Christina L. Tosti

Myocardial T2 quantitation in patients with iron overload at 3 Tesla

To investigate the feasibility of measuring myocardial T2 at 3 Tesla for assessment of tissue iron in thalassemia major and other iron overloaded patients.

Preliminary validation of angle-independent myocardial elastography using MR tagging in a clinical setting.

Myocardial elastography (ME), a radio-frequency (RF) based speckle tracking technique, was employed in order to image the entire two-dimensional (2D) transmural deformation field in full echocardiographic views and was validated against tagged magnetic resonance imaging (tMRI) in normal as well as reperfused (i.e., treated myocardial infarction [MI]) human left ventricles. RF ultrasound and tMRI frames were acquired at the papillary muscle level in 2D short-axis (SA) views at the frame rates of 136 (fps; real-time) and 33 fps (electrocardiogram [ECG]-gated), respectively. In ME, in-plane, 2D (lateral and axial) incremental displacements were iteratively estimated using one-dimensional (1D) cross-correlation and recorrelation techniques in a 2D search with a 1D matching kernel. In tMRI, cardiac motion was estimated by a template-matching algorithm on a 2D grid-shaped mesh. In both ME and tMRI, cumulative 2D displacements were obtained and then used to estimate 2D Lagrangian finite systolic strains, from which polar (i.e., radial and circumferential) strains, namely angle-independent measures, were further obtained through coordinate transformation. Principal strains, which are angle-independent and less centroid-dependent than polar strains, were also computed and imaged based on the 2D finite strains using methodology previously established. Both qualitatively and quantitatively, angle-independent ME is shown to be capable of (1) estimating myocardial deformation in good agreement with tMRI estimates in a clinical setting and of (2) differentiating abnormal from normal myocardium in a full left-ventricular view. The principal strains were concluded to be a potential diagnostic measure for detection of cardiac disease with reduced centroid dependence.

Separate MRI Quantification of Dispersed (Ferritin-like) and Aggregated (Hemosiderin-like) Storage Iron

A new MRI method is proposed for separately quantifying the two principal forms of tissue storage (nonheme) iron: ferritin iron, a dispersed, soluble fraction that can be rapidly mobilized, and hemosiderin iron, an aggregated, insoluble fraction that serves as a long‐term reserve. The method utilizes multiple spin echo sequences, exploiting the fact that aggregated iron can induce nonmonoexponential signal decay for multiple spin echo sequences. The method is validated in vitro for agarose phantoms, simulating dispersed iron with manganese chloride, and aggregated iron with iron oxide microspheres. To demonstrate feasibility for human studies, preliminary in vivo data from two healthy controls and six patients with transfusional iron overload are presented. For both phantoms and human subjects, conventional R2 and R2* relaxation rates are also measured in order to contrast the proposed method with established MRI iron quantification techniques. Quantification of dispersed (ferritin‐like) iron may provide a new means of monitoring the risk of iron‐induced toxicity in patients with iron overload and, together with quantification of aggregated (hemosiderin‐like) iron, improve the accuracy of estimates for total storage iron. Magn Reson Med 63:1201–1209, 2010.

Magnetic resonance assessment of iron overload by separate measurement of tissue ferritin and hemosiderin iron

With transfusional iron overload, almost all the excess iron is sequestered intracellularly as rapidly mobilizable, dispersed, soluble ferritin iron, and as aggregated, insoluble hemosiderin iron for long‐term storage. Established magnetic resonance imaging (MRI) indicators of tissue iron (R2, R2*) are principally influenced by hemosiderin iron and change slowly, even with intensive iron chelation. Intracellular ferritin iron is evidently in equilibrium with the low‐molecular‐weight cytosolic iron pool that can change rapidly with iron chelation. We have developed a new MRI method to separately measure ferritin and hemosiderin iron, based on the non‐monoexponential signal decay induced by aggregated iron in multiple‐spin‐echo sequences. We have initially validated the method in agarose phantoms and in human liver explants and shown the feasibility of its application in patients with thalassemia major. Measurement of tissue ferritin iron is a promising new means to rapidly evaluate the effectiveness of iron‐chelating regimens.

Time-of-flight magnetic resonance angiography of the canine brain at 3.0 Tesla and 7.0 Tesla.

