Flame spectrometric analysis.
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History, 19th Century↗
Biomedical subjects
D G Mitchell
Publications and source records attributed to D G Mitchell.
Superficial masses with color flow Doppler imaging.
Color Doppler imaging findings and spectral waveforms were reviewed for 21 superficial masses in which color Doppler imaging revealed flow. This series included 5 benign hyperplastic lymph nodes, 5 malignant masses, 2 staphylococcus abscesses, and 9 pseudoaneurysms. Benign hyperplastic nodes had a vascular pattern consisting of prominent central flow with a branching radial pattern, reflecting the morphology of lymph nodes. One metastasis from melanoma demonstrated abundant peripheral flow and central avascularity, while the other 4 malignant masses and the 2 abscesses had sparse internal flow. All pseudoaneurysms had a to-and-fro imaging and spectral pattern (into the mass during systole, out during diastole), and/or a swirling pattern on real-time images (8 of 9 each). Doppler spectral analysis revealed continuous forward flow during diastole for all other masses and abscesses. Waveforms appeared similar for benign and malignant masses, and for abscesses. Conventional image-directed Doppler examinations performed prior to color Doppler studies failed to reveal flow in 2 partially thrombosed pseudoaneurysms, 1 malignant mass, and 1 abscess. Benign hyperplastic nodes, malignant masses, and pseudoaneurysms had distinctive color Doppler image appearances in this series, although demonstration of flow within a mass does not eliminate the possibility of abscess. Proper use of color and spectral Doppler analysis of superficial masses involves more than mere detection or exclusion of flow.
Abscess↗
MR imaging of shoulder injuries in professional baseball players.
Magnetic resonance (MR) imaging was used to evaluate the shoulders of 10 symptomatic professional baseball players and one asymptomatic player, with surgical correlation in six cases and arthrographic correlation in two cases. Seven small rotator cuff tears measuring 0.5-1 cm were identified on MR images, with arthrographic and surgical confirmation of these findings in two patients and surgical confirmation only in three patients. Cortical irregularity and/or subchondral cyst formation at the posterior aspect of the greater tuberosity near the insertion site of the infraspinatus tendon was found in five of the seven players with rotator cuff tears. Similar findings were noted in the asymptomatic volunteer and in one of the three players without cuff tear, who also had irregular thickening of the posterior capsule. These findings are believed to represent chronic avulsive changes resulting from the deceleration stresses of the follow-through motion.
Adult↗
Color flow-encoded MR imaging.
Magnetic resonance phase images can enable identification of any type of motion, including the velocity and direction of flow, and thus provide valuable supplements to magnitude images, which depict stationary tissue most effectively. A method is described for the simultaneous display of phase and magnitude by color encoding the phase data and superimposing it on the magnitude image to facilitate clinical interpretation. Color-encoded data not only depict the location and direction of flow along specific axes but can also provide relative velocity information through shades of color. Implementation of the technique is described, and the factors to be considered during interpretation of color flow-encoded images are discussed.
Aorta↗
Chemical shift artifact along the section-select axis.
Chemical shift artifact (CSA), familiar to radiologists along the frequency-encoding axis, also occurs along the section-select axis. The authors observed a case in which CSA mimicked a renal mass. Subsequent retrospective analysis of 50 abdominal magnetic resonance (MR) imaging studies was performed to assess occurrence of CSA adjacent to the upper and lower renal poles. CSA along the section-select axis was observed in 76% of cases and adjacent to 39% of all renal poles imaged. CSA along the section-select axis is common in abdominal MR imaging and may occasionally mimic disease.
Abdomen↗
MR imaging of hepatic iron overload in rat.
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.
Animals↗
Cirrhosis: multiobserver analysis of hepatic MR imaging findings in a heterogeneous population.
To investigate the magnetic resonance (MR) imaging findings of hepatic cirrhosis and the potential of MR imaging in differentiating cirrhosis from other hepatic abnormalities, three observers with different levels of expertise in MR imaging (specialist, experienced radiologist, and novice with special training) reviewed hepatic MR imaging examinations of 52 patients with biopsy-proved presence (n = 29) or absence (n = 23) of cirrhosis. All examinations included motion-compensated T1-weighted, T2-weighted, and flow-sensitive gradient-echo images. For all three observers, linear signal irregularity was more accurate than other findings. For the final diagnosis of cirrhosis, the specialist was most sensitive (76% at high threshold, 97% at low threshold), followed by the novice with special training (31% and 79%, respectively). Specificity was 100% for all observers at high threshold and 78%, 96%, and 87% for expert, experienced, and trained novice observers, respectively, at low threshold. Sensitivity did not vary regardless of severity of fibrosis, as determined independently by a hepatopathologist. MR imaging has the potential of offering a comprehensive noninvasive evaluation of patients with suspected cirrhosis, but considerable expertise is required at present.
