Cellular Lactate Spectroscopy Using 1.5 Tesla Clinical Apparatus

Abstract

Cellular lactate is a key cellular metabolite and marker of anaerobic glycolysis. Cellular lactate uptake, release, production from glucose and glycogen, and interconversion with pyruvate are important determinants of cellular energy. It is known that lactate is present in the spectrum of neoplasms and low malignancy (without necrotic lesions). Also, the appearance of lactate signals is associated with anaerobic glucose, mitochondrial dysfunction, and other inflammatory responses. The aim of this study was the detection of lactate in cell cultures with the use of proton magnetic resonance (¹H MRS) and a 1.5 Tesla clinical apparatus (MR OPTIMA 360), characterized as a medium-field system. In this study, selected metabolites, together with cellular lactate, were identified with the use of an appropriate protocol and management algorithm. This paper describes the results obtained for cancer cell cultures. This medium-field system has proven the possibility of detecting small molecules, such as lactate, with clinical instruments. ¹H MRS performed using clinical MR apparatus is a useful tool for clinical analysis.

Keywords: 1.5 Tesla field; lactate; magnetic resonance spectroscopy.

Figure 1

Lactate (Figure 1) has two resonances in the ¹H spectrum: the first (β) at δ = 1.30 ppm, and the second (α) at δ = 4.08 ppm. The doublet is the result of the interaction of lactate proton peaks with the J-coupling (7 Hz). The second resonance (α) is a 1:3:3:1 quartet. The signal for TE = 144 ms is below the baseline, while for TE = 288 ms, it is above this line.

Figure 2

Evolution of the lactate signal as a function of TE time. The characteristic lactate peaks were around 1.3–1.4 ppm (own elaboration).

Figure 3

Lactic acid. (a) The spectrum presented in the upper part of the image was made for the echo time TE = 288 ms, NEX = 128, total number of scans: 128, sequence name: PROBE-P, (b) while for the lower spectrum: TE = 144 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P. The test performed with the experimental coil is shown in Figure 2. Voxel size: 8 × 8 × 8 mm (own elaboration).

Figure 4

The results for scanning the culture medium, RPMI1640, using the 1.5 T system GEMS type Optima 360 MR, TE = 28, TR = 1500 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P. Voxel size: 8 × 8 × 8 mm (own elaboration).

Figure 5

Glucose test (2 mL H₂O + 50 mg Glucose).

Figure 6

A549 cell culture spectroscopy, performed using the Optima 360MR clinical system, prod. GEMS. (a) TE = 28, TR = 4000 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P, (b) TE = 144, TR = 4000 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P, (c) TE = 35 ms, TR = 6000 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P, (d) TE = 288 ms, TR = 6000 ms, NEX = 8, total number of scans: 128, voxel size for all spectra: 8 × 8 × 8 mm (own elaboration).

Figure 7

A549 cell culture spectroscopy, performed on the Optima clinical system prod. GEHC, (a) spectrum in Power mode TE = 144 ms, TR = 4000 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P, (b) component of the Real spectrum TE = 288 ms, TR = 4000 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P, (c) component of the Real spectrum TE = 144 ms, TR = 4000 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P. Voxel size for all spectra: 8 × 8 × 8 mm (own elaboration).

Figure 8

The appearance of the L1 inductor of the receiving coil.

Figure 9

Spectroscopy of the CRL2314 cell culture with marked locations for the lactate peaks, (a) spectrum in Power mode TE = 144, TR = 4000 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P, (b) component of the Real spectrum TE = 288 ms, TR = 4000 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P, (c) component of the Real spectrum TE = 144 ms, TR = 4000 ms, NEX = 8, total number of scans: 128, sequence name: PROBE-P. The test performed with the experimental coil shown in Figure 2. Voxel size for all spectra: 8 × 8 × 8 mm (own study).

Figure 10

PRESS sequence diagram. RF- signal, with resonance frequency, Gx, Gy, Gz—gradient pulses in the X, Y, Z axes, 90°, 180°—pulse inverting the magnetization vector by an angle of 90° and 180°, respectively, PRESS ECHO—recorded signal, TE—echo time.

Figure 11

STEAM sequence diagram. RF- resonant frequency signal, Gx, Gy, Gz—gradient pulses in the X, Y, Z axes, 90°—pulse inverting the magnetization vector by an angle of 90°, STIMULATED ECHO—recorded signal, TE—echo time, TM—mixing time.

Figure 12

(a). Diagram of the receiving part of the coil, (b) arrangement of solder pads on the PCB, (c) receiving coil frequency response.

Figure 13

The appearance of the assembled receiver. L1, L2, L3—induction coil, C1, C2, C3—capacitor, J1—MCX connector (own elaboration).