Imaging discordance between hepatic angiography versus Tc-99m-MAA SPECT/CT: a case series, technical discussion and clinical implications

Abstract

During pre-therapy evaluation for yttrium-90 (Y-90) radioembolization, it is uncommon to find severe imaging discordance between hepatic angiography versus technetium-99m-macroaggregated albumin (Tc-99m-MAA) single photon emission computed tomography with integrated low-dose CT (SPECT/CT). The reasons for severe imaging discordance are unclear, and literature is scarce. We describe 3 patients with severe imaging discordance, whereby tumor angiographic contrast hypervascularity was markedly mismatched to the corresponding Tc-99m-MAA SPECT/CT, and its clinical impact. The incidence of severe imaging discordance at our institution was 4% (3 of 74 cases). We postulate that imaging discordance could be due to a combination of 3 factors: (1) different injection rates between soluble contrast molecules versus Tc-99m-MAA; (2) different arterial flow hemodynamics between soluble contrast molecules versus Tc-99m-MAA; (3) eccentric release position of Tc-99m-MAA due to microcatheter tip location, inadvertently selecting non-target microparticle trajectories. Tc-99m-MAA SPECT/CT more accurately represents hepatic microparticle biodistribution than soluble contrast hepatic angiography and should be a key criterion in patient selection for Y-90 radioembolization. Tc-99m-MAA SPECT/CT provides more information than planar scintigraphy to guide radiation planning and clinical decision making. Severe imaging discordance at pre-therapy evaluation is ominous and should be followed up by changes to the final vascular approach during Y-90 radioembolization.

Systematic Evaluation of Tumoral 99mTc-MAA Uptake Using SPECT and SPECT/CT in 502 Patients Before 90Y Radioembolization

“…Significant differences between vascularization of tumors as assessed during angiography and 99m Tc-MAA uptake on SPECT are described. Therefore, conclusions derived from contrast enhancement of tumors have to be drawn with caution, especially as results derived from angiography and cross-sectional imaging are contradictory in some cases (13,14).…”

A review of 3D image-based dosimetry, technical considerations and emerging perspectives in 90Y microsphere therapy

“…Other work shows a sensitivity of 100% of using SPECT-CT to detect extrahepatic uptake compared to 41% for non attenuation corrected SPECT and 32% for planar imaging respectively [22]. Recently evaluated also is the discordance between hepatic angiography and MAA SPECT, noting severe discordance in only 3 of 74 cases of patients with HCC [23].…”

“…However, different physical properties, surgical procedures and timing between catheterizations result in MAA being an imperfect surrogate for GMS and RMS [23,71,72]. Recent discussions observe that discordance in MAA-microsphere distribution may be attributable to the differing vascularity of HCC and metastases [59], with a suggestion of a more concordant relationship in HCC cases [73].…”

“…Surgical procedures have been identified as a cause of MAA-MS mismatch such as differences in injection rates, microcatheter positioning [75] and arterial flow hemodynamics [23]. A 5-10 mm difference in catheter position between tip and artery opening has been shown to have a major impact on microsphere flow distribution [58,77].…”

Multiagent imaging of liver tumors with reference to intra-arterial radioembolization

“…A discrepancy between the distribution of 99m Tc-MAA in the liver and the vascular territory to be treated may occur in a small percentage (\4 %) of cases and can be explained by different injection rates and different arterial flow between soluble contrast molecules versus 99m Tc-MAA, or to different locations of the microcatheter tip between the diagnostic phase and the treatment phase. Kao and colleagues [30] showed that 99m Tc-MAA SPECT/CT more accurately represents hepatic microparticle biodistribution than does soluble contrast hepatic angiography. Alternatively, the tumor may have an unidentified accessory arterial blood supply or may have caused vascular remodeling of the local arteries.…”