenomas, metastasis, function) renal / urinary system (renal artery stenosis, obstructions) full body Ga-, In white blood cell-, iobenguane- (MIBG), octreotide scan function tests (urea breath test)
99m Tc-MDP bone scintigraphy: multi-focal increased uptake (skeletal metastases from renal carcinoma)
Single-photon emission computed tomography (SPECT) - similar to scintigraphy, but provides true 3D information - radionuclide is injected into the bloodstream, than binds to certain types of tissues - SPECT scan monitors level of biological activity in the analyzed 3D region
SPECT: imaging Applications: - tumors - infections (leukocyte) - thyroid - bone scintigraphy - myocardial perfusion (ischemic heart disease, cardiac stress test) - functional brain (cerebral blood flow, dementia, Alzheimer s disease, cognitive testing) - SPECT/CT: gamma camera operates with a CT scan
Myocardium
Dementia: Alzheimer s; vascular
Positron emission tomography computed tomography (PET-CT) - the functional imaging obtained by PET depicts the spatial distribution of metabolic or biochemical activity in the body - this functional imaging is correlated with anatomic imaging obtained by CT scanning - 2D and 3D image reconstructions are available - radioactive fluorine-18 is commonly used to trace glucose metabolism (fluorodeoxyglucose, FDG)
PET-CT Applications - oncology (diagnosis, staging, follow-up) - neuroimaging (amyloid, cognitive neuroscience, schizophrenia, stereotactic surgery) - cardiology (hibernating myocardium) - infectious diseases (infection-associated inflammatory response) - pharmacokinetics - musculo-skeletal imaging (activating of deeper lying muscles)
GIST tumor
Infrared thermography (IRT) for determining areas of the body that have irregular blood flow non-contact method commonly used by sportphysicians to determine areas of the body that have inflammation some alternative medicine practitioners use it to diagnose cancer (!), although it is ineffective for this purpose
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