False Positive Reactions↗
Conventional and fast spin-echo MR imaging: minimizing echo time.
Magnetic resonance imaging is frequently complicated by the presence of motion and susceptibility gradients. Also, some biologic tissues have short T2s. These problems are particularly troublesome in fast spin-echo (FSE) imaging, in which T2 decay and motion between echoes result in image blurring and ghost artifacts. The authors reduced TE in conventional spin-echo (SE) imaging to 5 msec and echo spacing (E-space) in FSE imaging to 6 msec. All magnetic gradients (except readout) were kept at a maximum, with data sampling as fast as 125 kHz and only ramp waveforms used. Truncated sinc radio-frequency pulses and asymmetric echo sampling were also used in SE imaging. Short TE (5.8 msec) SE images of the upper abdomen were compared with conventional SE images (TE = 11 msec). Also, FSE images with short E-space were compared with conventional FSE images in multiple body sites. Short TE significantly improved the liver-spleen contrast-to-total noise ratio (C/N) (7.9 vs 4.1, n = 9, P < .01) on T1-weighted SE images, reduced the intensity of ghost artifacts (by 34%, P < .02), and increased the number of available imaging planes by 30%. It also improved delineation of cranial nerves and reduced susceptibility artifacts. On short E-space FSE images, spine, lung, upper abdomen, and musculoskeletal tissues appeared crisper and measured spleen-liver C/N increased significantly (6.9 vs 4.0, n = 12, P < .01). The delineation of tissues with short T2 (eg, cartilage) and motion artifact suppression were also improved. Short TE methods can improve image quality in both SE and FSE imaging and merit further clinical evaluation.
Abdomen↗
Hybrid RARE: implementations for abdominal MR imaging.
Hybrid RARE (rapid acquisition with relaxation enhancement) is a family of magnetic resonance (MR) imaging techniques whereby a set of images is phase encoded with more than one spin echo per excitation pulse. This increases the efficiency of obtaining T2-weighted images, allowing greater flexibility regarding acquisition time, resolution, signal-to-noise ratio, and tissue contrast. Hybrid RARE techniques involve several important new user-selectable parameters such as effective TE, echo train length, and echo spacing. Choices of other parameters, such as TR, sampling bandwidth, and acquisition matrix, may be different from those of comparable conventional T2-weighted spin-echo images. Different hybrid RARE implementations can be used for abdominal screening, with T2-weighted or T2-weighted and inversion-recovery contrast, or for characterizing liver lesions or imaging the biliary system with an extremely long TE. High-resolution images may be obtained by averaging multiple signals during quiet breathing, or images may be acquired more rapidly during suspended respiration. In this review, the authors discuss the basic principles of hybrid RARE techniques and how various imaging parameters can be manipulated to increase the quality and flexibility of abdominal T2-weighted MR imaging.
Abdomen↗
Pulsatile flow artifacts in fast magnetization-prepared sequences.
Fast magnetization-prepared magnetic resonance imaging sequences allow clinical acquisitions in about 1 second, with the preparation phase providing the desired contrast. Pulsatile flow artifacts, although reduced by rapid acquisition, can degrade image quality. The authors explore the causes of aortic pulsatile flow artifacts in inversion-recovery-prepared acquisitions of the abdomen, taking into consideration various parameters. The flow signal within an 8-mm-thick section was simulated and subsequently Fourier transformed to determine the location and extent of flow artifacts. Results of simulations were validated with abdominal images of human subjects. Recording all encodings within one cardiac cycle reduced pulsatile flow artifacts in nonsegmented acquisitions with sequential phase-encoding order, regardless of the location of magnetization preparation within the cardiac cycle. In segmented acquisitions, however, the sequential order always increased flow artifacts. To reduce the artifacts in short TI acquisitions, the magnetization should be prepared during diastole. In clinical acquisitions, flow artifacts were further reduced by modifying the phase-encoding scheme.
Aorta, Abdominal↗
Pulsation artifact in short TR MR imaging and angiography: exacerbation with signal averaging.
