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What kind of procedures require informed consent from patients?
what must be clearly explained in a language the patient fully comprehends about an invasive procedure that makes a consent "informed"
explanation of the procedure, its risks, benefits, and alternatives
patient's questions before an invasive procedure must be answered by whom?
by qualified personnel before the procedure is begun
Who can sign a form documenting informed consent for an invasive procedure?
- the patient or a competent, legal representative
- a parent or legal guardian for minors
What is implied consent?
- when a patient is in need of immediate medical services but is unconscious or is physically unable to consent to treatment
- in this case, services are rendered with the assumption that the patient would consent if able
what is the key to any successful patient interaction?
when does patient screening and education begin to identify concerns regarding exam tolerance, potential contrast agent contraindications, and so on?
during scheduling/screening process
before contrast agent administration, what must be discussed with the patient to prevent any surprises during the scan?
potential physical effects, such as warm sensation and metallic taste
what consists of a complete patient history documentation?
patient's recent procedures, surgeries, symptoms, possibe trauma, and specific areas of pain or discomfort
What is assessed when monitoring a patient's condition?
vital signs which consists of temperature, pulse, blood pressure, and respirations.
what is a normal body temperature?
- 97.7 to 99.5 degrees F or
- 36.5 to 37.5 degrees C
what are the normal pulse rates for adults and children?
- 60-100 beats/minute for adults
- 70-120 beats/minute for children
what is a normal blood pressure?
- systolic which indicates the pressure within arteries during cardiac contraction should be less than 120mm Hg
- diastolic is measured during relaxation of the heart and should be less than 80mm Hg
what is a normal respiration rate for adults and children?
- 12-20 breaths/minute for adults
- 20-30 breaths/minute for children
what is a pulse oximeter and what does it measure?
- an electronic device used to measure pulse and respiratory status.
- placed on a patient's finger, toe, or ear lobe
- measures blood oxygen levels, which are normally between 95% and 100%
what is an electrocardiogram and for which CT exam is it useful for?
- ECG or EKG is a graphic representation of the electrical activity of the heart
- it is used particularly during cardiac CT procedures to evaluate the heart rhythm and cycle
what is BUN and what are the normal levels?
- BUN- blood urea nitrogen
- 7-25 mg/dL for adults
- is not a sufficient indicator of renal insufficiency by itself
Normal creatinine levels range from what?
what is a normal BUN/creatinine ratio?
what is GFR and what is the normal rate?
- Glomerular filtration rate which is a more accurate measure of renal function. GFR is an approximation of creatinine clearance or the rate by which creatinine is filtered from the blood stream.
- GFR is calculated using the pt's creat level and takes into account the pt's age, sex, and race.
- the normal range for men is 70+- 14 and 60+- for women
what is prothrombin time (PT) and what is the normal range?
- is a measure of blood coagulation
- the normal range for PT is around 12-15 secs
what is partial thromboplastin time (PTT) and what is the normal range?
- used to detect abnormalities in blood clotting
- normal range for clotting time is generally 25-35 secs
what is platelet count and the normal range?
- used to assess the patient's clotting ability.
- normal platelet count is 140,000 to 440,000
what is coumadin and what precaution should the CT tech take if a pt is taking it?
- is a proprietary name for the generic drug warfarin, an anticoagulant. It prevents blood from clotting in veins and arteries
- reduces incidence of heart attack and stroke
- adequate pressure must be applied to the site after IV removal to avoid excessive bleeding and bruising
what is metformin and why could it be harmful for pt's after IV contrast administration?
- is a drug, also commonly referred to by the brand name Glucophage, is a drug used to treat type 2 diabetes.
- pts are typically instructed not to take a metformin product for up to 2 days following contrast-enhanced CT exam because there is a small risk of renal impairment from iodinated contrast agents, and reduced renal function can cause the potentially harmful retention of metformin within the body
what is venipunture?
- is the process of obtaining intravenous access for the purpose of intravenous therapy or for blood sampling of venous blood.
- the injection of a medication or contrast agent directly into the bloodstream is a type of parenteral adminstration
what are the common sites used for IV administration of contrast?
