Biologic Effects

Download Biologic Effects

Post on 24-Feb-2016

30 views

Category:

Documents

0 download

Embed Size (px)

DESCRIPTION

Biologic Effects. Biological Interactions. Radiation Ultrasound MRI. Biological Effects of X-rays. Mutagenic Teratogenic Life shortening Lethal Carcinogenic. ELECTROMAGNETIC SPECTRUM. MRIRadar X-Rays. V i s i b l e. Infra-Red. Television. Cosmic Ray Photons. A-M Broadcast. - PowerPoint PPT Presentation

TRANSCRIPT

Biologic Effects

Biologic Effects

In this segment we will be discussing the various biological effects of commonly used imaging modalities.1Biological InteractionsRadiationUltrasoundMRI

2We will be talking about the biological interaction of radiation, ultrasound, and MRI with soft tissues and other structures.

Biological Effects of X-raysMutagenicTeratogenicLife shorteningLethalCarcinogenic

3The first thing Id like to speak about is the biological effects of x-ray. X-ray could have mutagenic effect causing genetic mutations. It may have a teratogenic effect. It may lead ultimately to a shortening of life, and potentially significant exposure to x-ray can be lethal and lead to death. Both mutagenic, teratogenic effects can lead to carcinogenesis, so carcinoma can be a complication of the biologic exposure of radiation.

ELECTROMAGNETIC SPECTRUMMRIRadar X-RaysPhoton Energy (eV) +810VisibleInfra-RedF-MBroadcastTelevisionCosmic RayPhotonsA-MBroadcastUltra Violet -810 -610 -410 -210 -010 +210 +410 +610

4As we look at this chart of electromagnetic spectrum, we note that x-rays falls to the right hand side of his chart in areas of higher energy. Also included in this area would be gamma rays utilized in nuclear medicine, and the breakdown products of positron emissions as evaluated and seen in PET scanning. Note that MRI falls to the left-hand side of this table, related to the use of radio frequencies in MRI imaging.

Mechanism of Biological Effects of X-raysPhotonBundle of energyPhotons with > 15 ev of energy can ionize an atomIonizationEjection of one or more orbital e- by a photonCreates ion pair: dislodged e- and ionized atomIons are unstable and give rise to free radicals

5The biological effects of x-ray is related to the mechanism that includes the x-ray photon, which is a bundle of energy. Any photon with more than 15 electron volts of energy can, in an interaction with an atom, lead to ionization of that atom. This ionization leading to ejection of one or more of the orbital electrons by that photon, ultimately, resulting in the creation of an ion pair, a dislodged electron in an atom that is ionized, that has a positive charge. These ions are unstable and ultimately give rise to the production of free radicals.

H2OH2O+ e-OH- + H++OH- + H+H20orH + H H2OH- + OH-H202H+ = free hydrogen RadicalOH- = free hydroxy radicalH2O2 = hydrogen peroxideX-ray PhotonFree Radical Production

6Free radical production, as demonstrated in this short slide, is caused by the interaction of that x-ray photon with the water molecule. The water molecule dissociates into a positively charged water molecule in a free electron. That water molecule may disassociate into OH- (hydroxyl) ions as well as H+(hydrogen) ions. If the hydroxy ion and the hydrogen ions re-combine into water, there is no free radical formation. However, a percentage of these free ions will reconfigure in a different arrangement, the hydrogen ions may interact with each other, creating H2 or hydrogen gas. The hydroxide ions may reconstitute themselves into H2O2 or peroxide which will be a problem for the cell.

Free RadicalsAtom or group of atoms with an orbit containing a single unpaired e-Produced by ionization or excitationExtra e- can be transferred from molecule to molecule Free Radical.Free Radicals create critical changes in organic molecules RADIATION DAMAGE affect cell structure and function

7Free radicals simply refer to an atom or group of atoms within orbit that contains a single un-paired electron. These are typically produced by ionization or excitation as occurs when an x-ray photon or gamma ray photon interacts with tissue. This extra electron can be transferred from a molecule to another molecule with the creation of a free radical. The free radicals create critical changes in organic molecules, which we refer to as radiation damage. This interaction can lead to changes in cell structure and ultimately can lead to changes in cell function.