Averaging the signals from more than one excitation per phase-encoding view increases the signal-to-noise ratio and, in conventional spin-echo magnetic resonance imaging, reduces most motion artifacts. To determine the effects of signal averaging on two-dimensional gradient-echo images, acquisitions with different TRs and with no averaging versus multiple-signal averaging were compared in a pulsatile flow phantom and the human abdominal aorta. Intraview (each view repeated before changing the phase-encoding value) and interview (obtaining all views sequentially and then repeating the entire set) averaging methods were used. Pulsation artifacts were present on all images of the flow phantom and the aorta. Intraview signal averaging, the method most commonly used, exacerbated rather than ameliorated pulsation artifacts with short TR sequences. Pulsation artifacts on two-dimensional images obtained with a short TR can be minimized by completing the acquisition as rapidly as possible, avoiding signal averaging. If signal averaging is used for short TR images, it should be interview averaging.
Algorithms↗
MR portography: preliminary comparison with CT portography and conventional MR imaging.
Magnetic resonance (MR) imaging with arterial portography (MRAP) was compared with computed tomography with arterial portography (CTAP) and conventional MR imaging for preoperative evaluation of hepatic masses in eight patients (nine studies). Twenty contiguous, 10-mm-thick-section CTAP images were obtained. MR imaging included T1- and T2-weighted spin-echo and fast multiplanar SPGR (spoiled gradient-recalled acquisition in the steady state) techniques. For MRAP, 0.1 mmol/kg gadopentetate dimeglumine was injected into the superior mesenteric artery. Portographic-phase, 8-mm-thick-section, axial SPGR images were first obtained, followed by "systemic phase" SPGR images. Lesions were seen best on the portographic-phase MRAP images and were less conspicuous on the systemic-phase MRAP, CTAP and conventional MR images. Of 19 visualized lesions, 18 were seen with MRAP; however; five subcentimeter lesions seen with MRAP were not seen with conventional MR imaging or CTAP. Systemic recirculation of iodinated contrast material from the bolus and from previous angiography is a potential limitation of CTAP. For both CTAP and MRAP, optimal results are expected if all images are obtained during a single breath hold, within seconds of the onset of contrast agent administration.
Contrast Media↗
Safety and optimum concentration of a manganese chloride-based oral MR contrast agent.
To determine the safety of a manganese chloride-based oral magnetic resonance (MR) contrast agent and the ideal concentration of the agent for marking in three different anatomic sites (stomach, middle of the small bowel, and ileocecal region), six healthy volunteers were evaluated before and after administration of 900 mL of three different concentrations of the contrast agent. Images were evaluated subjectively and objectively. No adverse events were noted. There was a minimal rise in manganese blood levels at 6 hours after administration, with a return to baseline at 24 hours. The imaging data demonstrated good-to-excellent bowel marking on T1-weighted images at all three concentrations. However, on T2-weighted images, the 40 mg Mn+2/L concentration provided improved hypointense bowel marking relative to the 20 mg/L concentration. Little difference was seen between the 40 and 60 mg/L concentrations. Fast T1- and T2-weighted sequences provided superior image quality to that of conventional spin-echo sequences.
Administration, Oral↗
Delineation of pancreas with MR imaging: multiobserver comparison of five pulse sequences.
The authors compared five magnetic resonance (MR) imaging pulse sequences for their ability to depict the pancreas in 59 patients, each evaluated with at least two of the five sequences. Focal pancreatic carcinomas were present in eight patients. The five sequences were T1-weighted spin echo (T1-SE), fat-suppressed T1-SE (T1-FS), T1-weighted gradient echo (T1-GRE), T2-weighted SE (T2-SE), and T2-weighted fast spin echo (T2-FSE). Using repeated-measures analysis, three blinded observers independently reviewed 198 separate MR imaging series and rated them on a 5-point scale with regard to image quality and depiction of pancreatic borders and the number of sections containing pancreatic and common bile ducts. The most superior and most inferior sections containing pancreas were recorded for each sequence in each patient. The results were compared with analysis of variance, and interobserver agreement was measured with the intraclass correlation coefficient (ICC). For image quality, all sequences were rated good to excellent, with the T1-SE sequence having the highest rating. For clarity of pancreatic borders, however, the T1-FS sequence was rated significantly higher (P < .006) than the other sequences; the T2-SE sequence was least satisfactory. Common bile and pancreatic ducts were seen in the most sections with the T2-FSE sequence. There were no significant differences regarding identification of the most superior and inferior sections containing pancreas, and the ICC was high (.91-.97) for all sequences. For detecting focal carcinomas, no single pulse sequence was sufficient.
Common Bile Duct↗
Pancreatic signal intensity on T1-weighted fat saturation MR images: clinical correlation.