- anterior recess of the elbow or antecubital space
- radial aspect of the wrist
- anterior surface of the forearm
- posterior portion of the hand
what is aseptic technique?
- it refers to the practices and procedures that a practitioner employs to reduce the risk of infection during the IV administration of contrast media
- thorough hand washing between pts
- wearing of disposable gloves
- cleaning of the site of venipuncture in a circular motion with an alcohol swab, moving from the center to the outside
- application of gentle pressure with an alcohol swab to the venipuncture site after removal of the needle/catheter
what is sterile technique?
- refers to the practices and procedures used to maintain a sterile, microorganism-free environment during invasive CT procedures such as biopsy, aspiration, and CT arthrogram
- involves establishing a field around the area of interest that is free of all microorganisms. the procedure is performed within this sterile field with the use of sterile equipment and supplies
what are two approaches to IV adminstration of iodinated contrast agents?
- drip infusion- whereby the volume of contrast agent is administered at a slow rate over a long period. this is no longer used because this method results in a slow rise in blood iodine concentration
- Bolus injection- whereby the IV contrast agent is "pushed" into the bloodstream at a rapid rate over a short period. this results in a sharp peak of iodine concentration in the blood, yielding a more pronounced pattern of contrast enhancement
IV administration of contrast agent by power injector should be performed through what kind of catheters?
flexible plastic angiocatheters rather than standard metal needles
22-gauge and 20-gauge angiocatheters are sufficient for flow rates up to what amount?
- 22-gauge- up to 3mL/sec
- 20-gauge- greater than 3mL/sec
what are the advantages of automatic power injectors over hand injecting IV contrast?
- consistent, reproducible flow rates
- precise volume/dosage control
- higher injection rates for optimal contrast enhancement
- automatic delays for proper enhancement patterns and multiphase imaging
what is the advantage of administering normal saline as a flushing agent by an automatic injector right after injection of IV contrast?
reduces streaking and reduces contrast agent dose
what is the major disadvantage of using a power injector?
the increased risk of extravasation, or infiltration of the contrast agent outside the blood vessel
what are the two main basic types of contrast agents utilized during CT procedures?
- positive- iodine and barium
- negative- air, gases, water
- neutral- used to visualized the small bowel during CT enterocylsis and CT enterography. very low-density barium sulfate solutions such as VoLumen may be used for the small bowel
what are the two categories of iodinated radiopaque contrast media (RCM)?
- Ionic contrast media- conray and hypaque
- Non-ionic contrast media- omnipaque, isovue, optiray. Non ionic iso-osmolar (visipaque)
- non-ionic low-osmolar contrast agents are less likely to produce adverse side effects and/or reactions than ionic high-osmolar RCM
what is an enteral Radiopaque contrast media(RCM)?
- either a water-soluble iodinated solution or a suspension of barium sulfate
- can be used as oral and rectal contrast for opacification of the GI tract
- routine transit time through the GI tract is typically 30-90 mins
what are the contraindications for using barium sulfate oral contrast and for water-soluble oral contrast?
- Barium sulfate- suspected perforation of the GI because it may be toxic to the peritoneum
- pts who are to undergo surgery or other invasive procedures of the abdomen/pelvis
- harmful if aspirated
- Water-soluble oral contrast- iodine allergy
what is intrathecal administration and which CT exam is it done for?
- injection directly into the space surrounding the spinal cord
- done for CT myelography for evaluation of the spinal cord and nerve roots
what is intra-articular administration and which CT exam is it done for?
- injection directly into a joint space
- done for CT arthrography of joints including the shoulder, wrist, and knee
what are the 4 Hs as outlined by the American College of Radiology (ACR) in regards to pts undergoing administration of iodinated contrast agents?
- history- obtain thorough pt history, allergies
- hydration- pts with compromised kidneys must be hydrated before, during, and after the exam
- have equipment and expertise ready- a detailed plan to treat contrast agent reactions should be in place and should be practice regularly
- heads up- constant assessment of the patient's condition is vital for early identification and proper treatment of an adverse reaction
what medications can you give a pt that has increased risk of adverse reaction to iodinated contrast before a CT exam with IV contrast?
can be a combination of antihistamine such as diphenhydramine HCL (benadryl) and a corticosteroid taken at timed intervals beginning as early as 24 hours before contrast agent injection
what are the contraindications to IV iodinated contrast agents?
