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The use of contrast media for cardiac imaging becomes increasing as the widespread of cardiac CT and cardiac MR. A radiologist needs to carefully consider the indication and the injection protocol of contrast media to be used as well as the possibility of adverse effect. There are several guidelines for contrast media in western countries. However, these are focusing the adverse effect of contrast media. The Asian Society of Cardiovascular Imaging, the only society dedicated to cardiovascular imaging in Asia, formed a Working Group and created a guideline, which summarizes the integrated knowledge of contrast media for cardiac imaging. In cardiac imaging, coronary artery evaluation is feasible by non-contrast MR angiography, which can be an alternative examination in high risk patients for the use of iodine contrast media. Furthermore, the body habitus of Asian patients is usually smaller than that of their western counterparts. This necessitates modifications in the injection protocol and in the formula for calculation of estimated glomerular filtration rate. This guideline provided fundamental information for the use of contrast media for Asian patients in cardiac imaging.
As the use of contrast media in cardiac imaging is becoming more common, a radiologist needs to carefully consider the indication and the injection protocol of contrast media to be used as well as the possibility of adverse effect. There are several guidelines focusing the adverse effect of contrast media [1, 2]. However, there is no guideline, which summarizes the integrated knowledge of contrast material for cardiac imaging, especially for patients of Asian origin. In cardiac imaging, coronary artery evaluation is feasible by non-contrast MR angiography, which can be an alternative examination in high risk patients for the use of iodine contrast media. Furthermore, the body habitus of Asian patients is usually smaller than that of their western counterparts. This necessitates modifications in the injection protocol and in the formula for calculation of estimated glomerular filtration rate (eGFR) [3, 4]. The major purpose of this manual is to provide fundamental information for the use of contrast media for Asian patients in cardiac imaging.
For the usage of contrast material, the basic knowledge for contrast material injection is very important to obtain optimal contrast images. The knowledge for adverse reaction is inevitable for the safe patient care. Among several adverse reactions, contrast induced nephropathy (CIN) is almost specific to iodinated contrast media, while nephrogenic systemic fibrosis (NSF) is specific to gadolinium contrast media. On the other hands, adverse reactions other than CIN and NSF is similar in both iodinated and gadolinium contrast material. Thus, this guideline consists of four chapters; (1) general rule for contrast material injection, (2) adverse reaction of iodinated and gadolinium contrast material, (3) contrast induced nephropathy and (4) nephrogenic systemic fibrosis.
Contrast enhancement in a given patient is determined by 3 factors: contrast material flow rate (ml/s), contrast material volume (ml) and contrast material iodine concentration (mg/ml) . The overall contrast volume is calculated as the injection rate multiplied by the injection duration. Warming of contrast agent prior to injection decreases viscosity and allows higher injection rates at lower injection pressures.
Accurate timing of the scan with respect to the arrival of the intravenous (IV) contrast in the target structures is necessary. Thus, the usage of either bolus tracking or a test bolus protocol is recommended.
Gadolinium based contrast media (GBCM) shorten T1 relaxation times and thus lead to higher signal intensity on T1-weighted images. Although first-pass kinetics and late distribution of GBCM are similar to those of iodinated contrast materials for CT; there are two distinct characteristics in GBCM compared to iodinated contrast materials. First, the signal intensities are not proportional to GBCM concentration due to substantial signal loss caused by T2-shortening effect at high concentrations of GBCM. Therefore, the concentration of GBCM in the blood pool or myocardium cannot be calculated directly from the signal intensity on MRI . Second, due to the much smaller contrast volume required for first-pass imaging, improving effect of high injection rate on bolus profile is limited for MRI compared to CT . For example, when you administer a single dose of GBCM to a patient with 50 kg body weight (i.e. 10 ml), increasing injection rate from 4 to 5 ml/s shortens the injection duration only slightly (i.e. 0.5 s).
The injection protocol for myocardial perfusion MRI is usually used as a dose of 0.05–0.1 mmol/kg with injection rate of 3–7 ml/s, followed by at least 30 ml saline flush (5–7 ml/s). For delayed gadolinium enhancement MRI, a total dose of 0.1–0.2 mmol/kg is administered.
Before the administration of contrast media, the referring physician and the radiologist should consider the following issues: (1) Assessment of patient risk versus potential benefit of the contrast-assisted examination. (2) Imaging alternatives that would provide the same or better diagnostic information. (3) Prevention of adverse events.
