longitudinal relaxation time


longitudinal relaxation time

An MRI term for the time constant, T1, that defines the rate at which excited protons return to equilibrium within the lattice, which reflects the time required for spinning protons to re-align themselves with the external magnetic field. Post excitation magnetisation increases from 0% to ±63% of its final value in time T1.

time

(tim) The interval between beginning and ending; measured duration.

activated partial thromboplastin time

Abbreviation: APTT
A laboratory test to measure the intrinsic pathway of coagulation. In health, the APTT is about 16 to 40 sec, depending on the laboratory methods used. Prolonged PTT may indicate cirrhosis of the liver, disseminated intravascular coagulation, blood clotting factor deficiencies (VIII, IX, X), decreased levels of fibrinogen in the blood, von Willebrand's disease, or the presence of a lupus anticoagulant.

arise time

In sleep medicine, the time when a person gets out of bed after sleeping as opposed to the time a person becomes alert and awake after sleep.

association time

See: association test

backup time

In radiography, the time setting selected before an automated exposure, usually 150% of the anticipated total exposure time for projection.

bleeding time

The time required for blood to stop flowing from a small wound or pinprick. It is assessed using one of several techniques. Depending on the method used, the time may vary from 1 to 3 min (Duke method) or from 1 to 9 min (Ivy method). The Duke method consists of timing the cessation of bleeding after the earlobe has received a standardized puncture. The Ivy method is done in a similar manner following puncture of the skin of the forearm. The validity of this test to predict clinically significant bleeding has been questioned.

bowel transit time

The length of time it takes for food (or a marker dye) to pass through the gastrointestinal tract, from ingestion to defecation. It is shorter in conditions such as malabsorption and more prolonged in constipation.

circulation time

The time required for a drop of blood to make the complete circuit of both the systemic and pulmonary systems. Circulation time is determined by injecting a substance into a vein and timing its reappearance in arteries at the injection point. The blood with the contained substance must pass through veins to the heart and through the right atrium and ventricle, through the pulmonary circuit to the lungs, and back through the left atrium and ventricle, and then out through the aorta and arteries to the place of detection. Dyes such as fluorescein and methylene blue and substances such as potassium ferrocyanide and histamine have been used as tracers. Average circulation time is about 1 min.

Circulation time is reduced in anemia and hyperthyroidism and is increased in hypertension, myxedema, and cardiac failure. Circulation time may also be measured by injecting into a vein a substance that can be tasted when it is transported to the tongue. The normal circulation time from an arm vein to the tongue is 10 to 16 sec. In the aorta, the blood flows at a speed of approx. 30 cm/sec.

clot retraction time

The time required following withdrawal of blood for a clot to completely contract and express the serum entrapped within the fibrin net. The normal time is about 1 hr. Clot retraction depends on the number of platelets in the specimen.

coagulation time

The time required for a small amount of phlebotomized blood to clot. This can be determined by collecting blood in a small test tube and noting elapsed time from the moment blood is shed to the time it coagulates.

cold ischemia time

Abbreviation: CIT
The time that an organ surgically removed for transplantation remains in a chilled perfusion solution before engraftment.

cycle time

The period between regular events, e.g., inflations of an automated blood pressure monitor.

doubling time

The length of time needed for a malignant tumor cell population to double in size.

door-to-balloon time

The delay between the arrival at a hospital of a patient with an acute myocardial infarction and the opening of the patient's obstructed vessel by percutaneous coronary intervention. The delay should be 90 min or less for optimal outcomes.

dwell time

The length of time a therapeutic substance will be retained in the body.

euglobulin lysis time

A test that determines how rapidly blood clots dissolve. It is used to identify diseases such as disseminated intravascular coagulation, and to monitor the effect of thrombolytic drugs, such as streptokinase and the recombinant enzyme tissue plasminogen activator.

forced expiratory time

Abbreviation: FET
The time required to forcibly exhale a specified volume of air from the lung.

gestation time

The duration of a normal pregnancy for a species. See: pregnancy for table

intestinal transit time

The speed with which consumed food passes through the gut. It is slowed by anticholinergic agents (such as tricyclic antidepressants) and by neuropathic diseases of the stomach or intestines, e.g., diabetes mellitus. Many agents increase intestinal transit, including erythromycin and nonabsorbable laxatives.

into-bed time

In sleep medicine, the time when a person lies down for his or her major sleep time of the day as opposed to other periods of sleep.

