Volume 2 Number 2 Summer 96

Master List Volume 2 Number 2 Summer 1996

IN THIS ISSUE

What's New in UAB Radiology

Helical CT

FAQs

Radiographic Contrast Media Adverse Reactions

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What's New in UAB Radiology

Helical CT

Helical CT
Shows Aortic Dissection

Helical CT has been available in the UAB Department of Radiology and The Kirklin Clinic since 1992 and is thus not really new. However, its importance has been rapidly increasing as our experience grows and new applications are developed.

Helical CT became possible with the development of slip ring contacts between the gantry and the x-ray tube-detector assembly. This allows the tube-detector assembly to rotate continuously without the time-consuming reversal of scan direction required by conventional scanners to "unwind" the electrical cables. Without the delay caused by "unwinding" the cables, images can be acquired in one second or less. Simultaneous scanning and movement of the patient through the scanner occurs, resulting in a spiral or helical x-ray path on the patient's surface and a three-dimensional data set from which the axial images are constructed. The radiologist and technologist adjust x-ray dose, table speed, slice thickness, and slice interval for each examination according to the reason for scanning.

In scanning the abdomen, Helical CT has several advantages over conventional CT. During conventional CT, the patient breathes every one to three slices; this can result in up to several centimeters misregistration of anatomy from slice to slice depending on how deeply the patient breathes for each scan. Helical CT acquires images in a volumetric fashion covering up to 30 slices in a single breath, almost completely eliminating misregistration. The rapid scan times possible with helical CT also minimize artifacts from breathing, bowel, and patient during the image acquisition.

The interval between the reconstructed images can be selected by the radiologist even after the scans are taken. This allows reconstruction of overlapping images which can be helpful in detecting and characterizing small lesions. This also gives smoother, more accurate images in three-dimensional reconstruction.

The rapid scan times of helical CT allow scanning whole body regions several times after bolus injection of intravenous contrast. This is especially useful in imaging the liver and pancreas where some tumors (for example, hepatocellular carcinoma, metastases from breast and kidney cancers, and melanoma) may be more obvious on images obtained during the arterial phases of contrast enhancement.
Arterial phase scanning after bolus contrast injection can also give three-dimensional angiographic images without arterial contrast injection. CT angiograms can be obtained less invasively, less expensively, and more quickly than conventional arteriograms.

Helical CT has revolutionized CT of the abdomen and allows three-dimensional imaging of the vascular system in all parts of the body. Please contact us at any time so that we may help optimize the imaging evaluation of your patients. We welcome your comments and questions.

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FAQs- Frequently Asked Questions

Q: Radiographic Contrast Media Adverse Reactions

Iodinated contrast media is routinely administered for many radiological procedures like CT, IVP or angiography. Due to the higher absorption of x-ray beams by the iodinated contrast, both normal and abnormal structures are better seen. However, because of the risks of adverse reaction to contrast administration in some patients, judicious use of these agents is required.
The following are frequently asked questions about contrast media and contrast reactions.

Q: How frequently do allergic contrast reactions occur?

It is estimated that the overall frequency of adverse reactions is 5 to 10 percent. Most of these are very mild and may consist of only a few hives. However, in one of every 1,000 to 2,000 examinations, a moderate or severe reaction can occur. In a recent meta-analysis of multiple studies, the risk of death from a contrast agent is estimated to be 0.3 to 2.6 per 100,000 uses (comparable in magnitude to the risk of death from receiving a dose of penicillin).

Q: What types of allergic contrast reactions are seen?

Contrast reactions are classified as mild, moderate, or severe. Mild reactions include mild nausea and vomiting, mild urticaria and pruritus, and mild diaphoresis. Moderate reactions would include more severe presentations of the above symptoms, facial and laryngeal edema or mild bronchospasm. Severe reactions may include hypotensive shock, cardiac or respiratory arrest, pulmonary edema, loss of consciousness, convulsions, and severe laryngeal or bronchial spasm.

Q: How are these contrast reactions treated?

All contrast examinations are performed in the presence of a physician, usually a radiologist in our department, that must be ready to initiate treatment of any reaction. [Guidelines for the treatment of these reactions are also posted in all areas in the radiology department.] Most reactions are mild and require no treatment; outpatients are usually observed for 30 minutes for worsening of symptoms. In most cases, these mild symptoms are self-limiting and will resolve within this time with minimal or no treatment. Adverse episodes related to the administration of intravascular contrast media are monitored as part of our ongoing Department Quality Assurance Program.

Q: What can be done if a patient with a history of contrast reaction needs another contrast exam?

This depends on the nature and severity of the prior reaction. If the prior reaction was mild, selection of a low-osmolar contrast agent ("non-ionic") and/or pretreatment with 25-50 mg of diphenhydramine ("Benadryl") prior to the examination may be all that is needed. If the prior reaction was moderate or severe, a radiologist should be consulted to see if there is an alternative diagnostic imaging strategy (e.g. ultrasound or MRI) that avoids iodinated contrast exposure. Of note, gadolinium based MRI contrast agents have a different formulation from iodinated radiographic contrast media, and there is no known cross sensitivity between these two types of contrast.

