Evaluation of Liver Iron Deposition in Transfusion-Dependent Patients By Dual-Energy CT

[Introduction]

The launch of the oral iron chelator "Deferasirox" has improved the outcomes of blood transfusion-dependent patients with iron overload in the last decade. Although serum ferritin (SF) remains the mostly commonly used metric to monitor body iron stores for decisions regarding the indication of iron chelate therapy, it is known to be affected by many factors. The liver iron concentration (LIC) is considered to be an indicator of total body iron stores, and the MR imaging-based R2 technique is the standard non-invasive technique used to evaluate LIC. However, this technique is not used in every institution due to some limitations such as its high cost and the requirement for special software. Although the application of CT, which is easy to use and inexpensive, needs to be considered for the evaluation of LIC, the use of conventional single energy CT (SECT) to measure LIC is also limited by normal variations in CT attenuation, predominantly in patients with mild iron overload. Moreover, SECT fails to detect iron in fatty livers, which has an inverse effect on attenuation by lowering CT numbers. Dual-energy CT (DECT) is a technique that is employed to obtain precise information on tissue composition and may be useful for monitoring LIC. It is based on substances showing different densities with two different energies, with each substance displaying its own energy-dependent change in CT attenuation. The role of DECT in monitoring LIC has not yet been clarified in blood transfusion-dependent patients with iron overload. We herein evaluated iron deposition in the livers of blood transfusion-dependent patients using DECT.

[Patients and Methods]

Seventeen blood transfusion-dependent patients underwent liver DECT using a dual-source 128-slice CT system, and SF levels were measured at same time. DECT images were acquired using a tube voltage pair of 140 kV and 80 kV or 140 kV and 100 kV, and the three-material decomposition of fat, soft tissue, and iron.

[Results]

The median age of patients was 52 years (range, 25 to 66), and 8 patients were male. Eight patients with AML, 3 with MDS, and 1 each with ALL, lymphoma, aplastic anemia, Evans syndrome, congenital dyserythropoietic anemia, and chronic renal failure underwent DECT. Nine patients had undergone stem cell transplantation before DECT, and 3 were receiving iron chelate therapy. The total number of units of blood transfused was available in 11 out of 17 patients. The median number of units given was 66 (range, 36 to 150). The median SF level was 2346 ng/ml (range, 569 to 7875). We divided patients into three groups based on SF levels: high >3000 ng/ml, intermediate 1000~3000 ng/ml, low <1000 ng/ml. Five patients were classified into the high SF group (range, 3765-7875 ng/ml), 8 into the intermediate SF group (1645-2916), and 4 into the low SF group (569-1240). Four patients in high, 4 in the intermediate, and 2 in the low SF groups showed diffuse iron deposition in the liver on DECT images. One patient in the high, 2 in the intermediate, and 2 patients in the low SF groups showed focal iron deposition in the left lobe of the liver. On the other hand, two patients in the intermediate SF group did not show iron deposition on DECT images. We then divided patients into two groups based on the number of units of blood transfused: 6 patients were classified into the high unit group (range, 66-150 units), and 5 into the low unit group (36-60). Four patients in the high unit and 3 in the low unit groups showed diffuse iron deposition in the liver on DECT images. Two patients in the high unit and 1 in the low unit groups showed focal iron deposition in the left lobe of the liver. One patient in the low unit group did not show iron deposition.

[Conclusion]

Discrepancies between SF levels and DECT images indicate that DECT is a useful technique for the accurate evaluation of LIC, and the detection of focal iron deposition in the liver may be useful for optimizing iron chelation therapy.