Yousef W. Nielsen

Unenhanced MR Imaging in adults with clinically suspected acute appendicitis

PURPOSE The purpose of the study was to evaluate unenhanced Magnetic Resonance Imaging (MRI) for the diagnosis of appendicitis or another surgery-requiring condition in an adult population scheduled for emergency appendectomy based on a clinical diagnosis of suspected acute appendicitis. MATERIALS AND METHODS The prospective study included 48 consecutive patients (29 female, 19 male, 18-70 years old, mean age=37.1 years). MRI examination was designed to be comfortable and fast; no contrast was administered. The sequences were performed during quiet respiration. The MRI findings were reviewed by two radiologists and one surgeon independent of each other and compared with surgical and pathological records. RESULTS According to the surgical and histopathological findings 30 of 48 patients (63%) had acute appendicitis. Of the remaining 18 patients, 4 patients had no reasons for the clinical symptoms and 14 patients had other pathology. For the three reviewers the performance of MRI in the diagnosis of acute appendicitis showed the following sensitivity, specificity and accuracy ranges: 83-93%, 50-83% and 77-83%. Moderate (κ=0.51) and fair (κ=0.31) interobserver agreements in the MR diagnosis of acute appendicitis were found between the reviewers. Sensitivity, specificity and accuracy values for overall performance of MRI in detecting pelvic abnormalities were 100%, 75% (3 of 4 healthy patients were identified by MRI) and 98%, respectively. CONCLUSION Unenhanced fast MRI is feasible as an additional fast screening before the appendectomy. It may prevent unnecessary surgeries. The fast MRI examination can be adequately performed on an MRI unit of broad range of field strengths.

Contrast-enhanced peripheral MRA: technique and contrast agents.

In the last decade contrast-enhanced magnetic resonance angiography (CE-MRA) has gained wide acceptance as a valuable tool in the diagnostic work-up of patients with peripheral arterial disease. This review presents current concepts in peripheral CE-MRA with emphasis on MRI technique and contrast agents. Peripheral CE-MRA is defined as an MR angiogram of the arteries from the aortic bifurcation to the feet. Advantages of CE-MRA include minimal invasiveness and lack of ionizing radiation. The basic technique employed for peripheral CE-MRA is the bolus-chase method. With this method a paramagnetic MRI contrast agent is injected intravenously and T1-weighted images are acquired in the subsequent arterial first-pass phase. In order to achieve high quality MR angiograms without interfering venous contamination or artifacts, a number of factors need to be taken into account. This includes magnetic field strength of the MRI system, receiver coil configuration, use of parallel imaging, contrast bolus timing technique, and k-space filling strategies. Furthermore, it is possible to optimize peripheral CE-MRA using venous compression techniques, hybrid scan protocols, time-resolved imaging, and steady-state MRA. Gadolinium(Gd)-based contrast agents are used for CE-MRA of the peripheral arteries. Extracellular Gd agents have a pharmacokinetic profile similar to iodinated contrast media. Accordingly, these agents are employed for first-pass MRA. Blood-pool Gd-based agents are characterized by prolonged intravascular stay, due to macromolecular structure or protein binding. These agents can be used for first-pass, as well as steady-state MRA. Some Gd-based contrast agents with low thermodynamic stability have been linked to development of nephrogenic systemic fibrosis in patients with severe renal insufficiency. Using optimized technique and a stable MRI contrast agent, peripheral CE-MRA is a safe procedure with diagnostic accuracy close to that of conventional catheter X-ray angiography.

Whole-body MR Angiography with Body Coil Acquisition at 3 T in Patients with Peripheral Arterial Disease Using the Contrast Agent Gadofosveset Trisodium1

RATIONALE AND OBJECTIVES Whole-body magnetic resonance angiography (WB-MRA) at 3 T with body coil acquisition has not previously been investigated. In this study, WB-MRA was performed in this manner using the blood pool contrast agent gadofosveset trisodium. MATERIALS AND METHODS Eleven consecutive patients (five men, six women) with symptomatic peripheral arterial disease (two with critical limb ischemia, nine with claudication) were examined. Conventional digital subtraction angiography (DSA) of the aorta and the inflow and runoff arteries was used as the reference method. WB-MRA was performed using four slightly overlapping stations covering the arteries from the neck to the ankles. The arterial system was divided into 42 segments that were analyzed for the presence of significant arterial disease (> or =50% luminal narrowing or occlusion) by two blinded observers. RESULTS Sensitivities for detecting a significant arterial lesion with WB-MRA using gadofosveset as the contrast agent were 0.66 (95% confidence interval [CI], 0.49-0.79) and 0.68 (95% CI, 0.52-0.81) for the two observers. Specificities were 0.82 (95% CI, 0.74-0.88) and 0.93 (95% CI, 0.87-0.96), respectively. Intermodality agreement between WB-MRA and DSA was moderate to good, with overall kappa values of 0.44 (95% CI, 0.29-0.59) and 0.63 (95% CI, 0.5-0.77) for the two observers. Interobserver agreement for WB-MRA was good, at kappa = 0.60 (95% CI, 0.50-0.71). CONCLUSION WB-MRA at 3 T with body coil acquisition in patients with peripheral arterial disease showed good reproducibility but only moderate to good agreement with DSA. Further assessment of the methods clinical application is warranted.