If a contrast examination is still felt necessary, premedication with corticosteroids should be performed and low osmolar contrast selected. Two accepted protocols for corticosteroid administration in this setting include 50 mg of prednisone p.o. 12,6, and 1 hour prior to the examination, or 32 mg of p.o. solumedrol 12 and 2 hours prior to the exam. Fifty mg of diphenhydramine at bedtime the evening prior and 1 hour prior to the procedure is usually also administered. The equivalent iv dose of solumedrol can be substituted if the patient is unable to tolerate p.o. administration.

Q: Aren't low-osmolar contrast agents safer?

Low osmolality contrast media (LOCM) are associated with less patient discomfort during administration. However, the risk of death from contrast reaction is felt to be mostly unchanged from that of high-osmolality contrast media (HOCM). The risk of very severe reactions is decreased with low-osmolality contrast but the amount of risk reduction in patients not at high risk for a reaction is very low. In the largest study from data on 337,000 Japanese patients who underwent contrast examination, the estimated risk of severe contrast reaction was 0.04 percent in patients receiving HOCM and 0.004 percent in patients receiving LOCM. In a separate report of 109,000 examinations, respective percentages were 0.09 percent and 0.02 percent for HOCM and LOCM. Thus, for the patient with no known risk factors for contrast reaction, HOCM are felt to be relatively safe.

Q: Why are LOCM not used routinely on all contrast examinations?

Low osmolality contrast agents are about 10 times more expensive than high-osmolality agents. At UAB, the cost of a 150 ml bottle of Conray 60, a typical high osmolality agent, used during a routine CT examination is $9.15 whereas the same dose of Optiray 320 is $94.19. This cost to the patient may not be reimbursed by a third party insurer.

At University Hospital and Kirklin Clinic, all outpatients who will undergo a contrast examination are screened by the radiologic technologist for risk factors including prior reaction, history of severe allergy to any medication, active asthma, current severe cardiac disease, history of sickle cell disease or multiple myeloma, and increased risk of aspiratoin. The radiologist then selects the dose and type of contrast media after reviewing this information. By formalizing the protocol for the use of LOCM, we were able to reduce the use of LOCM at UAB from 40 percent of studies to 15 percent of studies, saving approximately $250,000, without any increase in moderate or severe reactions.

Q: Do Low-Osmolality contrast media have a lower incidence of associated nephrotoxicity?

This is controversial. Patients with insulin-dependent diabetes, volume depletion, and baseline renal dysfunction are a higher risk for contrast induced acute tubular necrosis or transient renal dysfunction. A few studies have suggested a slight benefit to use of LOCM in this setting. In our department, patients with a stable creatinine up to 2.5 mg/dl who need a contrast study are usually given LOCM. The benefits of saline infusion during a 12-hour period prior to examination, and limiting the amount of contrast infused, are better documented in the prevention of nephrotoxicity. Contrast administration in patients with rising creatinine or stable creatine greater than 2.5 mg/dl is not recommended. LOCM is also often used in the patients with end-stage renal disease, not because of concerns of nephrotoxicity but due to the possible hemodynamic effects of an osmotic load in these patients that may also commonly have cardiac disease.

For further information and more complete discussion including references, please contact Dr. Lopez at 934-5135 or by e-mail at blopez@uabmc.edu, or Dr. J. Kevin Smith at 934-7978, jksmith@uabmc.edu.

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Visions is published quarterly by the University of Alabama Hospital Department of Radiology. Professor and Chairman: Robert J. Stanley, M.D. Vice-Chairman for Operations and Academic Affairs: Robert E. Koehler, M.D. Vice Chairman for Planning and Administration: Lincoln Berland, M.D. Director of Outpatient Services: Peter Dempsey, M.D. Visions Staff-Managing Editor: Margaret Ard. Editors/Writers: Lincoln Berland, M.D. Kay Hamrick, M.D. Robert Lopez, M.D. UAB Office of Marketing and Media Relations Staff- Editor: Rhonda Gregg. Art Director: Jason Bickell. Please direct questions, comments, and suggestions as follows: Attention Angie French or Lincoln Berland, M.D. FAX: 975-7213 ADDRESS: NHB 623B EMAIL: lberland@uabmc.edu

