RESUMO
To investigate the relationship of hepatic signal intensity and T2 with histologic grading in an animal model of oral iron overload and to determine the duration of feeding necessary to produce abnormalities detectable on magnetic resonance (MR) images, hepatic iron overload was induced in 12 rats by feeding them a diet supplemented with 4% carbonyl iron for 2-11 weeks. Iron overload seen on MR images was graded independently and blindly by two radiologists as normal, mild, moderate, or severe. The rats were killed, and histologic findings were graded blindly by four pathologists using a similar subjective scale. Hepatic T2 values were estimated from spin-echo images. In the rats with iron overload, intracellular iron deposition was noted on histologic studies. On MR images, hepatic signal intensity and T2 decreased after only 2 weeks of dietary iron overload, and both continued to decrease with longer duration of feeding. There was significant correlation between iron overload duration and changes on MR images and between MR images and histologic grading (r = .92, P = .0001 for both). The mean T2 of hepatic iron overload decreased with longer duration of feeding.
Assuntos
Hemocromatose/diagnóstico , Hepatopatias/diagnóstico , Fígado/patologia , Imageamento por Ressonância Magnética , Animais , Ferro/administração & dosagem , Ratos , Ratos Sprague-Dawley , Fatores de TempoRESUMO
Magnetic resonance (MR) imaging was performed in 14 patients with biopsy-proved polycythemia vera (n = 4) or myelofibrosis (n = 10) to determine whether MR imaging findings can be correlated with the clinicopathologic diagnosis and established clinical parameters of severity (serum lactate dehydrogenase [LDH] and cholesterol levels) and chronicity (spleen size). Evaluation of marrow in the proximal femurs showed that patients could be categorized into three distinct groups based on anatomic patterns of normal fatty and abnormal low-signal-intensity (non-fatty) marrow in the femoral capital epiphysis (FCE) and greater trochanter (GT). Patients with nonfatty marrow in both the FCE and GT (n = 8) had significantly higher serum LDH (P less than .02) and lower serum cholesterol (P less than .02) levels than patients with fatty marrow in at least the GT (n = 6). Splenic volume, as measured from MR images, was significantly greater in the myelofibrosis group than in the polycythemia vera group (P less than .001). MR imaging provided a better understanding of these hematologic disorders and novel parameters for classification that are different from conventional histologic and laboratory data.
Assuntos
Medula Óssea/patologia , Imageamento por Ressonância Magnética , Policitemia Vera/patologia , Mielofibrose Primária/patologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Colesterol/sangue , Feminino , Fêmur/patologia , Humanos , L-Lactato Desidrogenase/sangue , Vértebras Lombares/patologia , Masculino , Pessoa de Meia-Idade , Policitemia Vera/sangue , Mielofibrose Primária/sangue , Estudos Retrospectivos , Esplenomegalia/patologiaRESUMO
In an evaluation of safe, inexpensive, orally administered contrast agents for use at magnetic resonance imaging, different concentrations of the clay agents kaolin-pectate and attapulgite were compared in an in vitro phantom by performing spin-echo imaging with variable echo times to estimate T2 relaxation time. Additional phantoms containing from 0% to 100% attapulgite or barium preparations were compared by using spin-echo and spoiled-gradient-echo techniques to estimate T1, T2, and T2* relaxation times. In vivo spin-echo and gradient-echo images were obtained of 10 healthy volunteers and of five patients with pancreatic disease after oral administration of 12-16 oz of attapulgite preparation. T1 and T2 relaxation times obtained with use of attapulgite were slightly lower than those obtained with kaolin-pectate at both 50% and 25% concentrations. Compared with barium, attapulgite had shorter T1, T2, and T2* relaxation times, and concentration-dependent relaxivity was greater by nearly an order of magnitude. All subjects were able to drink the attapulgite, and the only complaints were of bad taste and mildly loose stools.
