Quantitative T2* imaging of iron overload in a non-dedicated center - Normal variation, repeatability and reader variation

Background

Patients with transfusion dependent anemia are at risk of complications from iron overload. Quantitative T2* magnetic resonance imaging (MRI) is the best non-invasive method to assess iron deposition in the liver and heart and to guide chelation therapy.

Purpose

To investigate the image quality and inter-observer variations in T2* measurements of the myocardium and the liver, and to obtain the lower limit of cardiac and hepatic quantitative T2* values in patients without suspicion of iron overload.

Material and methods

Thirty-eight patients referred for cardiac MRI were prospectively included in the study. Three patients were referred with, and 35 without suspicion of iron overload. Quantitative T2* parametric maps were obtained on a 1.5 T MRI system in the cardiac short axis and liver axial view. Two readers independently assessed the image quality and the representative and the lowest T2* value in the myocardium and the liver.

Results

The normal range of representative T2* values in the myocardium and liver was 24−45 ms and 14−37 ms, respectively. None of the 35 participants (0 %, 95 % confidence interval 0–11 %) in the normal reference group demonstrated representative T2* values below previously reported lower limits in the myocardium (20 ms) or the liver (8 ms). Focal myocardial areas with T2* values near the lower normal range, 19−20 ms, were seen in two patients. The readers generally reported good image quality.

Conclusion

T2* imaging for assessing iron overload can be performed in a non-dedicated center with sufficient image quality.

Minimizing contrast media dose in CT pulmonary angiography with high-pitch technique

OBJECTIVES

To perform CT pulmonary angiography (CTPA) using a minimal amount of iodinated contrast media.

METHODS

47 patients (25 females) with mean age 69 years (range 41-82 years) referred for contrast-enhanced chest CT were prospectively included in this Phase IV clinical drug trial. All participants underwent a study specific CTPA in addition to the chest CT. The participants received 80 mg I/kg body weight Iohexol contrast media using a preparatory saline bolus, a dual flow contrast/saline bolus and a saline flush, and a scanner protocol with 80 kVp dual source high-pitch mode. Three readers independently assessed the image quality on the 3-point scale non-diagnostic, adequate or good-excellent image quality. Additionally, the pulmonary arterial contrast opacification was measured.

RESULTS

On average, the patients received 16.8 ml Iohexol 350 mg I/mL (range 12-20 ml). Mean patient weight was 71 kg (range 50-85 kg). Identically for all readers, pulmonary embolism (PE) was detected in 1/47 participants. The median number of examinations visually scored concerning pulmonary embolism as good-excellent was 47/47 (range 44-47); adequate 0/47 (0-3) and non-diagnostic 0/47 (range 0-0). The proportion adequate or better examinations was for all readers 47/47, 100% [95% confidence interval 92-100%]. The mean attenuation ± standard deviation in the pulmonary trunk was 325 ± 72 Hounsfield unit (range 165-531 Hounsfield unit).

CONCLUSIONS

Diagnostic CTPA with 17 ml contrast media is possible in non-obese patients using low kVp, high pitch and carefully designed contrast media administration.

ADVANCES IN KNOWLEDGE

By combining several procedures in a CTPA protocol, the contrast media dose can be minimized.

Mild thickening of the aortic wall: subtle intramural hematoma?

Recently published criteria for the diagnosis of intramural hematoma (IMH) of the ascending aorta by transesophageal echocardiogram (TEE) include the presence of a crescent-shaped thickening of the aortic wall of more than 7 mm with an echolucent space. We report a patient whose clinical presentation suggested aortic dissection but whose TEE failed to meet the conventional criteria for such a diagnosis. TEE showed a uniform intimal thickening suspicious of IMH but less than 7 mm in thickness and with no echofree space. One week later, the patient developed frank aortic dissection.

CONCLUSION

IMH can present with a subtle echo appearance. The diagnosis should not be totally discounted in the absence of a 7-mm crescentic wall thickness and an echofree space if the clinical presentation is suggestive of dissection.

Renin expression in renal proximal tubule

Angiotensinogen, angiotensin-converting enzyme, and renin constitute the components of the renin-angiotensin system. The mammalian renal proximal tubule contains angiotensinogen, angiotensin-converting enzyme, and angiotensin receptors. Previous immunohistochemical studies describing the presence of renin in the proximal tubule could not distinguish synthesized renin from renin trapped from the glomerular filtrate. In the present study, we examined the presence of renin activity and mRNA in rabbit proximal tubule cells in primary culture and renin mRNA in microdissected proximal tubules. Renin activity was present in lysates of proximal tubule cells in primary culture. Cellular renin content in cultured proximal tubule cells was increased by incubation with 10(-5) M isoproterenol and 10(-5) M forskolin by 150 and 110%, respectively. In addition, renin transcripts were detected in poly(A)+ RNA from cultured proximal tubule cells by RNA blots under high stringency conditions. In microdissected tubules from normal rats, renin mRNA was not detectable with reverse transcription and polymerase chain reaction. However, in tubules from rats administered the angiotensinogen-converting-enzyme inhibitor, enalapril, renin was easily detected in the S2 segment of the proximal tubule. We postulate the existence of a local renin-angiotensin system that enables the proximal tubule to generate angiotensin II, thereby providing an autocrine system that could locally modulate NaHCO3 and NaCl absorption.