Q: Radiographic Contrast Media Adverse Reactions	Iodinated contrast media is routinely administered for many radiological procedures like CT, IVP or angiography. Due to the higher absorption of x-ray beams by the iodinated contrast, both normal and abnormal structures are better seen. However, because of the risks of adverse reaction to contrast administration in some patients, judicious use of these agents is required. The following are frequently asked questions about contrast media and contrast reactions.
Q: How frequently do allergic contrast reactions occur?	It is estimated that the overall frequency of adverse reactions is 5 to 10 percent. Most of these are very mild and may consist of only a few hives. However, in one of every 1,000 to 2,000 examinations, a moderate or severe reaction can occur. In a recent meta-analysis of multiple studies, the risk of death from a contrast agent is estimated to be 0.3 to 2.6 per 100,000 uses (comparable in magnitude to the risk of death from receiving a dose of penicillin).
Q: What types of allergic contrast reactions are seen?	Contrast reactions are classified as mild, moderate, or severe. Mild reactions include mild nausea and vomiting, mild urticaria and pruritus, and mild diaphoresis. Moderate reactions would include more severe presentations of the above symptoms, facial and laryngeal edema or mild bronchospasm. Severe reactions may include hypotensive shock, cardiac or respiratory arrest, pulmonary edema, loss of consciousness, convulsions, and severe laryngeal or bronchial spasm.
Q: How are these contrast reactions treated?	All contrast examinations are performed in the presence of a physician, usually a radiologist in our department, that must be ready to initiate treatment of any reaction. [Guidelines for the treatment of these reactions are also posted in all areas in the radiology department.] Most reactions are mild and require no treatment; outpatients are usually observed for 30 minutes for worsening of symptoms. In most cases, these mild symptoms are self-limiting and will resolve within this time with minimal or no treatment. Adverse episodes related to the administration of intravascular contrast media are monitored as part of our ongoing Department Quality Assurance Program.
Q: What can be done if a patient with a history of contrast reaction needs another contrast exam?	This depends on the nature and severity of the prior reaction. If the prior reaction was mild, selection of a low-osmolar contrast agent ("non-ionic") and/or pretreatment with 25-50 mg of diphenhydramine ("Benadryl") prior to the examination may be all that is needed. If the prior reaction was moderate or severe, a radiologist should be consulted to see if there is an alternative diagnostic imaging strategy (e.g. ultrasound or MRI) that avoids iodinated contrast exposure. Of note, gadolinium based MRI contrast agents have a different formulation from iodinated radiographic contrast media, and there is no known cross sensitivity between these two types of contrast. If a contrast examination is still felt necessary, premedication with corticosteroids should be performed and low osmolar contrast selected. Two accepted protocols for corticosteroid administration in this setting include 50 mg of prednisone p.o. 12,6, and 1 hour prior to the examination, or 32 mg of p.o. solumedrol 12 and 2 hours prior to the exam. Fifty mg of diphenhydramine at bedtime the evening prior and 1 hour prior to the procedure is usually also administered. The equivalent iv dose of solumedrol can be substituted if the patient is unable to tolerate p.o. administration.
Q: Aren't low-osmolar contrast agents safer?	Low osmolality contrast media (LOCM) are associated with less patient discomfort during administration. However, the risk of death from contrast reaction is felt to be mostly unchanged from that of high-osmolality contrast media (HOCM). The risk of very severe reactions is decreased with low-osmolality contrast but the amount of risk reduction in patients not at high risk for a reaction is very low. In the largest study from data on 337,000 Japanese patients who underwent contrast examination, the estimated risk of severe contrast reaction was 0.04 percent in patients receiving HOCM and 0.004 percent in patients receiving LOCM. In a separate report of 109,000 examinations, respective percentages were 0.09 percent and 0.02 percent for HOCM and LOCM. Thus, for the patient with no known risk factors for contrast reaction, HOCM are felt to be relatively safe.
Q: Why are LOCM not used routinely on all contrast examinations?	Low osmolality contrast agents are about 10 times more expensive than high-osmolality agents. At UAB, the cost of a 150 ml bottle of Conray 60, a typical high osmolality agent, used during a routine CT examination is $9.15 whereas the same dose of Optiray 320 is $94.19. This cost to the patient may not be reimbursed by a third party insurer. At University Hospital and Kirklin Clinic, all outpatients who will undergo a contrast examination are screened by the radiologic technologist for risk factors including prior reaction, history of severe allergy to any medication, active asthma, current severe cardiac disease, history of sickle cell disease or multiple myeloma, and increased risk of aspiratoin. The radiologist then selects the dose and type of contrast media after reviewing this information. By formalizing the protocol for the use of LOCM, we were able to reduce the use of LOCM at UAB from 40 percent of studies to 15 percent of studies, saving approximately $250,000, without any increase in moderate or severe reactions.
Q: Do Low-Osmolality contrast media have a lower incidence of associated nephrotoxicity?	This is controversial. Patients with insulin-dependent diabetes, volume depletion, and baseline renal dysfunction are a higher risk for contrast induced acute tubular necrosis or transient renal dysfunction. A few studies have suggested a slight benefit to use of LOCM in this setting. In our department, patients with a stable creatinine up to 2.5 mg/dl who need a contrast study are usually given LOCM. The benefits of saline infusion during a 12-hour period prior to examination, and limiting the amount of contrast infused, are better documented in the prevention of nephrotoxicity. Contrast administration in patients with rising creatinine or stable creatine greater than 2.5 mg/dl is not recommended. LOCM is also often used in the patients with end-stage renal disease, not because of concerns of nephrotoxicity but due to the possible hemodynamic effects of an osmotic load in these patients that may also commonly have cardiac disease.