- allergy to iodine
- prior severe allergic reaction to an iodinated contrast agent
- renal insufficiency/failure
what are the instructions for nursing mothers who undergo IV contrast studies to eliminate risk of excreting iodinated contrast in their breast milk?
to pump and discard breast milk for 24 hours after administration of a contrast agent
what are considered as mild reactions to IV contrast?
- mild urticaria (hives)
- pronounced sensation of warmth and or flushing
- altered taste
- nasal stuffiness/sneezing
- requires no treatment but must be closely observed until symptoms dissipate
what are considered moderate reactions to IV contrast?
- mild bronchospasm
- moderate to severe urticaria
- vasovagal response
- tachycardia from hypotension
- usually non life threatening but may progress rapidly, so treatment may be necessary
what are considered severe reactions to IV contrast?
- profound hypotension
- laryngeal edema
- severe bronchospasm
- pulmonary edema
- cardiac arrhythmia
- cardiopulmonary arrest
what are common delayed reactions to IV contrast?
- urticaria (hives)
- pruritus (itchiness)
what is contrast-induced nephrotoxicity (CIN)?
- it is a considerable decline in renal function that can occur after a patient receives IV contrast
- increased creatinine level over baseline before IV contrast is recieved
- related to renal vasoconstriction and/or the toxicity of the contrast medium itself
- overall risk of CIN is directly related to the patient's preexisting renal function and hydration level
- risk factors for CIN includes: diabetes, myeloma, advanced age, cardiovascular disease
what are the two factors affecting CT patient radiation dose?
what are the several characteristics that may affect patient dose from individual technical configuration of a CT system?
- source-detector distance- increased dose when closer to the source
- filtration- varies between 6 and 9mm Al. Removes unwanted "low quality" portion of the xray beam that adds to pt dose
- detector efficiency- inherent absorption efficiency (the ability of the detector to capture transmitted xray quanta and produce the appropriate response) and geometric efficiency (the spatial arrangement of detector elements)
what is overranging?
occurs when radiation dose is applied before and after the acquisition volume to ensure sufficient data collection for the interpolation algorithms inherent in spiral CT
What are adaptive filters?
noise reduction algorithms that are employed during the reconstruction process to reduce displayed noise within the CT image. This allows for lower mAs settings during data acquisition
Why can dose be higher with MSCT (multi-slice CT) than a SSCT (single slice CT) system? Name 4 factors
- decrease in the focal spot-detector distance
- use of a cone beam instead of a more z-axis collimated fan beam
- increases in the number of phases of acquisition enabled by decreased scan times
- use of thinner section widths for improvement of three-dimentional and multiplanar reformation (MPR) images
during multidectector CT (MDCT), wider sollimation results in improved or unimproved dose efficiency?
- improved dose efficiency because less overbeaming occurs.
- narrow beam widths, i.e, thin slices, increase overbeaming and reduce dose efficiency
displayed noise on a CT image can be reduced by what kind of technique without increasing pt dose?
the utilization of an appropriate reconstruction algorithm, or kernel and also displaying the reconstructed image with the correct window and level settings
True or False: image noise is directly related to patient size
- As patient size decreases, noise decreases
Pitch values greater than 1 causes increase or decrease in dose?
- decrease in dose because it allows for the acquisition of a scan in a shorter period of time
- image noise thus increases
The modern CT scanner comes equipped with a form of automatic exposure control (AEC) to manage patient dose on the basis of the size, density and overall attenuation of the part being examined. This is called what?
- Automatic tube current modulation (ATCM)
- Has two different kinds:
- Angular (x-and y-axis) tube current modulation- whereby the mA setting is adjusted according to the difference in thickness of the part as the tube rotates. for example, during imaging of the oval torso, mA can be reduced as the beam passes from anterior to posterior. Less attenuation occurs in the AP path than in the lateral path through the patient
- Longitudinal (z-axis) tube current modulation, which allows for the adjustment of the mA setting as the scan proceeds along the z-axis of the patient. Differences in attenuation as the body thickness and tissue density change from the chest to the abdomen, and so on, are met with appropriate adjustments in mA, resulting in an overall reduction in radiation dose.
