Biomedical subjects

G de Geer

Publications and source records attributed to G de Geer.

12 recordsLinked to original sources

PubMed1987

A preliminary study of MRI quantification of simulated calcified pulmonary nodules.

The potential of magnetic resonance imaging (MRI) quantification of calcium for the evaluation of pulmonary nodules was investigated in simulated nodules. Calcium salts do not contain mobile protons and thus have no signal on MR proton images. To determine whether the absence of signal from partially calcified nodules could be quantified, we studied simulated nodules containing known quantities of calcium salts. The soft tissue equivalent material was an agar-gelatin mixture (T1:1100-1500 msec; T2: 59-62 msec). In the first experiments, glass tubes were filled with the mixture, which contained suspensions of calcium carbonate (CaCO3) or silica dioxide (Si02), and were subjected to computed tomography (CT) scanning and MR imaging. In a second series of studies CaCO3 particles of various sizes (and therefore different surface-to-volume ratios) were similarly suspended and subjected to CT scanning and MR imaging. In a third series hydroxyapatite (HA) suspensions of different sizes were similarly studied. CaCO3 produced a significant reduction in MR hydrogen density and signal intensity of the agar-gelatin mixture. Reduction in T1 and T2 relaxation times was inconsistent and not related to particle size. CaCO3 produced its effect by soft-tissue displacement. HA (and Si02) caused a more marked fall in MR hydrogen density, signal intensity, and T1 and T2 relaxation times. The degree of the T1 and T2 effects was related to particle size, indicating a hydrophilic surface effect. The authors conclude that MRI quantification of calcium within pulmonary nodules (or other tissues) will be complex and will relate to the precise composition of the calcium salt and to the particle size of the aggregates.

Calcinosis↗

PubMed1987

Chest wall after mastectomy. Part I. CT appearance of normal postoperative anatomy, postirradiation changes, and optimal scanning techniques.

The computed tomographic (CT) scans of patients with breast carcinoma treated by surgery with and without radiation therapy were reviewed and correlated with clinical status. The optimal techniques of patient examination and the post-therapy findings were analyzed. The brachial injection of intravenous contrast material produced significant artifacts that limited interpretation of the ipsilateral chest wall in all cases and did not give additional information. Scans obtained with the patients' arms placed at their sides resulted in more clearly interpretable scans, especially when arm weakness or lymphedema precluded symmetric elevation of the arms out of the CT gantry. Radiation therapy produced both acute and chronic changes with characteristic CT appearances. The postoperative anatomy varied markedly depending on the previous surgery. Careful clinical correlation with referring physicians was the key to proper scan evaluation.

Adult↗

PubMed1987

Chest wall after mastectomy. Part II. CT appearance of tumor recurrence.

The postoperative computed tomography (CT) scans of 19 patients with breast cancer and suspected local or regional recurrence were reviewed. Recurrence was documented by percutaneous biopsy in 15 and by overwhelming clinical evidence in two. CT correctly identified the sites of recurrence in all 15 biopsy-proved cases. In two patients, suspected areas on CT scans proved to be residual pectoralis muscles. In most cases, the CT findings of recurrence to the skin, subcutaneous fat, pectoralis muscle, axilla, and brachial plexus can be differentiated from the postoperative and postirradiation anatomy.

Breast Neoplasms↗

PubMed1987

Cine CT in obstructive sleep apnea.

The upper airway was evaluated in eight patients with obstructive sleep apnea by using a rapid sequential CT scanner (Imatron C-100). Four patients also had simultaneous polysomnograms to determine the onset of sleep and apnea. The upper airway was scanned while the patient was awake (eight patients), asleep (four patients), and asleep and apneic (eight patients). Measurements of the cross-sectional area of the upper airway were correlated with the findings on sleep studies in four patients. During the awake state the airway was narrowed and showed increased collapsibility in all eight patients. Five of the eight patients had cross-sectional areas of less than or equal to 4 mm2 at one or more sites at some time during the respiratory cycle while awake. During apnea all patients had obstruction at the uvula and oropharynx, but the length of the obstruction varied from one patient to another. In three of the eight patients the obstruction extended inferiorly to the hypopharynx. Cine CT can be used to objectively evaluate patients with sleep apnea and may demonstrate the need to modify surgical treatment.