kaolin cephalin time

Abbreviation: KCT, KCCT
A laboratory test to measure the health of the intrinsic pathway of coagulation (the function of clotting factors VII, IX, XI, and XII). When a prolonged kaolin cephalin clotting time does not normalize after the addition of normal plasma, a lupus anticoagulant is present in the blood.

longitudinal relaxation time

T1 time.

lost time

In occupational health, the number of hours, days, or weeks that an employee does not appear for work, as a result of illness, injury, absenteeism, workers' compensation, or unpaid leave.

median lethal time

The time required for half of a population to die after exposure to ionizing radiation.

partial thromboplastin time

The time needed for plasma to clot after the addition of partial thromboplastin. It is used to test for defects of the clotting system.

prothrombin time

Abbreviation: PT
The time it takes for clotting to occur after thromboplastin and calcium are added to decalcified plasma. The test is used to assess levels of anticoagulation in patients taking warfarin, to determine the cause of unexplained bleeding (as in patients with hemophilia), or to assess the ability of the liver to synthesize blood-clotting proteins. See: international normalized ratio

quiet time

1. The time between measurable events, e.g., in respiratory care, the time between inspiration and expiration.2. A time of silent reflection, thought, or prayer.

reaction time

The period between application of a stimulus and the response.

real time

Moment-to-moment or second-to-second dynamic. It is used, e.g., of imaging technologies that take moving pictures rather than static images of body structures.

recovery time

1. The time between the end of an anesthetic infusion and the opening of a patient's eyes.2. The time between the end of an anesthetic infusion and the patient's ability to oxygenate and ventilate without mechanical assistance.

reptilase time

Abbreviation: RT
A test to identify hypofibrinogenemia or dysfibrinogenemia in plasma.

response time

1. The delay between the first administration of a medication and the onset of or recovery from its effects.2. The duration of a reaction.

saturation time

The time required for the arterial blood of a person inhaling pure oxygen to become saturated.

screen time

The number of hours that a person spends each day in front of a computer, or watching movies or television, or playing video games.

setting time

The time required for a material to polymerize or harden, as in dental amalgam, cement, plaster, resin, or stone.

spin lattice relaxation time

T1 time.

spin-spin relaxation time

T2 time.

T1 time

The time it takes for a proton that has been stimulated by radiofrequency (RF) energy to relax back into its usual alignment in tissue. Each tissue in the body has its own distinguishing relaxation time and its own distinctive energy emission after stimulation with RF energy. These physical characteristics of tissues are exploited in magnetic resonance imaging to create pictures of body structures. Synonym: longitudinal relaxation time; spin lattice relaxation time

T2 time

The time it takes for neighboring, radiofrequency-stimulated protons to relax relative to other protons in tissue (rather than relative to the magnetization provided by a magnetic resonance imaging (MRI) device). The T2 time varies from tissue to tissue. This is exploited in MRI to help generate contrast between adjacent tissues, e.g., between the white matter and grey matter of the brain, or between tissues with high fat content as opposed to those with high water content. Synonym: spin-spin relaxation time; transverse relaxation time

taipan snake venom time

A test to determine the presence of lupus anticoagulant in a blood specimen. The test relies on the mixing of venom from snakes of the genus Oxyuranus with dilute phospholipid and can be used even in patients receiving warfarin anticoagulation.

template bleeding time

A bedside test to determine the presence of abnormal delays in blood clotting, in which a small cut is made in the skin, and the time it takes for bleeding to stop is measured.

time in the therapeutic range

Abbreviation: TTR
An estimate of the average time that a medication is dosed with optimal efficacy and safety. The term is usually used with respect to anticoagulants such as warfarin but can apply to any agent whose drug levels are monitored.

thermal death time

The time required to kill a bacterium at a certain temperature.

transverse relaxation time

T2 time.

turn-around time

, turnaround time Abbreviation: TAT
The time it takes to process an order, carry it out, and report the results, e.g., the time between ordering and reporting laboratory test results.

Patient care

In the rushed environment of contemporary hospitals, especially in emergency departments and intensive care units, TAT can be a problem between physicians and nurses who order lab tests and the laboratorians who complete them and report the results. At the bedside, TAT starts with the ordering of the test. In the lab it begins when the specimen or the order for the test is received; next it is processed; and, finally, the results are reported to the clinician. Decreasing TAT without sacrificing the quality of reported results makes timely modifications in treatment possible; it requires careful planning at the bedside, a rapid system of specimen transport, an easy-to-use order entry system and log, and an efficient laboratory with well-trained professional staff.