- CT scanners can have both
how does ECG-triggered tube current modulation work to reduce pt dose during cardiac CT scanning?
- during MSCT cardiac studies, prospective gating can be used to reduce the patient radiation dose.
- ECG-triggered tube current modulation allows for pulses of x-ray energy rather than continuous exposure to be used
- tube current is reduced during the cardiac phase not utilized for image reconstruction
- the potential radiation dose savings gained with ECG-triggered TCM depend on the pt's heart rate. As heart rate increases, the dose savings decrease
what does slice sensitivity profile (SSP) describe?
- may be used to describe the reconstructed CT section
- however, the section of tissue exposed to ionizing radiation, or dose profile, is greater in width than SSP. The accurate calculation of CT patient radiation dose must take this fact into account
What does the term "exposure" mean?
- it is used to describe the ability of x-rays to ionize a volume of air.
- measured in roentgen (R)
What does absorbed dose mean?
- describes the amount of xray energy absorbed in a unit of mass.
- measured in grays (Gy) or rads
- kerma may also be used, air kerma describes the amount of radiation absorbed in a quantity of air
what is effective dose?
- accounts for the type of tissue that the radiation is deposited in. different tissues are assigned weighting factors based on their individual radiosensitivity. effective dose approximates the relative risk from exposure to ionizing radiation
- measured in seiverts (Sv) or rems
what does the CT dose index (CTDI) measure?
- the dose received in a single CT section or slice
- calculated for the central slice in a series that is surrounded by seven slices on each slice
- measured by performing scans of both head and body-sized CT phantoms using specific technical parameters. A thermoluminescence dosimeter (TLD) is placed within each phantom during the scans.
- The exposure measured by the TLD is used to calculate the CTDI for each acquisition
what does CTDIw measure?
- it is an internationally accepted, weighted dose index
- it is calculated by summing two-thirds of the exposure recorded at the periphery of the field with on-third of the centrally recorded dose. This weighting yields a more accurate dose approximation
- it is calculated from measurements made with TLDs positioned at the center and periphery of the phantom to account for the variance in dose distribution
- it is measured utilizing a conventional step-and-shoot mode of axial CT scanning and dose not account for the affects of helical scanning on patient radiation dose
what does CTDIvol measure?
- the radiation dose for each section obtained during a helical scan
- it corresponds to the axially acquired CTDIw divided by the helical pitch. As the pitch increases the dose per section (CTDIvol) decreases
- CTDIw approximates dose along the x and y axes of the acquired CT image. CTDIvol also includes the dose along the z-axis of the scan, it is given in units of milligrays(mGy)
what does multiple scan average dose (MSAD) measure?
- calculates the average cumulative dose to each slice within the center of a scan consisting of multiple slices
- is higher than the dose from an acquisition of a single slice because of the contribution of scatter radiation
- both CTDIvol and MSAD are used to approximate average radiation dose within a scan volume total scan length along the z-axis is not considered. Therefore, neither provides an estimate of the total dose along a given scan volume, DLP does
what does dose length product (DLP) measure?
- is an internationally accepted measure of CT patient dose defined as MSAD x slice width(cm) x # of slices in scan volume where slice equals the pre-pt collimator setting and not the reconstructed slice thickness.
- DLP can also be illustrated as the product of CTDIvol and scan length and is given in units of milligray-centimeters (mGy-cm)
- CTDIvol and DLP do not account for pt size and so overestimates for large pts and underestimates for smaller pts
what is the difference between infiltration and extravasation?
- Infiltration is the inadvertent leakage of a non-vesicant solution from its intended vascular pathway (vein) into the surrounding tissue
- Extravasation is the inadvertent leakage of a vesicant solution from its intended vascular pathway (vein) into the surrounding tissue
- A vesicant refers to any medicine or fluid with the potential to cause blisters, severe tissue injury (skin/tendons/muscle) or necrosis if it escapes from the intended venous pathway