Thermoacoustic imaging (TAI) is a promising new modality that shows potential for improved detection of small more easily treatable breast tumors. In TAI, an incident microwave pulse is locally absorbed, causing thermoelastic expansion and the generation of ultrasonic waves, which are detected to form an image proportional to the sample's absorption. This study explores the use of spectroscopic TAI used in conjunction with contrast agents, to increase the modality's diagnostic capabilities. The absorption magnitude and spectral properties of metallic and semiconducting single-walled carbon nanotubes (SWNT) are investigated. At 2.9 GHz both types of nanoparticles were found to generate ∼40% greater TA signal than water. The TA signal of each SWNT type was highly linearly correlated with nanoparticle concentration (R2 ≥ 0.98; p < 0.01). Furthermore, between 7 and 9 GHz, semiconducting and metallic SWNTs both exhibited strong positive absorption slopes of 1.75 AU/GHz and 2.8 AU/GHz, respectively, and relative to water. The absorption spectra of SWNTs could potentially be used to help discriminate them from healthy adipose tissue, enabling highly specific and contrast enhanced detection of small breast tumors.