A general category that deserves attention is emotional state. There is anecdotal evidence that severe adverse effects to contrast media or to procedures can be mitigated at least in part by reducing anxiety. It may be useful, therefore, to determine whether a patient is particularly anxious and it is important to reassure and calm that patient before contrast injection .
Type of injuries
To reduce the risk
Adverse reactions are classified into acute and delayed reactions . Acute reactions are those that occur up to 1 h after the administration of CM. The majority of the delayed reactions occur between 1 and 72 h after the administration of contrast media. Subsequently occurring reactions are rare; the maximum interval is 7 days .
Contrast medium nephrotoxicity (renal adverse reactions) is mostly associated with iodinated contrast media. The risk of nephrotoxicity is very low when gadolinium contrast media are used in approved doses.
The risk of nephrotoxicity is related to the degree of pre-existing renal disease and hydration. Clinically significant nephrotoxicity after administration of iodinated contrast media is highly unusual in patients with normal renal function. There is no standard definition for reporting contrast-induced nephrotoxicity (CIN). Definitions used have included percent change in the baseline serum creatinine (e.g., a 20–50% rise in serum creatinine) and absolute elevation from baseline (0.5–2.0 mg/dl) [40, 41].
The clinical course of CIN depends on baseline renal function, coexisting risk factors, degree of hydration, and other factors. Serum creatinine usually begins to rise within the first 24 h following IV contrast media administration, peaks within 96 h (4 days), and usually returns to baseline within 7–10 days . It is unusual for patients to develop permanent renal failure, and this usually occurs in the setting of multiple risk factors.
Nephrogenic systemic fibrosis (NSF) is recently reported adverse effect specific to gadolinium contrast media. Fewer cases of NSF have been reported in Asia, as compared to the US or Europe . NSF is a severe, usually progressive, potentially fatal, systemic fibrotic disease, affecting the dermis, subcutaneous fasciae and striated muscles. In 2006 several groups noted a strong association between gadolinium-based contrast media (GBCM) administration and the disease . In many cases, affected patients had been injected with more than one type of GBCM prior to symptoms onset. However, it must be emphasized that the frequency with which NSF has been associated with different GBCM may also have been affected if the agents were used at higher doses compared to what is recommended in their package inserts. It is advisable to use the GBCM agents within their prescribed dosages and not to overdose the patient. Risk factors for nephrogenic systemic fibrosis are given in Table 7.
The etiology of NSF is still unknown but is thought to be multifactorial. The prevailing theory regarding gadolinium and NSF is that gadolinium (Gd3+) ions are released from the Gd-chelate complex of MRI contrast agents and accumulate in tissues such as skin, thereby initiating what some have described as a “toxic” reaction. The precise pathomechanism is not yet known .
It is estimated that patients with eGFR < 30 ml/min/1.73 m2 have a 1–7% chance of developing NSF after exposure to GBCM [52, 54]. All patients should be questioned for a history of renal disease. The measurement of an eGFR within 6 weeks of the GBCM study is recommended in patients with renal disease in anyone over 60 years of age, or in patients with hypertension, diabetes mellitus.
Non-contrast MR angiography is recommended for the evaluation of coronary artery. The use of CT angiography is also possible. If a contrast-enhanced MRI examination must be performed such as for the evaluation of perfusion or delayed enhancement, avoidance of the use of those GBCM that have been most frequently associated with NSF [gadodiamide (Omniscan®), gadopentetate dimeglumine (Magnevist®) and gadoversetadmide (OptiMARK®]) is recommended. Also, use of the lowest possible dose needed to obtain a diagnostic study is suggested. GBCM-enhanced MRI exams is recommended to be performed shortly before dialysis, as prompt post-procedural dialysis may reduce the likelihood that NSF will develop, although this has not been proved definitively to date .
It is recommended that any contrast media administration be avoided if at all possible. If MRI contrast media administration is absolutely essential, judicious use of the lowest possible doses of selected GBCM (avoidance of the use of those GBCM that have been most frequently associated with NSF) is probably safest .
To the best of our knowledge this is the first comprehensive guide on use of contrast media amongst Asians for cardiac imaging. In summary this manual provides basic information for the use of contrast media for Asian patients in cardiac imaging. In addition to general principles of contrast material injection we have also discussed associated adverse events like contrast induced nephropathy and nephrogenic systemic fibrosis.
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