Hyperpolarized Nuclei for NMR Imaging and Spectroscopy - Lunds ...

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2 Background 2.1 NMR physics 2.1.1 The nuclear spin A fundamental property of the atomic nucleus is the nuclear spin, described by the spin quantum number I. Strictly speaking, the nuclear spin is a purely quantum mechanical quantity, but in terms of classical physics it may be pictured as an angular momentum — the nucleus rotates around its axis. Many atomic nuclei (mainly those with an odd mass number) have a nonzero spin quantum number and can be studied with NMR, e.g., 1 H, 3 He, and 13 C. Nuclei having the spin quantum number I = 0 “do not rotate” and cannot be studied with NMR. Most nuclei with an even mass number, e.g., 4 He and 12 C belong to this latter group. Due to its positive charge, a rotating nucleus constitutes a microscopic ring current, giving rise to a microscopic magnetic moment µµµµ, which can be pictured as a microscopic compass needle. † When placed in an external magnetic field B 0, the magnetic moments orient themselves along the magnetic field; but as opposed to compass needles, only discrete orientations are allowed. The number of allowed orientations is given by 2I+1, and each orientation is associated with a distinct quantum energy E m: 4 Em =−µµ ⋅ B0 = mγh B0 [1] where m =−I, −I+1, … , +I is the magnetic quantum number, and the constant γ is called the “gyromagnetic ratio,” characteristic of each atomic nucleus. The magnetic moment µµµµ cannot be oriented parallel to B 0, and will thus experience a torque trying to align µµµµ with B 0. In analogy with a top rotating in the earth’s gravity field, this torque will cause µµµµ to revolve around B 0 with an angular frequency ω, denoted the Larmor frequency: ω = γB0. [2] The nuclei investigated in this thesis ( 3 He, 13 C, and 129 Xe) all have the spin quantum number I = 1 2 , and thus two orientations are possible: namely, parallel to B0 (“spin up”) and anti-parallel to B0 (“spin down”). By † Bold typeface denotes vectors.
vector addition of all the magnetic moments, oriented in either the “up” or the “down” direction, a macroscopic magnetization vector parallel to B 0 is obtained: ∑ ∑ M = µµ + µµ up down . [3] However, this magnetization cannot be observed unless a rotating, transverse component is created. Such a component is created by tilting, or “flipping,” M sideways, which in turn is accomplished by applying a second magnetic field, B 1, perpendicular to B 0, and oscillating with the Larmor frequency. The angle at which the B 1 field tilts M is called the “flip angle.” When a sample is placed near or inside a receiver coil in the magnetic field, the transverse magnetization component (rotating with Larmor frequency) will induce a voltage across the terminals of the receiver coil with an amplitude proportional to the magnitude of M. 2.1.2 Nuclear polarization The number of nuclei populating each energy state may be denoted N up and N down, respectively. If the two populations are equal, their magnetic moments cancel, resulting in zero macroscopic magnetization, and thus no NMR signal. Due to the slightly higher energy associated with the “down” direction, the number of nuclei pointing “down” will, however, be slightly fewer than the number of nuclei pointing “up” (N down < N up) under thermal equilibrium conditions (see Figure 1). The nuclear polarization P (for nuclei with the spin quantum number I = 1 2 ) is defined by N − N P ≡ N + N up down up down . [4] The magnetization M, and thus the NMR signal, S, will be proportional to the polarization and the total number of nuclei within the sample (N 0 = N up + N down): S ∝ N0 P. [5] The populations of the energy levels are, under thermal equilibrium conditions, governed by the Boltzmann distribution 5
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Page 4 and 5: DOKUMENTDATABLAD enl SIS 61 41 21 O
Page 6 and 7: Doctoral Dissertation Department of
Page 9 and 10: Abstract Based on the principle of
Page 11 and 12: Original papers This thesis is base
Page 13 and 14: Table of Contents 1 Introduction .
