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; γ‐,α‐,β‐ 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.

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.

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; FβAl, fluoro‐β‐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.