Assuntos
Sulfato de Bário , Meios de Contraste , Intestinos/anatomia & histologia , Caulim , Compostos de Magnésio , Imageamento por Ressonância Magnética , Pectinas , Compostos de Silício , Combinação de Medicamentos , Humanos , Aumento da Imagem , Magnésio , Modelos Estruturais , Silício , ViscosidadeRESUMO
Parenchymal iron deposition occurs in hemochromatosis, while iron is deposited in reticuloendothelial (RE) cells after blood transfusions or rhabdomyolysis. Magnetic resonance images of patients with decreased liver signal intensity on T2-weighted images at 1.5 T were blindly compared in an effort to distinguish these conditions. In each of five patients with hemochromatosis, the pancreas had low signal intensity, but splenic signal intensity was decreased in only one. In contrast, only three of the 16 patients with RE iron overload had low pancreatic signal intensity, while all of these patients either had low splenic signal intensity (n = 14) or previously underwent splenectomy (n = 2). Distinction among these causes of iron deposition is clinically important because parenchymal iron overload from hemochromatosis may produce significant tissue damage, while the RE iron of transfusions and rhabdomyolysis is of little clinical consequence.
Assuntos
Ferro/metabolismo , Células de Kupffer/metabolismo , Fígado/patologia , Imageamento por Ressonância Magnética , Adolescente , Adulto , Biópsia , Feminino , Hemocromatose/diagnóstico , Hemocromatose/etiologia , Hemocromatose/metabolismo , Humanos , Células de Kupffer/patologia , Fígado/metabolismo , Cirrose Hepática/diagnóstico , Cirrose Hepática/etiologia , Masculino , Pessoa de Meia-Idade , Pâncreas/metabolismo , Pâncreas/patologia , Estudos Retrospectivos , Baço/patologia , Reação TransfusionalRESUMO
Conventional "proton density" and "T2-weighted" spin-echo images are susceptible to motion induced artifact, which is exacerbated by lipid signals. Gradient moment nulling can reduce motion artifact but lengthens the minimum TE, degrading the "proton density" contrast. We designed a pulse sequence capable of optimizing proton density and T2-weighted contrast while suppressing lipid signals and motion induced artifacts. Proton density weighting was obtained by rapid readout gradient reversal immediately after the excitation RF pulse, within a conventional spin-echo sequence. By analyzing the behavior of the macroscopic magnetization and optimizing excitation flip angle, we suppressed T1 contribution to the image, thereby enhancing proton density and T2-weighted contrast with a two- to four-fold reduction of repetition time. This permitted an increased number of averages to be used, reducing motion induced artifacts. Fat suppression in the presence of motion was investigated in two groups of 8 volunteers each by (i) modified Dixon technique, (ii) selective excitation, and (iii) hybrid of both. Elimination of fat signal by the first technique was relatively uniform across the field of view, but it did not fully suppress the ghosts originating from fat motion. Selective excitation, while sensitive to the main field inhomogeneity, largely eliminated the ghosts (0.21 +/- 0.05 vs. 0.29 +/- 0.06, p less than 0.01). The hybrid of both techniques combined with bandwidth optimization, however, showed the best results (0.17 +/- 0.04, p less than 0.001). Variable flip-angle imaging allows optimization of image contrast which, along with averaging and effective fat suppression, significantly improves gradient- and spin-echo imaging, particularly in the presence of motion.
Assuntos
Tecido Adiposo , Lipídeos , Imageamento por Ressonância Magnética/métodos , Humanos , Aumento da Imagem , Fígado/anatomia & histologia , Prótons , Baço/anatomia & histologiaRESUMO
In MR imaging, the sampling bandwidth is the rate at which the signal is digitized by the analog-to-digital converter. Reducing the sampling bandwidth can decrease noise in long TE images at the expense of increases in the artifacts of chemical-shift misregistration and motion. We compared 39 pairs of axial images with bandwidths of 32 kHz and 8-10 kHz. In 23 of these comparison studies (six female pelvis, seven male pelvis, 10 abdomen), all other variables were held constant, and in 16 comparisons (10 female pelvis, six male pelvis), signal from fat was suppressed in images with reduced bandwidth. Six patients with 11 liver lesions were included in those undergoing abdominal imaging. In three patients, fat was suppressed in images of the abdomen. The contrast-to-noise ratio was greater with reduced bandwidth for urine vs fat (24.5 vs 17.2; p less than .05) and central vs peripheral parts of the prostate gland (34.1 vs 22.7; p less than .02). In the abdomen, the contrast-to-noise ratio was increased between liver and right kidney (36.6 vs 25.2; p less than .01) and between liver and lesion (30.2 vs 18.2; p less than .005), but the motion-induced artifact was worse. An increase in chemical-shift misregistration did not affect the appearance of the internal structure of the uterus, prostate gland, or liver, but it made examination of the ovaries, seminal vesicles, and extrahepatic tissues difficult. The chemical-shift artifact in pelvic images could be eliminated by suppressing signal from fat with frequency-selective saturation pulses, but results were less satisfactory in the abdomen. When reduced bandwidth and fat suppression were combined, the contrast-to-noise ratio was improved for endometrium vs myometrium (22.9 vs 15.2; p less than .05) and central vs peripheral parts of the prostate gland (62.7 vs 28.5; p less than .02). Reduction of the sampling bandwidth is a promising technique for imaging the pelvis with small field of view and long TR/TE, but it currently appears less promising for images in the upper abdomen at 1.5 T. The increased chemical-shift artifact caused by reduced bandwidth can be eliminated by suppressing signal from fat.
