We describe the use of two-dimensional ultrashort echo time (2D UTE) sequences with minimum TEs of 8
μs to image and quantify cortical bone on a clinical 3T scanner. An adiabatic inversion pulse was ...used for long
T
2 water and fat signal suppression. Adiabatic inversion prepared UTE acquisitions with varying TEs were used for
T
2
∗
measurement. Saturation recovery UTE acquisitions were used for
T
1 measurement. Bone water concentration was measured with the aid of an external reference phantom. UTE techniques were evaluated on cadaveric specimens and healthy volunteers. A signal-to-noise ratio of around 30, contrast-to-noise ratio of around 27/20 between bone and muscle/fat were achieved in tibia in vivo with a nominal voxel size of 0.23
×
0.23
×
6.0 mm
3 in a scan time of 5
min. A mean
T
1 of 223
±
11
ms and mean
T
2
∗
of 390
±
19
μs were found. Mean bone water concentrations of 23.3
±
1.6% with UTE and 21.7
±
1.3% with adiabatic inversion prepared UTE sequences were found in tibia in five normal volunteers. The results show that in vivo qualitative and quantitative evaluation of cortical bone is feasible with 2D UTE sequences.
To test the hypothesis that intensity modulated radiation therapy (IMRT) can reduce radiation dose to functional bone marrow (BM) in patients with pelvic malignancies (phase IA) and estimate the ...clinical feasibility and acute toxicity associated with this technique (phase IB).
We enrolled 31 subjects (19 with gynecologic cancer and 12 with anal cancer) in an institutional review board-approved prospective trial (6 in the pilot study, 10 in phase IA, and 15 in phase IB). The mean age was 52 years; 8 of 31 patients (26%) were men. Twenty-one subjects completed (18)F-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) simulation and magnetic resonance imaging by use of quantitative IDEAL (IDEAL IQ; GE Healthcare, Waukesha, WI). The PET/CT and IDEAL IQ were registered, and BM subvolumes were segmented above the mean standardized uptake value and below the mean fat fraction within the pelvis and lumbar spine; their intersection was designated as functional BM for IMRT planning. Functional BM-sparing vs total BM-sparing IMRT plans were compared in 12 subjects; 10 were treated with functional BM-sparing pelvic IMRT per protocol.
In gynecologic cancer patients, the mean functional BM V(10) (volume receiving ≥10 Gy) and V(20) (volume receiving ≥20 Gy) were 85% vs 94% (P<.0001) and 70% vs 82% (P<.0001), respectively, for functional BM-sparing IMRT vs total BM-sparing IMRT. In anal cancer patients, the corresponding values were 75% vs 77% (P=.06) and 62% vs 67% (P=.002), respectively. Of 10 subjects treated with functional BM-sparing pelvic IMRT, 3 (30%) had acute grade 3 hematologic toxicity or greater.
IMRT can reduce dose to BM subregions identified by (18)F-fluorodeoxyglucose-PET/CT and IDEAL IQ. The efficacy of BM-sparing IMRT is being tested in a phase II trial.
Purpose
Using ultrashort echo time (UTE) MRI, we determined prevalence of abnormal cartilaginous endplate (CEP), and the relationship between CEP and disc degeneration in human lumbar spines.
...Materials and methods
Lumbar spines from 71 cadavers (age 14–74 years) were imaged at 3 T using sagittal UTE and spin echo T2 map sequences. On UTE images, CEP morphology was defined as “normal” with linear high signal intensity or “abnormal” with focal signal loss and/or irregularity. On spin echo images, disc grade and T2 values of the nucleus pulposus (NP) and annulus fibrosus (AF) were determined. 547 CEPs and 284 discs were analysed. Effects of age, sex, and level on CEP morphology, disc grade, and T2 values were determined. Effects of CEP abnormality on disc grade, T2 of NP, and T2 of AF were also determined.
Results
Overall prevalence of CEP abnormality was 33% and it tended to increase with older ages (p = 0.08) and at lower spinal levels of L5 than L2 or L3 (p = 0.001). Disc grades were higher and T2 values of the NP were lower in older spines (p < 0.001) and at lower disc level of L4-5 (p < 0.05). We found significant association between CEP and disc degeneration; discs adjacent to abnormal CEPs had high grades (p < 0.01) and lower T2 values of the NP (p < 0.05).
Conclusion
These results suggest that abnormal CEPs are frequently found, and it associates significantly with disc degeneration, suggesting an insight into pathoetiology of disc degeneration.
Clinical magnetic resonance imaging of multiple sclerosis (MS) has focused on indirect imaging of myelin in white matter by detecting signal from protons in the water associated with myelin. Here we ...show that protons in myelin can be directly imaged using ultrashort echo time (UTE) free induction decay (FID) and imaging sequences on a clinical 3T MR scanner. An adiabatic inversion recovery UTE (IR-UTE) sequence was used to detect signal from myelin and simultaneously suppress signal from water protons. Validation studies were performed on myelin lipid and myelin basic protein (MBP) phantoms in the forms of lyophilized powders as well as suspensions in D2O and H2O. IR-UTE sequences were then used to image MS brain specimens, healthy volunteers, and patients. The T2* of myelin was measured using a UTE FID sequence, as well as UTE and IR-UTE sequences at different TEs. T2* values of ~110–330μs were measured with UTE FID, as well as with UTE and IR-UTE sequences for myelin powders, myelin-D2O and myelin-H2O phantoms, consistent with selective imaging of myelin protons with IR-UTE sequences. Our studies showed myelin selective imaging of white matter in the brains in vitro and in vivo. Complete or partial signal loss was observed in specimens in areas of the brain with histopathologic evidence of myelin loss, and in the brain of patients with MS.
Clinical PD-FSE (A), T2-FSE (B) and FLAIR (C) imaging as well as IR-UTE (D) imaging of a brain specimen from a 28year old female donor with confirmed MS. MS lesions are hyperintense (thin arrows, A, B) on the PD-FSE and T2-FSE images, and hypointense (thin arrows, C) on the FLAIR image, and show signal loss on the IR-UTE image (thin arrows, D). Complete myelin loss is obvious in regions indicated by the thin arrows. Partial loss of signal is seen in the IR-UTE image (thick arrow, D) where the PD-FSE, T2-FSE and FLAIR images appear normal (thick arrows, A–C). Display omitted
•Myelin lipid and MBP phantoms are visible with UTE and IR-UTE imaging sequences.•Complete or partial myelin loss is observed in specimens with histopathologic confirmation.•Direct imaging of myelin in healthy volunteers and MS patients is investigated.•Obvious myelin loss can be observed in MS patients with the IR-UTE sequence.
The background underpinning the clinical use of ultrashort echo-time (UTE) pulse sequences for imaging tissues or tissue components with short T2s is reviewed. Tissues properties are discussed, and ...tissues are divided into those with a majority of short T2 relaxation components and those with a minority. Features of the basic physics relevant to UTE imaging are described including the fact that when the radiofrequency pulse duration is of the order T2, rotation of tissue magnetization into the transverse plane is incomplete. Consequences of the broad line-width of short T2 components are also discussed including their partial saturation by off-resonance fat suppression pulses as well as multislice and multiecho imaging. The need for rapid data acquisition of the order T2 is explained. The basic UTE pulse sequence with its half excitation pulse and radial imaging from the center of k-space is described together with options that suppress fat and/or long T2 components. Image interpretation is discussed. Clinical features of the imaging of cortical bone, tendons, ligaments, menisci, and periosteum as well as brain, liver, and spine are illustrated. Short T2 components in all of these tissues may show high signals. Possible future developments are outlined as are technical limitations.
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