OBJECTIVE To evaluate the ability of 2-D time-of-flight (ToF) magnetic resonance angiography (MRA) to depict intracranial vasculature and compare results obtained with 3.0- and 7.0-T scanners in dogs. ANIMALS 5 healthy Beagles. PROCEDURES 2-D ToF-MRA of the intracranial vasculature was obtained for each dog by use of a 3.0-T and a 7.0-T scanner. Quantitative assessment of the images was obtained by documentation of the visibility of major arteries comprising the cerebral arterial circle and their branches and recording the number of vessels visualized in the dorsal third of the brain. Qualitative assessment was established by evaluation of overall image quality and image artifacts. RESULTS Use of 3.0- and 7.0-T scanners allowed visualization of the larger vessels of the cerebral arterial circle. Use of a 7.0-T scanner was superior to use of a 3.0-T scanner in depiction of the first- and second-order arterial branches. Maximum-intensity projection images had a larger number of vessels when obtained by use of a 7.0-T scanner than with a 3.0-T scanner. Overall, image quality and artifacts were similar with both scanners. CONCLUSIONS AND CLINICAL RELEVANCE Visualization of the major intracranial arteries was comparable with 3.0- and 7.0-T scanners; the 7.0-T scanner was superior for visualizing smaller vessels. Results indicated that ToF-MRA is an easily performed imaging technique that can be included as part of a standard magnetic resonance imaging examination and should be included in the imaging protocol of dogs suspected of having cerebrovascular disease.

Methods for noninvasive measurement of tissue iron in Cooley's anemia

Abstract: To examine the relationship between myocardial storage iron and body iron burden, as assessed by hepatic storage iron measurements, we studied 22 patients with transfusion‐dependent thalassemia syndromes, all being treated with subcutaneous deferoxamine, and 6 healthy subjects. Study participants were examined with a Philips 1.5‐T Intera scanner using three multiecho spin echo sequences with electrocardiographic triggering and respiratory navigator gating. Myocardial and hepatic storage iron concentrations were determined using a new magnetic resonance method that estimates total tissue iron stores by separately measuring the two principal forms of storage iron, ferritin and hemosiderin. In a subset of 10 patients with β‐thalassemia major, the hepatic storage iron concentration had been monitored repeatedly for 12‐14 years by chemical analysis of tissue obtained by liver biopsy and by magnetic susceptometry. In this subset, we examine the relationship between hepatic iron concentration over time and our current magnetic resonance estimates of myocardial iron stores. No significant relationship was found between simultaneous estimates of myocardial and hepatic storage iron concentrations. By contrast, in the subset of 10 patients with β‐thalassemia major, the correlation between the 5‐year average of hepatic iron concentration and the current myocardial storage iron was significant (R= .67, P= .03). In these patients, myocardial storage iron concentrations seem to reflect the control of body iron over a period of years. Magnetic resonance methods promise to provide more effective monitoring of iron deposition in vulnerable tissues, including the liver, heart, and endocrine organs, and could contribute to the development of iron‐chelating regimens that more effectively prevent iron toxicity.

Validation of myocardial elastography using MR tagging in normal and abnormal human hearts in vivo

In this paper, myocardial elastography (ME), a radio-frequency (RF) based speckle tracking technique, was employed in order to assess the contractility of a myocardium, and validated against tagged magnetic resonance imaging (tMRI) in vivo in normal as well as abnormal cases. Both RF ultrasound and tMRI frames were acquired in 2D short-axis (SA) views from two healthy subjects and one with a history of infarction. In-plane (lateral and axial) incremental displacements were iteratively estimated using 1D cross-correlation and recorrelation techniques in a 2D search with a 1D matching kernel. The incremental displacements from end-diastole (ED) to end-systole (ES) were then accumulated to obtain cumulative systolic displacements. In tMRI, cardiac motion was obtained by a template-matching algorithm on a 2D grid-shaped mesh. The entire displacement distribution within the myocardium was obtained by a cubic B-splinebased method. In both ME and tMRI, 2D Lagrangian finite systolic strains were calculated from cumulative 2D displacements. Radial and circumferential strains were then computed from the 2D finite strains. Both qualitatively and quantitatively, ME is shown capable of measuring myocardial deformation in excellent agreement with tMRI estimates in normal and abnormal subjects