Figure 1. ISIS-localized ³¹P MR spectrum, obtained at 4.7 T from MCF-7 human breast cancer xenograft growing in the mammary fat pad of a SCID mouse. Spectral volume was 1 cm³ and acquisition time was 30 min. Abbreviations: 3-APP, 3-aminopropylphosphonate; PEtn, phosphoethanolamine; PCho, phosphocholine; P_i, inorganic phosphate; GPC, glycerophosphorylcholine; PCr, phosphocreatine; -,-,- NTP, terminal, primary and middle phosphates of nucleoside triphosphates (e.g. GTP, ATP). Prior to spectroscopy, the mouse was injected with 3-APP, a nontoxic extracellular pH marker. Intra- and extracellular pH values are determined from the chemical shifts of P_i and 3-APP, respectively.

Figure 2. Images of a 12-mm-thick axial section using identical fields-of-view from a human patient, acquired at a field strength of 1.5 T. (a) Conventional T₂-weighted fast spin echo MRI. (b) Conventional postcontrast T₁-weighted MRI. (c) Map of choline intensities. (d) Image of the apparent water diffusion coefficient. The spectroscopic image (c) was acquired with a repetition time of 2.3 s and an echo time of 272 ms, and is shown at the nominal volume resolution (10 × 10 × 12 mm) without smoothing. Courtesy of J.R. Alger, Department of Radiology, UCLA.

Figure 3. ¹⁹F spectra from tumours of HT-29 human colon cancer cells growing in Nude mice treated with 5-fluorocytosine. Spectrum (a) was obtained from tumours of control HT-29neo cells. Spectrum (b) was obtained from tumours of HT-29 cells transfected with the cytidyltransferase gene from Saccharomyces cerevisiae. Surface coillocalized spectra were obtained from volumes of approximately 1 cm × 1 cm × 1 cm in an acquisition time of 12 min. Abbreviations: 5-FC, 5-fluorocytosine; 5-FU, 5-fluorouracil; FNuc, fluorinated nucleotides; FAl, fluoro--d-alanine. Reprinted with permission from Stegman LD, Rehemtulla A, Beattie B et al. (1999) Noninvasive quantitation of cytosine deaminase transgene expression in human tumor xenografts with in vivo magnetic resonance spectroscopy. Proceedings of the National Academy of Sciences of the USA 96: 9821–9826.