Susceptibility effects due to the presence of hemorrhage have been observed in a substantial number of patients and are a potential source of artifact in in vivo spectroscopy. The studies so far have ...concentrated on observations of phase differences, but amplitude variations also exist. This article reviews the degree to which the two are independent and suggests that at least three different pulse sequences are necessary to characterize effects due to local field inhomogeneities arising in clinical studies.
Recent developments in MRI of the brain are reviewed. Over the past year there has been a general improvement in image quality, a paramagnetic contrast agent has been used in clinical practice, and ...surface coils have been used more generally in imaging. A wider range of disease has been studied, and there has been considerable agreement about the advantages and disadvantages of MRI at a basic level. As the technique moves into routine clinical use, questions about the economics of the technique are becoming more pressing.
Attention is drawn to the variation in the computed tomography (CT) attenuation value of water with temperature. A difference of 5 to 6 Hounsfield units (1,000 scale) between typical room and body ...temperatures can be predicted as a consequence of the change in the density of water and was confirmed experimentally. This difference may be of significance in the calibration of CT machines, in the determination of "absolute" CT attenuation values for body tissues and fluids, and in comparing tissue attenuation values obtained in vivo and in vitro.
In vivo attenuation values of 19 fluid collections in 17 patients were compared with in vitro values obtained on examination of the aspirated fluids within the calibration phantom of an EMI CT5005 ...body scanner. While the in vitro values showed a 5.2 Hounsfield unit (HU:1,000 scale). difference between cysts and abscesses, spectral errors of up to 28.6 HU were sufficiently large for this distinction to be lost in vivo. Good correlation was found between ascitic fluid protein concentration and in vitro attenuation values, but not with in vivo values. An experimental reconstruction program appeared to give more accurate in vivo results than the standard commercial algorithm. A water control showed errors of similar magnitude to those with the fluid collections and did not provide any simple correction for the errors in the fluid attenuation values. Similar results were found for urine examined in vitro and in vivo. The administration of intravenous contrast agents tended to elevate in vivo fluid attenuation values, but refrigeration for 6 months produced little change in in vitro values.
We observe linewidths of 0.1-0.4 ppm in 31P spectra of human muscle, liver, and brain. T2 measurements of muscle phosphocreatine, together with previous brain studies, indicate that further ...improvements in linewidth to 0.02-0.05 ppm might often be achieved, but in some lesions magnetic susceptibility variations may limit spectral resolution.
A prospective magnetic resonance imaging (MRI) study was carried out in 13 patients (19 examinations) with primary bone tumours to assess the relative value of each of four pulse sequences in showing ...the extent and nature of the lesion. The four pulse sequences used were a T1-weighted spin-echo (SE544/44), a T2-weighted spin echo (SE1500/80), a short TI inversion recovery (STIR) (IR500/100/44), and a partial saturation (PS) (PS500/22) with field echo data collection. For soft tissue disease the combination of PS and STIR gave better definition of the boundary of the tumour than the more conventional T1 and T2-weighted spin echo sequences. For the demonstration of bone cortex, periosteal change and calcification, T1 and T2-weighted spin echo sequences were better. However, for calcified tissues, plain radiographs were better than either MRI combination. On the assumption that plain films will be available in all cases, PS and STIR sequences could therefore be substituted for T1 and T2-weighted spin echo sequences allowing an increase in soft tissue detectability for lesions in both red and yellow marrow.
The CT features in 30 cases of suspected intra-abdominal abscesses are reviewed. The cases were grouped into proven (24), probable (4), and possible (2) abscess on clinical grounds, and were analyzed ...according to site within the abdomen. Two cases of carcinoma with fluid collections mimicking abscesses are also discussed. In the appropriate clinical context, abdominal abscess is identified on CT as a circumscribed low-density region within the abdomen. Subphrenic, hepatic, and splenic abscesses were readily recognized without contrast enhancement inthe majority of cases, although contrast enhancement consistently rendered loculation within hepatic abscesses more obvious. Aspiration and drainage under CT control were invaluable in diagnosis, permitting the identification of the causative organism in 18 cases. The precise anatomical detail provided by CT was important in achieving successful catheter placement for drainage.
Advanced MR imaging techniques Salonen, David; Bradley, William G; Bydder, Graeme M
Canadian Association of Radiologists Journal,
06/1998, Letnik:
49, Številka:
3
Book Review
Recenzirano
By this point, the editors have set the tone of the book. It is not for the casual reader, but for the reader who is looking for a strong understanding of advanced MRI. The next 2 parts look at ...contrast mechanisms in inversion recovery sequences and functional MRI, as well as contrast agents and registration/subtraction of serial MR images. The last 5 chapters address a range of topics, including interventional MRI, proton spectroscopy and magnetoencephalography.
In 1996 we reported sequential magnetic resonance imaging study in an infant with merosin-deficient congenital muscular dystrophy with normal brain magnetic resonance imaging at 3 weeks and white ...matter changes by 6 months. We now report an infant with merosin-deficient congenital muscular dystrophy with a mild degree of white matter changes already present on brain magnetic resonance imaging at 5 days of age. The difference may be due to a difference in the T2 sequences used. The images in this present case were obtained with a fast spin echo sequence (echo time: 210 ms). The increased T2 weighted may be responsible for a better detection of the white matter changes at an early stage, when they can be missed on conventional, less weighting T2 sequences. These results suggest that, by using appropriate sequences, mild white matter changes may be detectable on brain magnetic resonance imaging in the first days of life in infants with merosin-deficient congenital muscular dystrophy.