Optimal management of acute nonrenal adverse reactions to iodine-based contrast media

Acute adverse reactions to iodine-based contrast media occur within 60 minutes of administration. The reactions range from mild (flushing, arm pain, nausea/vomiting, headache) to moderate (bronchospasm, hypotension), and severe (cardiovascular collapse, laryngeal edema, convulsions, arrhythmias). Most acute adverse reactions occur in an unpredictable manner. Use of the older group of ionic iodine-based contrast agents increases the risk of acute adverse reactions. Other risk factors include previous reactions to contrast media, asthma, and allergic conditions. The exact pathophysiology of the acute adverse reactions is unknown, but some of the reactions are pseudoallergic mimicking type 1 allergic reactions. As antibodies against contrast media have not been consistently demonstrated, the reactions are, in most cases, not truly allergic in nature. Most of the severe and fatal adverse reactions occur within the first 20 minutes after injection. Thus, it is important that patients are observed in the radiology department during this period. The radiologist should be near the room where contrast media is administered, and be ready to treat any acute nonrenal adverse reaction. Appropriate drugs and resuscitation equipment should be in/near the room where the contrast media is administered. The important first-line management of acute adverse reactions includes the establishment of an adequate airway, oxygen supplementation by mask, intravenous fluid administration, and measurement of blood pressure and heart rate. When severe anaphylactoid reactions occur, adrenaline should be given intramuscularly. Only one concentration of adrenaline (1:1000-1 mg/mL) should be available in the radiology department to avoid dosing errors in stressful acute settings. Resuscitation team specialists should be the only ones giving intravenous adrenaline. It is important that all radiologists maintain the capability of performing first-line treatment of acute adverse reactions

Patient acceptance of whole-body magnetic resonance angiography: A prospective questionnaire study

Background: Whole-body magnetic resonance angiography (WB-MRA) is a noninvasive method for diagnosing the systemic distribution of atherosclerosis. Numerous studies have demonstrated the feasibility and diagnostic performance of WB-MRA, but no studies have investigated patient acceptance of this imaging method. Purpose: To measure patient acceptance of WB-MRA compared to the gold standard, digital subtraction angiography (DSA), in patients with peripheral arterial disease (PAD). Material and Methods: In a prospective design, 79 consecutive patients (51 male, mean age 67 years) with symptomatic PAD, scheduled to undergo both WB-MRA and DSA, were included. Patient acceptance of each imaging procedure was assessed with a postal questionnaire (13 questions). A five-point rank scale (1, no discomfort; 5, severe discomfort) was used to grade patient discomfort. Results: One patient was excluded from data analysis (did not undergo DSA). Of the remaining 78 patients, 69 completed the questionnaire (response rate 88%). Overall discomfort scores were higher in DSA compared to WB-MRA (mean 2.1 and 1.7, respectively; P = 0.06). In WB-MRA, overall discomfort was strongly correlated to feeling confined in the MRI system (R = 0.77, P< 0.001). In DSA, discomfort was strongly correlated to arterial puncture (R = 0.66, P< 0.001) and contrast injection (R= 0.65, P< 0.001). Injection of iodinated contrast agent at DSA was graded more uncomfortable than injection of gadolinium-based contrast agent at WB-MRA (mean 2.1 vs. 1.5, respectively; P<0.001). Sixty-two patients (90%) were willing to repeat WB-MRA, and 64 patients (93%) would repeat DSA if they needed another vascular examination. Forty-one patients preferred WB-MRA (60%), 12 patients preferred DSA (17%), and 16 patients had no preference (23%). Patient preference of WB-MRA over DSA was statistically significant (P< 0.001). Conclusion: Patient acceptance of WB-MRA is superior to that of DSA in patients with PAD, with the majority of patients preferring WB-MRA.

Imaging in Chronic Kidney Disease

Imaging in patients with reduced kidney function (glomerular filtration rate) raises three problems. (1) The imaging procedures (e.g., renography, CT urography, MR urography), where excretion of contrast media/isotopes is an integrated part of the examination, cannot give useful images in patients with <~30 ml/min/1.73 m2; all other procedures can be done. (2) Administration of iodine-based contrast media may cause a temporary (in most cases) decrease in kidney function (contrast nephropathy). (3) Injection of gadolinium-based contrast media may induce nephrogenic systemic fibrosis. Awareness of these issues is of utmost importance, when one takes care of patients with a glomerular filtration rate below 60 ml/min/1.73 m2. One should never deny a patient a clinically well-indicated imaging examination due to fear of contrast nephropathy or nephrogenic systemic fibrosis; denying may cause one overlooking, e.g., a tumor at a time where it might be removed. In patients with moderate or severe renal insufficiency, the relative low risk of nephrogenic systemic fibrosis against the relative high risk of intermittent contrast nephropathy should be taken into consideration before enhanced imaging; contrast nephropathy is seen after all agents, whereas nephrogenic systemic fibrosis does not occur after all agents.

Contrast Media Administration: Safety Issues and Legal Aspects

Contrast media (CM) are commonly used in radiological procedures such as radiography, computed tomography (CT), and magnetic resonance imaging (MRI) to enhance the differences between structures or fluids within the body tissue. There are various types of CM, and their chemical and physical properties determine their specific application.