Delayed enhancement MRI

Cardiac MRI may have a role in risk stratification for SCD due to its ability to detect myocardial scar. The use of gadolinium, which accumulates in infarcted tissue, has allowed delayed enhancement MRI to detect scar burden. Early experiments in dog models performed by coronary artery occlusion compared acute and chronic infarcts to pathologic specimens of the dog heart postmortem (89,90). Delayed enhancement MRI was remarkably accurate in imaging the infarcted tissue in comparison to the pathologic specimen. The spatial extent of hyperenhancement was the same as the spatial extent of myocyte necrosis at every stage post-MI. Reversible ischemia did not show delayed gadolinium uptake. Thus, delayed enhancement MRI can distinguish between reversible and irreversible injury, and... 

Whether the presence of scar and/or the amount of scar is predictive of SCD is yet to be determined. In a study of 48 patients with CAD who were referred for EP study, infarct size was compared with LVEF, with respect to their correlation with induciblity on EP study (91). They found that patients with sustained, mono-morphic VT had larger infarcts than patients who did not have inducible arrhythmias, and patients with polymorphic VT or VF had intermediate infarct masses. Infarct mass and surface area were better predictors of inducibility of monomorphic VT than LVEF. The study was limited by its small sample size, but demonstrates that scar burden on MRI may correspond to inducibility on EP study. However, while inducibility on EP study is helpful in risk stratification of SCD, as discussed earlier even patients with a negative EP study have a high rate of future SCD. Thus, the true value of delayed enhancement MRI would be to demonstrate risk stratification beyond that of conventional methods. 

Delayed enhancement MRI may prove to be a powerful noninvasive technique that based on quantification of scar burden can risk stratify patients for SCD and select patients who may need further therapy. Ongoing trials will clarify the role of MRI in risk stratification, and whether assessment of infarct mass will supplant LVEF as the best sole risk stratification tool. 

Fig. 20.7a-d. Cross-sectional (short axis) reconstruction of a first-pass, contrast-enhanced 16-slice coronary CT angiographic dataset (a) compared with delayed-enhancement MRI (b) of an 85-year-old male patient. In the contrast-enhanced CT images, an extensive area of decreased attenuation is seen in the free lateral and parts of the basal wall of the left ventricle (a arrow). In this area of myocardium, a large myocardial in-... 

Fig. 20.8a,b. If an additional late scan is performed with CT after first-pass CTA of the heart, e.g., 15-20 min after initial contrast administration, then late enhancement effects can also be observed in CT, depicting infarcted myocardium. In these pictures from an animal model, a direct face-to-face comparison of delayed-enhancement CT (a two upper row images) versus delayed-enhancement MRI (a two lower row images) shows the different stages of early and chronic MI as visualized by... 

In delayed-phase imaging, the signal increase in the liver parenchyma does not necessarily increase the conspicuity or detection of lesions because residual hepatocytes of a tumor of hepatocytic origin, such as hepatocellular carcinoma (HCC) and focal nodular hyperplasia, may influence the contrast enhancement. Gd-BOPTA is effective for use with delayed-phase MRI to detect metastases [130]. In cirrhosis, liver functioning is impaired and the number of normal hepatocytes is reduced. The entry of Gd-BOPTA into cirrhotic hepatocytes decreases, but the accumulation in the liver increases due to reduced biliary excretion [131]. As a consequence, contrast enhancement is reduced and the window of acquisition is widened. The contrast enhancement of a cirrhotic liver is therefore different from that observed in normal liver parenchyma. 

McCann GP, Van Dockum WG, Beek AM, et al. Extent of MRI delayed enhancement of myocardial mass is related to right ventricular dysfunction in pulmonary artery hypertension. Am J Roentgenol 2007 188 349-55. 

Ibaraki, M., et al., Tracer delay correction of cerebral blood flow with dynamic susceptibility contrast-enhanced MRI. J Cereb Blood Elow Metab, 2005. 25(3) p. 378-90. 

Incompetent and dilated ovarian veins are frequently seen on CT in asymptomatic parous women (Fig. 17.11) [31]. Congenital or acquired vascular malformations of the uterus or parametria present also as vascular lesions. Contrast-enhanced CT or MRI may aid in the differentiation by the early enhancement of arteriovenous malformations in contrast to a more delayed enhancement in varicosities [32]. Adnexal masses with torsion or rare uterine tumors, especially choriocarcinomas may also be surrounded by thick, tortuous, well-enhanced vessels. The clinical background and imaging findings of an adnexal or uterine mass aid in the differential diagnosis. 

