Thalassemia is the most prevalent single-gene disorder globally, with around 94 million heterozygous for beta-thalassemia and 60,000 homozygotes born every year. It is a hereditary hemolytic disease resulting in abnormal hemoglobin synthesis and is common among Mediterranean populations [1]. Three types of thalassemia are classified according to their clinical severity: major, intermediate, and minor. The most serious type is thalassemia major (TM). Individuals with TM have chronic hemolytic anemia, which often needs lifelong transfusion therapy and can result in tissue iron overload. Cardiovascular complications resulting from myocardial iron overload continue to be a major reason for morbidity and death in those cases [2]. Even though survivability is increasing in cohorts of cases treated with chelation therapy at an early age [3], myocardial siderosis with subsequent heart failure continues to be major reason for mortality (50–70%) in thalassemia major cases. This disease manifests itself at an alarmingly early age with about 15–50% of cases dying before the age of 35 [3, 4]. Once clinically evident heart failure is apparent and catastrophic decline in heart function, leading to death may occur fast. Prediction of heart failure depends on actual iron loading measurements; time-averaged serum ferritin > 2500 µg/L [5, 6] and hepatic iron concentration > 15 mg/kg [7]. Nevertheless, the persistently high death rate from heart failure suggests that high-risk cases are not recognized in time for intervention strategy. Ventricular function assessment, like changes in ejection fraction over time, has also been suggested in thalassemia. However, this method detects cases relatively late [8], and the impairment may be concealed due to supranormal left ventricular performance in thalassemia cases without myocardial iron overload [9]. Of these methods, the measurement of Magnetic resonance imaging T2* (MRI T2*) has become the most often utilized in the heart due to its ease of integration with heart gating, its speed and robustness, and its sensitivity to iron deposit [10]. Cardiovascular T2* imaging is transferable, with excellent inter-scanner accuracy [11], and exhibits a good association with the invasive method of biopsy. Direct calibration of the heart and liver T2* values to myocardial and hepatic iron concentrations has been recorded in animals [12] and humans [13].
Objectives
We targeted to assess cardiac and liver iron overload in transfusion-dependent B thalassemia major (TDT) children using MRI T2*.
Methods
This prospective clinical study was done in the Radiology department at Minia Maternity and Children University Hospital in Egypt. Sixty children diagnosed with transfusion-dependent beta-thalassemia major (TDT) depending on hematological and clinical evaluation and aged between 5 and 15 years were included in the study. Recruited children were on regular blood transfusion each 2–4 weeks to keep the hemoglobin (Hb%) between 9–11 g/dl. Permission was obtained from the local ethics committee at the Faculty of Medicine, Minia University, and informed consent was collected from the guardians or parents of the children. We excluded thalassemic children younger than five years old, cases with insufficient transfusion to cause hepatic or cardiac siderosis, and cases with a condition incompatible with MRI.
All enrolled children underwent a detailed history taking, including demographic data and clinical characteristics, including age, sex, residence, and duration of the disease. Details of chelation therapy were obtained, including orally administered chelating agents as deferasirox (DFX) and deferiprone (DFP), injectable forms as subcutaneous (SC) or intravenous (IV) desferrioxamine (DFO), compliance to treatment, and regularity of their use. The duration, dose, and type of treatment, whether monotherapy or in combination, were also confirmed. The past history of splenectomy was recorded if it was done. All children were diagnosed and treated according to The Thalassemia Clinical Research Network (TCRN) guidelines [14].
Clinical examination and laboratory investigations were performed, involving kidney and liver function tests, complete blood count, ferritin levels, and serum iron. MRI of the liver and the heart was carried out in all cases.
MRI methodology and image acquisition
MRI study was done on a 1.5-Tesla MR system (Ingenia; Philips Medical Systems, the Netherlands). ECG and respiratory gating were used with dedicated phased array Torso coil using single breath-hold multi-echo gradient echo sequence as follows: 1. To begin, localizer images in three orthogonal dimensions were obtained (axial, sagittal, and coronal) SSFP (B-FFE). They are: 1. Fast single-shot scans (fast SSh). 2. Left anterior oblique (LAO) vertical long-axis view. 3. Four-chamber view (P4CH). 4. Multiecho turbo-field echo (mTFE)/fast field echo (FFE) cardiac black blood (BB) short-axis view. 5. Multiecho turbo-field echo (mTFE) Cardiac white blood (WB) short axis. 6. Multiecho turbo/fast field echo (mTFE/m-FFE) Liver FIG (Axial) Imaging field of view. 7. In short-axis view, functional cine images utilizing an ECG-gated segmented k-space breath-hold balanced turbo-field echo (b-TFE) sequence.
Postprocessing was done using region of interest-based measurement to calculate the T2* value of the heart, liver iron concentration (LIC) in mg/g dry weight, and left ventricular ejection fraction (LVEF).
Cardiac T2* and LVEF measurements
Utilizing a single breath-hold ECG-gated multi-echo dark blood method, we recorded a single short-axis midventricular slice (slice thickness: 10 mm, TR: 710 ms, FOV: 400 × 300 mm, flip angle: 20°, bandwidth: 810 Hz/Px, matrix: 256 × 96 mm). This T2* series produced a series of eight images with TEs ranging from 1.5 to 17.3 ms and a gap of 2.3 ms. Next, on each image, a region of interest (ROI) in the ventricular septum was chosen to determine the signal strength.
The end-diastolic volumes (EDV) and end-systolic volumes (ESV) of the left ventricle were determined. By applying standard software analysis techniques, endocardial borders were manually outlined at end-systole (ES) and end-diastole (ED). Volumes were calculated using the summation of the disks approach ("Simpson's rule"), which multiplied the sum of all slices by each slice thickness. Following that, the ejection fraction was determined utilizing ESV and EDV. The ejection fraction was determined utilizing a standard CMR sequence, and an EF of less than 56% was regarded to be suggestive of cardiac dysfunction.
Liver T2* measurements
The (ROI) was drawn in homogenous liver tissue from an axial mid hepatic slice of the right lobe avoiding bile ducts and blood vessels. The ROI was produced throughout all images, and signal intensity was measured using truncation and offset models (where a constant offset is applied to account for long T2* and noise components). R2* values (= 1000/T2*) were turned into LIC (mg/gdw) utilizing Garbowski’s equation [15]: LIC = 0.03 × R2 * + 0.7
According to calculated T2*, cardiac iron load in cases was classified as acceptable (T2* > 20 ms), mild (T2* 15–20 ms), moderate (T2* 10–14 ms), and severe (T2* < 10 ms) myocardial affection [16, 17]. Liver iron concentration (LIC) was classified as acceptable (˂ 3.5 mg/g) mild (3.5–7 mg/g), moderate (7–12 mg/g) and severe (> 12 mg/g) [18] (Fig. 1).
Statistical analysis
The data were analyzed utilizing the SPSS 20.0 statistical package. The Kolmogorov–Smirnov or Shapiro–Wilk tests were utilized to identify the data normality. For quantitative parametric measures, data were recorded as mean ± standard deviation (SD), minimum and maximum of range, or median and range for quantitative nonparametric measures. For parametric data, the student t test was employed; the Mann–Whitney test was used for nonparametric data. Analysis of variance (ANOVA) was employed for comparison between parametric data. To compare categorical variables, the Chi-square test or fisher's exact were utilized. Pearson's association analysis was used to determine the associations between the parameters. Association coefficients of r = 0–0.24 were regarded weak, r = 0.25–0.49 were considered fair, r = 0.5–0.74 were considered moderate, and r = 0.75–1 were considered strong. The P value of 0.05 or less was significant.