Articles

Articles are a collaborative effort to provide a single canonical page on all topics relevant to the practice of radiology. As such, articles are written and edited by countless contributing members over a period of time. A global group of dedicated editors oversee accuracy, consulting with expert advisers, and constantly reviewing additions.

25 results found
Article

T1 relaxation time

The T1 relaxation time, also known as the spin-lattice relaxation time, is a measure of how quickly the net magnetisation vector (NMV) recovers to its ground state in the direction of B0. The return of excited nuclei from the high energy state to the low energy or ground state is associated with...
Article

T1 rho

T1 rho, also referred to as T1ρ or "spin lock", is an MRI sequence that is being developed for use in musculoskeletal imaging. At the moment it is mostly investigational and does not yet have widespread clinical use. The "rho" in the sequence name refers to a "ro"t...
Article

T1 weighted image

T1 weighted image (also referred to as T1WI or "spin-lattice" relaxation time) is one of the basic pulse sequences in MRI and demonstrates differences in the T1 relaxation times of tissues. A T1WI relies upon the longitudinal relaxation of a tissue's net magnetisation vector (NMV). Ba...
Article

T2 relaxation

T2 relaxation refers to the progressive dephasing of spinning dipoles following the 90° pulse as seen in a spin-echo sequence due to tissue-particular characteristics, primarily those that affect the rate of movement of protons, most of which are found in water molecules. This is alternatively k...
Article

T2 shine through

T2 shine-through refers to high signal on DWI images that is not due to restricted diffusion, but rather to high T2 signal which 'shines through' to the DWI image. T2 shine through occurs because of long T2 decay time in some normal tissue. This is most often seen with subacute infarctions due ...
Article

T2 washout

T2 washout is a phenomenon encountered on diffusion weighted imaging (DWI) which results in DWI images (e.g. B = 1000) appearing normal despite abnormal ADC maps.  For the phenomenon to occur a particular combination of ADC and T2 signal intensity is required.  increased T2 signal facilitated...
Article

T2 weighted image

T2 weighted image (T2WI) is one of the basic pulse sequences in MRI. The sequence weighting highlights differences in the T2 relaxation time of tissues. Summary TR: long TE: long flip angle: less important than with T1 weighting fat: intermediate-bright fluid: bright Physics A T2WI relie...
Article

T2* relaxation

T2* decay refers to an exponential decrease in Mxy  (i.e. signal strength) following the initial excitation pulse as a function of time constant T2*. A picture of the signal or free induction decay (FID) is shown on the right, occurring immediately after a 90o RF excitation pulse in a liquid pha...
Article

Tc-99m HMPAO labelled WBC

Tc-99m HMPAO (hexamethylpropyleneamine oxime) labelled WBC is one of the technetium radiopharmaceuticals used in WBC imaging. Characteristics photon energy: 140 KeV physical half life: 6 hours biological half life: 4 hours normal distribution: spleen, liver, kidney, bone m...
Article

Tc-99m labeled RBC

Tc-99m labelled RBC is one of the technetium radiopharmaceuticals used in renal imaging. Characteristics photon energy: 140 KeV physical half life: 6 hours biological half life:  normal distribution: heart, vessels, spleen miscellaneous facts: threshold for detecti...
Article

Tc-99m MAG3

Tc-99m MAG3 (mercaptoacetyltriglycine) is one of the technetium radiopharmaceuticals used in renal imaging. Characteristics photon energy: 140 KeV physical half life: 6 hours biological half life: 4 hours normal distribution: kidneys (100%) pharmacokinetics: uptake by tubular secretion (9...
Article

Tc-99m Sulfur colloid

Technetium-99m sulfur colloid is one of the technetium radiopharmaceuticals.  Characteristics photon energy: 140 keV physical half life: 6 hours biological half life normal distribution:  liver: 85% spleen: 10% bone marrow: 5% excretion: hepatic target organ: liver, spleen pharmacokin...
Article

Temporal resolution

Temporal resolution relates to the duration of time for acquisition of a single frame of a dynamic process, i.e., cine imaging. Discussion The concept of temporal resolution is fundamental to cardiac CT and MRI, in which a rapidly beating heart is imaged over the order of milliseconds into mul...
Article

Thallium 201 chloride

Thallium 201 Chloride is a radiopharmaceutical used in cardiac imaging. Characteristics photon energy: 80 keV physical half life: 55 hours biological half life rest: 3 minutes exercise: 30 seconds normal distribution: myocardium, skeletal muscle, GI tract, liver, kidneys excretion: renal...
Article

Thermal index

The thermal index (TI) is intended as a measure of an ultrasound beam's thermal bioeffects. It is often displayed on ultrasound screens (along with the mechanical index). Absorption of sound waves may cause heating in tissue. The thermal index depends on: a measure of time-averaged acoustic po...
Article

Thermionic emission

Thermionic emission is the emission of electrons from a heated metal (cathode). This principle was first used in the Coolidge's tube and then later in the modern day X-ray tubes. Before the discovery of the principle, gas tubes were used for X-ray production. The cathode has its filament circui...
Article

Thermoluminescent dosimeter

Thermoluminescent dosimeter (TLD) is a passive radiation detection device that is used for personal dose monitoring. It is based on CaSO4:Dy discs in teflon matrix. Parts plastic holder nickel-coated aluminium card with TLD discs the discs are made of a thermoluminescent material (CaSO4) dop...
Article

Thyroid scan (Tc-99m)

Tc-99m [pertechnetate] thyroid scan is one of the functional nuclear medicine studies that can be used to assess the thyroid gland. patient preparation NPO for 4 hours prior to exam radiopharmaceutical Tc-99m pertechnetate dose and route of administration 3-5 mCi IV time of imaging 20 mi...
Article

Time gain compensation

A way to overcome ultrasound attenuation is time gain compensation (TGC), in which signal gain is increased as time passes from the emitted wave pulse. This correction makes equally echogenic tissues look the same even if they are located in different depths. The basis of this is that of return...
Article

Time of flight angiography

Time of flight angiography (TOF) is an MRI technique to visualize flow within vessels, without the need to administer contrast. It  is based on the phenomenon of flow-related enhancement of spins entering into an imaging slice. As a result of being unsaturated, these spins give more signal that ...
Article

Tissue weighting factor

The tissue weighting factor (WT) is a relative measure of the risk of stochastic effects that might result from irradiation of that specific tissue. It accounts for the variable radiosensitivities of organs and tissues in the body to ionising radiation. To calculate the effective dose, the indi...
Article

Tube arcing

Tube arcing occurs when there is a short-circuit within the tube, typically from the cathode to tube envelope. This causes a momentary loss of x-ray output. New tubes are more prone to this problem due to residual gas within them.
Article

Tumour specific MRI contrast agents

Tumor specific MRI contrast agents are pharmaceuticals that are targeted to tumors, either specifically or nonspecifically. Monoclonal antibodies are targeted to specific tumors such as adenocarcinoma of the colon. Metalloporphyrins exhibit affinity for many tumor types including carcinoma, sarc...
Article

Turbo Inversion Recovery Magnitude

A TIRM or Turbo inversion recovery magnitude sequence is type of  inversion recovery MRI pulse sequence. It has be shown to be superior in the asseesment of osteomyelitis in bone 1 and in the asessment of head and neck tumours 2.
Article

Twinkle artefact

Twinkle artefact is the result of intrinsic machine noise seen with colour Doppler ultrasound 1. It occurs as a focus of alternating colours on Doppler signal behind a reflective object (such as calculi), which gives the appearance of turbulent blood flow 2. And it appears with or without an ass...

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