Cardiovascular In a retrospective study in 152 patients with breast cancer (mean age 52 years), 36 developed trastuzumab mediated cardiomyopathy, most were asymptomatic [169 ]. Susceptibility factors were hypertension, a history of smoking, and a family history of coronary artery disease. During the 6-month follow-up period, 34 of the patients had subepicar al linear delayed enhancement of the lateral wall of the left ventricle on MRI scan, suggesting trastuzumab-induced myocarditis. 

Fig. 59. Wedge-shaped contrast enhancement in Case 2 with ALPE in Fig. 57. a, MRI 3min after the administration of Gd-DTPA (TR120, TE4.1/1). b, Delayed CT 24 h after the administration of contrast medium. These pictures are mirror images, as indicated by the arrows (From [36], with permission)...

In the patients with ALPE, plain CT of the kidney (delayed CT) a few hours, 24 h, and 48 h after the administration of 40 ml contrast medium showed wedge-shaped contrast enhancement. When physicians hesitate to administer a contrast medium, patchy accumulation can be sometimes detected by magnetic resonance imaging (MRI) with gadolinium-diethylenetriaminopentoacetic acid (Gd-DTPA), bone scan with MDP, or ultrasonography with Levovist. 

Preliminary studies of collateral circulation in high grade stenoses or occlusions using ultra fast dynamic MRA with temporal resolution in the range of a second did show delayed contrast enhancement in the affected vascular territory, but did not provide relevant additional information compared with conventional MRI and perfusion techniques probably due to the reduced spatial resolution (Wetzel et al. 2001). A dedicated analysis of collateral circulations, especially extra-intracranially, is still the domain of DSA as far as the exact depiction of anatomical connections is of importance. If the exact anastomotic vascular anatomy is not of primary interest, the collateral supply is better determined by MR perfusion techniques. 

Cherryman GR, Pirovano G, Kirchin MA. Gadobenate dimeglumine in MRI of acute myocardial infarction results of a phase III study comparing dynamic and delayed contrast enhanced magnetic resonance imaging with EKG, (201)T1 SPECT, and echocardiography. Invest Radiol 2002 37(3) 135-45. 

Kim RJ, Fieno DS, Parrish TB, et al. Relationship of MRI delayed contrast enhancement to irreversible injury, infarct age, and contractile function. Circulation 1999 100(19) 1992-2002. 

In orthotopically transplanted murine models of brain tumors, cross-section micro-MRI at 11.7 T allows for visualization and measurement of the physically inaccessible tumors. To allow for long resident times of a contrast agent in the tumor, intraperitoneal administration was used as a route of injection for contrast-enhanced micro-MRI, and a simple method for relative tumor volume measurements was examined. A strategy for visualizing the variability of the delayed tumor enhancement was developed. These strategies were applied to monitor the growth of brain tumors xenotransplanted into nude mice and either treated with the antiangiogenic peptide EMD 121974 or an inactive control peptide. 

Differential diagnosis includes solid ovarian tumors in younger age, e.g., granulosa cell tumors and teratomas. In MRI, uterine fibroma and fibrothecoma may display a similar appearance on T2-weighted images however, contrast enhancement in these tumors is less and delayed. Especially in CT, differentiation of subserosal uterine fibroids from solid dysgerminomas is not possible. 

Contrast enhancement has not been described as a characteristic feature of cavernomas of the CNS in the CT era. Because of the improved contrast resolution of MRI (compared to CT), contrast enhancement is much more visible. However, MRI does not overcome the problem created by the slow blood exchange between the normal blood and the dilated cavernous vessels. Specifically with fast Tl-weighted sequences it is necessary to delay the interval between contrast agent injection and the start of the scanning procedure. 

Although being generally based on CRE techniques, the various clinical applications differ substantially. The major applications of CRE techniques include analysis of cardiac function, using cine techniques, assessment of blood flow based on cine phase-contrast (PC) sequences and myocardial perfusion, as well as delayed contrast enhancement imaging. These different applications are discussed separately within the clinical aspects of cardiac CT and MRI. 

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