To determine whether signal intensity (SI) of the pancreas that was less than that of liver on T1-weighted fat-suppressed (T1FS) magnetic resonance (MR) images could be used to help predict the presence of pancreatic disease, three blinded independent observers graded pancreatic SI relative to liver and/or renal cortex in 89 patients on T1FS images. Results were correlated with patient age and diagnosis. Among the 47 patients with a clinically normal pancreas, pancreatic SI was higher than that of liver in 42 and equal to that of liver in the rest, none of whom had evidence of fatty pancreas. These five patients had a mean age of 71 years, compared with 55 years for patients whose pancreas was more intense than liver (P = .02). Of the 42 patients with a clinically abnormal pancreas, only eight had pancreatic SI higher than that of liver. The positive predictive value for normal pancreas of an SI higher than that of liver was 84% and the positive predictive value for abnormal pancreas of an SI less than or equal to that of liver was 88%, with an overall accuracy of 86%. If normal pancreatic SI is defined as higher than that of liver for patients younger than 60 years and as equal to or higher than that of liver for patients older than 60 years, the positive predictive value of normal SI becomes 76%, the positive predictive value of decreased SI becomes 100%, and the overall accuracy becomes 83%.(ABSTRACT TRUNCATED AT 250 WORDS)
Adipose Tissue↗
Respiratory and postprandial changes in portal flow rate: assessment by phase contrast MR imaging.
The objective of this study was to investigate the variability of several different phase contrast (PC) magnetic resonance techniques and duplex Doppler imaging (DDI) for measuring portal flow rate (PFR) with different patterns of respiration before and after a standard meal. PFR was measured in nine normal volunteers in both fasting and postprandial states, using both 2D and cine PC MR techniques. Two-dimensional PC technique was performed with and without breath-hold (BH). Four different patterns of BH (relaxed maximal inspiration, expiration, Valsalva maneuver, and Müller or reversed Valsalva) were used. Cine PC technique was performed without BH. DDI measurement of PFR was done in the fasting state with relaxed inspiration. PFR measurements made by means of PC MR techniques varied, depending on BH method, and were systematically less than those obtained by DDI. PFR measured during inspiration was significantly less than that measured during expiration and other respiratory maneuvers (P < .03). PFR increased significantly after a meal for PC and Doppler measurements, with a range of mean increases of 24 to 74%. Two-dimensional PC MR imaging techniques yielded differing measurements of PFR, depending on whether they were done with or without BH, as well as on the pattern of BH. PC mean measures of PFR were consistently less than those of DDI. The physiologic inspiratory decreases and postprandial increases of the PFR were evident from 2D and cine PC MRI techniques, as well as with DDI.
Adult↗
Multilocular cystic nephroma: MR imaging appearance with current techniques, including gadolinium enhancement.
The purpose of the study was to define the MRI appearance of multilocular cystic nephroma (MLCN), using current MR techniques, including gadolinium (Gd)-enhanced sequences. Seven patients with MLCN underwent MR imaging with the following sequences: T1-weighted spin echo with fat suppression (T1FS, five patients), T1-weighted spoiled gradient echo (SGE, seven patients), T2-weighted fast spin echo (two patients), and Gd-enhanced T1FS (seven patients) and SGE (seven patients). MLCN was histologically proven by resection of the mass in six patients and by observation of typical imaging features with stability in appearance over a 6-month period in one patient. Lesion morphology and signal intensity (SI) features were retrospectively evaluated. MRI features of MLCN included a solitary cystic lesion with thin internal septations in six patients and a cluster of closely grouped cysts similar in size in one patient. Individual cystic spaces demonstrated SI, varying from low to high on T1-weighted images in three patients and demonstrated low-to-intermediate SI in four patients. Herniation of the lesions into the renal collecting system and thin enhancing septa were demonstrated in all patients. A complex cystic renal lesion with enhancing septa and herniation into the renal collecting system are the characteristic MR findings of MLCN. The direct multiplanar capability of MR may optimally show the relationship of MLCN to the renal pelvis and, thus, facilitate correct diagnosis.
Adult↗
Fast MR imaging techniques: impact in the abdomen.
The increased efficiency of MRI data acquisition has had a substantial impact on clinical MRI of the abdomen. Five particular applications that have thus been affected include breath-hold imaging of liver lesions (including detection, characterization, and biopsy), MR cholangiopan- creatography, practical chemical shift imaging (including liver and adrenal glands), dynamic imaging after contrast media injection, and MR angiography.
Abdomen↗