VASCULAR IMAGING WITH Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) scanning requires the use of a very strong magnetic field but does not use ionizing radiation. The magnet is contained in the housing of the scanner and creates a magnetic field oriented down the bore of the magnet. The patient is placed within the magnetic field by lying on a table which is placed through the center of the opening of the magnet. The strength of the magnetic field is measured in units called gauss or Tesla: 10,000 gauss equals 1 Tesla. The earth's magnetic field is approximately 0.6 gauss. Most MRI scanners contain superconducting magnets with a field strength of approximately 1.5 Tesla. In superconducting magnets, the wire conducts the current without resistance because it is cooled to a temperature close to absolute zero (4 K) by being bathed in a jacket of liquid helium. The electrical current flows continuously around many loops, creating the required magnetic field.
The physics of MRI are extremely complex, and only an extremely simplified explanation is given. When a patient is placed within an MR scanner, the protons in the patients tissues (primarily protons contained in water molecules) will tend to align themselves along the direction of the magnetic field. A radio-frequency electromagnetic pulse is then applied, which deflects the protons off their axis along the magnetic field. As the protons realign themselves with the magnetic
field, a signal is produced. This signal is detected by an antenna, and with the help of computer analysis, is converted into an image.

The process by which the protons realign themselves with the magnetic field is referred to as relaxation. The protons undergo two types of relaxation: T1 (or longitudinal) relaxation and T2 (or transverse relaxation) relaxation.
Different tissues undergo different rates of relaxation, and these differences create the contrast between different tissues. T1-weighted images emphasize the difference in T1 relaxation times between different structures. In these images, watercontaining
structures are dark. Since most pathologic processes (such as tumors, injuries, CVA's, etc.) involve edema (or water), T1-weighted images do not show good contrast between normal and abnormal tissues. However, they do demonstrate excellent anatomic detail. T2-weighted images emphasize the difference in T2 relaxation times between different tissues. Since water is bright on these images, T2-weighted images provide excellent contrast between normal and abnormal tissues, although the anatomic detail is less then that of T1-weighted images. Figure bellow shows a typical T1-weighted image. Figure 12 shows the difference between T1 and T2-weighted images.

Intravenous contrast is often used to improve the sensitivity of MR imaging, especially in the brain and spine.
MR contrast agents contain gadolinium, which increases T1 relaxation and causes certain abnormalities to “light up” on T1-weighted images. These agents contain no iodine, and allergic reactions are extremely rare. MRI images can be obtained in any imaging plane without moving the patient. The three standard views usually used
1. Transverse (axial): viewed as if standing at the patient's feet (similar to standard CT).
2. Coronal: Viewed from the front.
3. Sagittal: Viewed from the side.

MR angiography (MRA) permits imaging of the blood vessels in several parts of the body. The most frequent vessels studied include the Circle of Willis (and its main branches) in the brain and the carotid bifurcation in the neck.

The basic principle is that special pulse sequences are used by the MR scanner which causes flowing blood to appear very bright and all stationary tissue to appear very dark. If arterial structures are being studied, additional pulses are applied to erase the signal in veins. Multiple slices are obtained at adjacent levels through the region of interest. A computer then stacks these images on top of each other and creates a 3-D
image similar in appearance to a contrast angiogram, although no contrast agent is used. The constructed images can be rotated 360 degrees so that the vessels can be studied in all projections. Figure below is an example of the raw images created by the scanner. Note that the vessels are bright and all of the surrounding tissues are dark.


Although multiple studies have been performed, no significant permanent biological hazards have been demonstrated as a result of exposure to patients from the magnetic fields or radio-frequency electromagnetic pulses used in magnetic resonance imaging. However, there can be adverse effects on various medical devices implanted into patients and therefore all patients must be carefully screened to determine if MR
scanning can be safely performed. Potential risks include the following:
1. Cardiac pacemakers: Absolute contraindication. These patients cannot be scanned.
2. Cerebral aneurysm clip: Unless there is documented proof that a non-ferromagnetic clip was used, these patients cannot be scanned.
3. Metal fragments in body (bullet, BB, shrapnel, etc.): Safe, unless in contact with vital organ, such as heart, spinal cord, eye.

4. Surgical clips: Safe. Flow and Atherosclerosis (Research Topic) There appears to be a relationship between the hemodynamics of blood flow (details of the fluid flow such as
shear) and the progression of vascular disease. Unfortunately, only simple flow factors such as velocity can be measured in vivo (e.g. with MRA) while the important hemodynamic factors cannot. One way around this problem is to use MRI to determine the size and shape of an artery (or, for example, the carotid bifurcation which is a common location for vascular disease), MRA to determine the pulsatile velocity at the input and output of the vessel, and to use a computer to simulate the actual flow pattern through the vessel so as to match the input and output conditions.

calculated flow pattern through the carotid artery of a healthy
volunteer. The regions of high shear can be determined in this
calculation. In the future, it may be possible to perform this
calculation and identify patients with an elevated risk of
atherosclerotic plaque development.