Assuntos
Abdome/anatomia & histologia , Imageamento por Ressonância Magnética , Pelve/anatomia & histologia , Tecido Adiposo/anatomia & histologia , Feminino , Humanos , Imageamento por Ressonância Magnética/métodos , MasculinoAssuntos
Adenocarcinoma Mucinoso/secundário , Neoplasias dos Genitais Masculinos/secundário , Escroto/patologia , Neoplasias do Colo Sigmoide , Ultrassonografia , Adenocarcinoma Mucinoso/diagnóstico , Idoso , Idoso de 80 Anos ou mais , Neoplasias dos Genitais Masculinos/diagnóstico , Humanos , MasculinoRESUMO
Dependence on T1 contrast can be reduced by changing the excitation flip angle. The authors compared T2-weighted spin-echo images (with 30 degrees and 90 degrees flip angles) of the male and female pelvis in 22 individuals. In six women imaged with a 1,000/80 sequence (repetition time msec/echo time msec), signal difference-to-noise ratios (SD/Ns) were higher with a 30 degree flip angle than with a 90 degree angle for urine/fat (mean, 15.2 vs -6.2; P less than .05) and endometrium/myometrium (13.8 vs 9.0, P less than .05). In eight additional examinations, a 1,000/80 sequence with a 30 degree flip angle and two signal averages had less motion artifact (1.2 vs 2.7, P less than .01) than a 2,000/80 sequence with a 90 degree angle and one signal average (4.5 minutes each); SD/Ns were similar. In a third series of experiments, contiguous sections without cross talk, obtained by interleaving two 1,000/100, 30 degrees-flip-angle acquisitions, had better contrast than contiguous sections obtained at 2,400/100 with a 90 degree flip angle (10 minutes each), with SD/Ns of urine/fat of 28.5 versus 16.1 (P less than .01) and SD/Ns of endometrium/myometrium of 15.5 versus 7.8 (P less than .05). Reducing the flip angle can improve examination time, contrast, or motion artifact suppression or eliminate cross talk in T2-weighted spin-echo MR imaging of the pelvis.
Assuntos
Doenças dos Genitais Femininos/diagnóstico , Doenças dos Genitais Masculinos/diagnóstico , Imageamento por Ressonância Magnética/métodos , Pelve/anatomia & histologia , Doenças Urológicas/diagnóstico , Feminino , Humanos , MasculinoRESUMO
Preoperative ultrasonography was used as an alternative to x-ray mammography to localize 92 breast lesions encountered in 82 patients. Recommendation for biopsy was made on the basis of the ultrasonographic finding of a nonpalpable mass or an area of architectural distortion, or in the presence of equivocal physical findings if sonomammography demonstrated a solid or an anechoic mass. Sonomammography was performed in the operating room, just before anticipated biopsy, with a hand-held high-resolution scanner. When the suspicious area was imaged and its precise location noted, the breast was then prepared and draped in the usual manner, and a biopsy was performed. If the suspicious area could not be easily localized after the incision was made and the breast explored, the transducer was "gowned" and used directly in the wound to help find the lesion. This technique has proven effective and accurate. In selected patients ultrasonography may be used as well as, or instead of, x-ray needle localization for the precise excision of nonpalpable breast lesions, excluding calcifications.