Page 15 and 16: 1 Introduction The phenomenon of nu
Page 17: By using hyperpolarized imaging age
Page 21 and 22: illustrates the difference between
Page 23 and 24: pumping process (Colegrove and Fran
Page 25 and 26: thetic effects, and has been used a
Page 27 and 28: 1 T 1,O2 p = ξ O2 [11] where ξ Xe
Page 29 and 30: 1 2 2 −6 ∝ γC γHrτ c. [17] T
Page 31 and 32: and thus breaks down at very low fr
Page 33 and 34: 230 mT, e.g., Tseng et al. 1998, Du
Page 35 and 36: lation-perfusion ratio (V · A/Q ·
Page 37 and 38: after gas inhalation, due to the wa
Page 39 and 40: tion of an NMR signal from a small
Page 41 and 42: larized gas with air took place as
Page 43 and 44: Table 5. Parameters of the imaging
Page 45 and 46: The images were evaluated with resp
Page 47 and 48: partial pressure present within the
Page 49 and 50: 3.8.2 Measurement procedure The spe
Page 51 and 52: 4.2 Vascular imaging of a 13 C-base
Page 53 and 54: gions. In central lung areas, regio
Page 55 and 56: 4.5 Diffusion capacity and perfusio
Page 57 and 58: 5 Discussion In this thesis, three
Page 59 and 60: due to the increased demand on the
Page 61 and 62: 5.3 Hyperpolarized 3 He ventilation
Page 63 and 64: a theoretical T 1 of ∼38 min in t
Page 65 and 66: eath-holding periods during, e.g.,
Page 67 and 68: 6 Conclusions The phantom study in
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8 References ABRAGAM A, GOLDMAN M.
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CHEN XJ, MÖLLER HE, CHAWLA MS, COF
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GIERADA DS, SAAM B, YABLONSKIY D, C
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KAUCZOR HU, HANKE A, VAN BEEK EJ. A
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OLSSON LE, MAGNUSSON P, DENINGER AJ
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TILTON RF, JR., KUNTZ ID, JR. Nucle
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Paper I
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formance of the gradient system, si
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S. MÅNSSON ET AL. Fig. 2. a-h) EPI
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though several technical issues rem
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Hyperpolarized 13 C MR angiography
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Introduction The most widespread te
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of the gradient moments prior to ea
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Methods Polarization procedure The
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secutive trueFISP images were acqui
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also to several other sources such
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low γ of 13 C reduces the sensitiv
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9. Chawla MS, Chen XJ, Möller HE,
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My 1 0.8 0.6 0.4 0.2 0 0 50 100 150
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Signal [a.u] 100 90 80 70 60 50 40
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a b Figure 5. Series of angiograms
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Paper III
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224 Deninger et al. FIG. 1. Sketch
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226 Deninger et al. FIG. 2. Coronal
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228 Deninger et al. FIG. 6. Histogr
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230 Deninger et al. FIG. 9. Monte C
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232 Deninger et al. 5. Gur D, Draye
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3 He MRI-based measurement of posit
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Introduction It is well known that
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3 He imaging All experiments were p
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coefficients b 1 and b 2, respectiv
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Using VI data after subtraction of
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To investigate whether the calculat
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14. Gur D, Drayer BP, Borovetz HS,
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Table 1. Gradient of VI [cm −1 ]
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Cycle 1 Cycle 2 Cycle 3 Cycle 4 2 s
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a Prone Ventilation index c Supine
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a Prone Supine 0 b 1 R 2 Prone Supi
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Paper V
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Abstract The ability to quantify pu
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lation and perfusion information by
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Applying the conditions at the inne
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where L is obtained from Eq. [8]. V
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After tracheal intubation, the anim
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Parametric analysis The fit of the
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in the LPS-treated group is consist
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3. Worsley DF, Palevsky HI, Alavi A
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enin activity in rats chronically e
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V-20 blood without Xe C a V a (t) L
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V-22 Error in estimated diffusion l
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V-24 NMR Ventilator repetition loop
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Figure 7. The peak amplitudes (circ
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