Figure demonstrates image_thumb[8]

the appearance of the MRA. The same data is used to create sagittal, transverse and coronal images

Radiology Information Tags:

Artikel Terkait

VASCULAR IMAGING WITH Magnetic Resonance Imaging (MRI)
4/ 5


Suka dengan artikel di atas? Silakan berlangganan gratis via email

This below all content of radiology information

Neuroradiology Musculoskeletal radiology MRI Musculoskeletal MRI Abnormal Mri Brain X-RAY differential diagnosis Head Neck Anatomy mnemonic CT Teleradiology Radiology News chest Radiology musculoskeletal salary pediatrics ultrasound ultrasound images job Brain tumour abdomen interventional radiology Apk Android CT Abdomen with contrast DAMS Imaging radiology ramblings residency c nature pediatric radiology random ramblings xray C T Radiology Top basics body imaging guide procedure web 2.0 Chest X Ray Interpretation Teleradiology Providers head and neck radiology video Fun Ultrasound Hepatitis b cancer chest radiology salary 1 CXR GenitoUrinary ORTHOPEDICS Sonographic Measurements Stroke dams md/ms coaching mammography radiology business tuberculosis BRAIN Clinicoradiological series FETUS GI radiology Gastrointestinal x ray Radiology 4 Radiology Conferences Radiology Images Telemedicine UPPER LIMPS Ultrasound in Emergencies dynamic MRI lifestyle radiology links renal case spine 3 tesla MRI Dams clinicoradiological series Entrepreneur Gastrointestinal Tract Images Literature Liver abscess ultrasound MD/MS coaching Radiology 40 Radiology Imaging Radiology Journal Radiology PDF Radiology mcqs Ultrasound Technique blog bone tumour cardiac CT career cerebral venous thrombosis chest xray d fracture gadolinium gastrointestinal genitourinary radiology hepatobiliary imaging lipoma medical blogs mri lower abdomen pelvis psychiatry radiation concern social networking technology training urogenital imaging weblog 3D CT Arachnoid cyst CT Cardiac Chest X Ray Diploma Guid Equipment Cost FDA Fibrous dysplasia Interventional Ultrasound Guiding Biopsi MDCT MR Pancreas MRI Vertebrae MRI Vertebrae lumbal MRI contrast MRS RTA Radiology Teaching resource TB Hip TECHNIQUE Tech Thorax X Ray Upper Ext aiims ankle sprain bowel cancer brain abscess case study computers and radiology contrast ependymoma epidermoid facebook guest post internet journal of radiology iphone kienbock disease liver liver segments ct locum tenens mri abdomen multislice CT pericallosal lipoma plain film teaching files private practice radiology humour shoulder arthrogram shoulder dislocation small bowel social media trigeminal neuralgia tuberous sclerosis venous x ray Vertebrae 3d printing 7 tesla MRI ACL reconstruction ACL tear ACLS AIIMS nov 2008 ALPSA lesion ANGIOGRAPHY ATFL B12 deficiency BLS BOLD Breast imaging Breast imaging Mammography CHF CT Paranasal CT Scanner Price CT angiography CT coronary angiography CT technology CV junction CXR teaching files Carcinoid Contrast Agent Creutzfeldt-Jakob Disease Dams MD/ms Dams grand rounds Diffusion weighted imaging Dysmenorrhea E E World Award 2011 EYE Embolization Imaging Entrepreneurship FMG India FMGE FNH Focal liver lesions ultrasound Focal nodular hyperplasia GBM GI Gall bladder Glioblastoma multiforme Glomus jugulare HEAD HEART HRCT HSG Head injury ICA dissection IRIA 2011 IUGR IVC filter Iliotibial Band Friction Syndrome Job Info Kidney Cancer LV thrombus Leptomeningeal cyst MAMOGRAPHY MCI Screening MD MPPG MR mammography MR urography MRA MRCP MRI Cervical MRI update MRI/PET MRV Mesenteric ischemia Middle East respiratory syndrome coronavirus (MERS-CoV) Motor neuron disease NECK Normal Liver US Oncology trial PDF Radiology PM and R Physician PNS Partial anomalous pulmonary venous drainage Persistent trigeminal artery Pg entrance Physiatrist Physiatry Physician Assistant Plastic Surgery Price MRI Machines 2017 Pulmonology Pulvinar sign Radiology Price List Radiology Today Radiology Updates Radiology grandrounds Radiology images of GI Tract Renal Ultrasound Retinal Surgery Rheumatology Ryles tube SKULL Seizure Sellar Masses Sleep Medicine Sports Medicine Subdural hematoma Surgery TBM TRIANGULAR FIBROCARTILAGE COMPLEX Trauma Surgery URI Ultrasound HIV Umbilical vein Update Article Upper Extremity X Ray Urology Usmle VHL Vascular Surgery Veteran Affairs X Ray Head about accessory bone acute cerebillitis acute pancreatitis aiims may 2011 aipg ankle ankle fracture apple articular cartilage aspergilloma atherosclerosis avulsion injury awards bankart lesion basilar artery thrombosis