Risk Benefit RatioEvaluate value of the risk to radiation exposure to see if it is outweighed by the benefit that the patient, or society receives as a result of the exposure For example, small risk of future cancer as a result of radiation therapy, large current benefit if treatment causes cure or remission of a fatal disease

8When we review the impact of radiation on patients and possibility of causing damage with x-radiation or gamma radiation thats used in the diagnostic nature, it's important that we do an evaluation of the risk-benefit ratio. We evaluate the value of the risk of the radiation exposure to see if it may be outweighed by the ultimate benefit to that patient or, if not to that individual patient, the benefit that society may experience as a result of exposing that particular individual. For example, a small risk of inducing a future cancer as a result of radiation therapy is balanced against a very large current benefit if the treatment causes a cure or remission of the fatal disease.

Risk Benefit RatioDiagnostic imaging involves relatively low levels of exposureDiagnostic information exceeds the risk of injury to the patient

9Diagnostic imaging typically involves relatively low levels of exposure. This has been complicated in recent years by the introduction of CT scanning and multi-slice CT scanning, well talk a little bit more about that as we talk about the risks of x-ray exposure. Typically the diagnostic information exceeds the risk of injury to that individual patient or to the population as a whole.

Lowest Exposures PossibleFewest exposures necessaryModern equipmentOnly request necessary procedures

10The goal in diagnostic imaging is to achieve the lowest exposures possible. The fewest exposures necessary to provide adequate diagnostic information, using modern equipment, and having our referring physicians only request procedures that are necessary and will impact the ultimate care of a patient.

Image Gently Campaignwww.imagegently.orgAction group to reduce radiation exposure especially to childrenResources including brochures and table for parents record keeping

In an attempt to reduce the overall exposure to individuals, especially to children, a campaign called The Image Gently campaign has been established and has been subscribed to by most radiologists and radiology practices, as well as hospital radiology departments. You can access their site at www.imagegently.org. This action group hopes to reduce radiation exposure, especially exposures to children. At their site, there are resources available including brochures and tables that might be used by parents to keep a record of radiation exposure to their children. A similar record could be kept for adults as well.

11US Per Capita Effective Medical Radiation DoseRecent literature Frequency of exams increased 10 fold from 1950Exposure increase 6 fold from 1980Increase from 0.5 mSv 1980 to 3.0 mSv 2006Majority of exposure increase related to CT scanningRadiology November 2009 Vol. 253 No. 2 pp 520 - 531

Recently, reported as recently as November 2009 in the radiology literature the particular journal being Radiology, there has been an increase in United States of the per capita effective medical radiation dose. Review of this literature indicates that the frequency of examinations using ionizing radiation has increased tenfold when compared to 1950. This, in a large part related to the introduction of new technologies including CT scanning and PET scanning. The exposure increase, however, has rapidly increased in the last 20 years with a sixfold increase noted since 1980. There has been an increase from 0.5 mSv in 1980 to 3 mSv in 2006. And again, the majority of this exposure increase is related to the introduction of multislice CT scanning.

12X-RayStandard imaging relatively low exposuresFluoroscopy moderate to high exposuresCT Scanning moderate to high exposures

13X-ray in standard imaging techniques results in relatively low exposures to patients. Relatively few in number, and relatively low exposure per individual exposure. Fluoroscopy, on the other hand, a mechanism for obtaining motion picture or wide evaluation using x-ray exposure, provides moderate to high exposures, dependent upon the amount of time the x-ray tube remains on. This can become problematic, especially in interventional procedures, or procedures such as coronary catheterization. CT scanning introduces moderate to high exposures the patients, related to the density of the scanning, the number of slices are obtained, and the ease of which multiple sets of exposures can be obtained following various manipulations.

Radiation measurements and equivalentsEffective dose = mSvRisk equivalence 1 mSvSmoking 75 cigarettes1 glass wine/ day 6months125 miles by motorcycle2500 miles by carRock climbing 75 minutesCanoeing 5 hoursUCSD Human Research Protection Program

14In talking about radiation safety and radiation biology, we use radiation measurements and equivalents to provide some perspective on the tightened amount exposure. An effective dose is called a mSv. Its a measurement of radiation and its impact upon biologic tissues. Risk equivalents are related to one mSv of exposure or dose. This is equivalent to smoking 75 cigarettes, drinking a glass of wine per day for 6 months, taking a 125-mile ride by motorcycle, or driving 2500 miles in the car. If you like to rock climb over in Graham Ledge, 75 minutes of rock climbing has the same risk equivalents of one mSv of radiation exposure. Similarly, if you like canoeing down the Grand River or the Red Cedar River, 5 hours of canoeing would result in the same risk. This based on statistic