bilateral phaeochromocytoma biopsy bipolar bohler's angle bone tumours brachial plexus brain tb brainstem stroke branchial cyst breast cancer screening buford complex business today calcaneal fracture calcium scoring canned reports carcinoma esophagus carcinoma stomach cardiac ct/pet cardiac pacemaker cardiogen 82 cardiothoracic imaging catrotid artery dissection cavernoma cervical lymphnode levels chest radiographic score chest radiographs choledocolithiasis classification cloud computing cochlear implant colloid cyst communication in radiology compare case concha bullosa congenital brain anomalies congenital heart disease coronary CT coronary artery disease corpus callosum agenesis craniopharyngioma cryptococcal meningitis ct abdomen and pelvis cystic renal disease dams usmle dams visual treat deep brain stimulator dengue dengue hemorrhagic fever developmental dysplasia devices diagnostic imaging dialysis diffusion MR imaging diffusion tensor imaging diffusion tractography digital radiography distal facial neuroma dsa duplication gall bladder echinococcus echocardiography ectopic kidney elearning elevated diaphragm epilepsy esop facial neuroma fibular osteosarcoma functional mri gastrointenstinal tuberculosis germinoma gifts glioma google google plus gun shot injury haemangioblastoma health 2.0 healthcare consultancy hemangiblastoma hemophilia hippocampus hirayama disease hydatid cyst hypercoagulable hypoxic ischemic encephalopathy indian conferences inferior rectus anomaly infrared interior tomography interstitial lung disease intramedullary metastates intramedullary tuberculomas ipad ipad 2 jacoud's arthropathy kernohan's notch knee kohler's disease krukenberg tumour laceration leber's optic atrophy liver transplant lung contusion lymphatics macros marchifava bingami disease mastoiditis maxillary sinus mucocele medial malleolus ossicle medial tibial stress syndrome medical writting medicare medicolegal aspects of teleradiology migraine mortality motor area mri knee mri lumbal msk penang course mucinous cystadenoma multicentric Glioblastoma multiforme mycotic pseudoaneurysm of superficial temporal artery nephrogenic systemic fibrosis nephrology neurosurgery meets nonradiologist oesophagus olecranon spur online medical games open access opercular syndrome opinion orbit os odontoideum os radiale externum osirix osteochondritis osteochondroma osteoid osteoma outsourcing radiology ovarian tumour parameniscal cyst paranasal sinuses parotid vascular mass patellar sleeve avulsion fracture patent ductus arteriosus patent foramen ovale patient information pelvic MRI pericardial fat phaeochromocytoma pharmaceutical writting pineal tumour placenta accreta placenta increta placental insufficiency pneumococcal pneumonia polycystic kidney disease portal Hypertension posterior circulation stroke power point presentation primary complex protected health information pseudobulbar palsy pseudomyxoma peritonei publications pulmonary edema pulmonary embolism pulmonary tuberculosis rabbit ear sign rad radiographic deterioration pattern radiography radiolo radiologist blogs radiology city radiology debate radiology images of spleen radiology intervensional radiology learning radiology search engine radiology spotter radiology spotters radiolopolis raditudes rathke cleft cyst renal imaging renal sinus tumour right sided aortic arch robot round cell tumour sacral agenesis scaphoid fracture schatzki ring scientific content screening search engine secondaries secondary ossification centres silicosis social radiology soft tissue chondroma solitary pulmonary nodule spectroscopy spinal arachnoid cyst spinal cord tumours spinal osteochondroma spine tumour spinoglenoid cyst sternal tuberculosis stress fracture sacrum stroke mri sub-acute combined degeneration subclavian pseudoaneurysm subependymal giant cell astrocytoma sumer sethi swyer-james syndrome syringomyelia tb teaching video teleradiolo teleradiology business models teleradproviders teleultrasound temporal bone fracture tendoachilles testicular tumour tethered cord. MRI tibial stress fracture total knee arthroplasty total shoulder replacment trachea. tracheal diverticulum tracheal stenosis tracheomalacia traumatic lung cyst triceps tear triquetral fracture tubercular abscess tuberculoma tuberculosis elbow ultrasound image of The segments of the liver umblical artery doppler uroradiology vascular malformation vasovist venous angioma ventriculitis video ct scan video mri viral encephalitis vitamin deficiency