Adult↗

PubMed1987

Evaluation of pleural and pericardial effusions by magnetic resonance imaging.

MR examinations of 36 patients with pleural and/or pericardial effusions were retrospectively evaluated. The purpose of this study was to determine of MR imaging is capable of differentiating between pleural and pericardial effusions of different compositions using standard electrocardiogram (ECG)-gated and non-gated spin echo pulse sequences. Additional data was obtained from experimental pleural effusions in 10 dogs. The results of this study indicate that old hemorrhages into the pleural or pericardial space can be differentiated from other pleural or pericardial effusions. However, further differentiation between transudates, exudates and sanguinous effusions is not possible on MR images acquired with standard spin echo pulse sequences. Respiratory and cardiac motion are responsible for signal loss, particularly on first echo images. This was documented in experiments in dogs with induced effusions of known composition; "negative" T2 values consistent with fluid motion during imaging sequences were observed in 80% of cases. However, postmortem studies of the dogs with experimental effusions showed differences between effusions with low protein concentrations and higher protein concentrations. We conclude from our study that characterization of pleural and pericardial effusions on standard ECG-gated and non-gated MR examinations is limited to the positive identification of hemorrhage. Motion of the fluid due to cardiac and respiratory activity causes artifactual and unpredictable changes in intensity values negating the more subtle differences in intensity associated with increasing protein content.

Animals↗

PubMed1986

MR imaging of fat.

Fat has been used in many studies on magnetic resonance (MR) imaging as the tissue of reference in comparing regional signal intensities from various tissues using different imaging parameters. This is a retrospective study of 78 patients selected to assess the influence of different factors such as age, gender, obesity, and weight loss on the T1 and T2 relaxation parameters of fat in different areas of the body. The T1 values of fat were not influenced by the factors studied or by anatomic location of the fat. The T2 values were significantly lower in patients older than 65 years and in patients with significant weight loss caused by carcinoma or chronic disease. Nevertheless, these variations were small, with considerable overlap of the mean and rather large standard deviation values. In conclusion, fat is a valuable reference tissue for MR studies and is relatively uninfluenced by the factors studied.

Adipose Tissue↗

PubMed1986

Mediastinal masses: MR imaging.

Seventy-five patients with mediastinal masses were imaged with magnetic resonance (MR). Results were analyzed with regard to the ability of MR to demonstrate the masses, their morphology, and their encroachment or displacement of blood vessels and airways. T1 values were determined in 53 patients and T2 values in 59. Hydrogen density and percentage of contrast relative to muscle and fat were also obtained in 53 and 59 patients, respectively. MR images were compared with computed tomography (CT) scans, which were available in 45 patients. MR depicted all masses and demonstrated compromise of vessels and cardiac chambers owing to the inherent contrast between the masses and cardiovascular structures. Bronchogenic carcinoma had very long relaxation values for T1 and T2, while chronic inflammatory processes had intermediate values for T1 and T2, thus appearing less intense than bronchogenic carcinoma on T2-weighted images. Other neoplasms demonstrated T1 and T2 values between these two disease groups. Masses appeared less homogeneous on MR images than on CT scans, and vascular compromise was better assessed with MR. Thus, MR imaging is a completely noninvasive technique for the evaluation of mediastinal masses. While the anatomic information is comparable to that produced by CT, MR provides some insight into the composition of the mass.

Adolescent↗

PubMed1986

Normal thymus: assessment with MR and CT.

The magnetic resonance (MR) characteristics of the normal thymus in 18 patients were compared with computed tomographic (CT) findings in 13 of the 18. Patients ranged in age from 5 to 77 years. The thymus was visible in all patients and differed from subcutaneous fat in hydrogen density; the average thymus to fat hydrogen density ratio was 0.60. Although the T1 relaxation times of the thymus (mean = 703 msec) were much longer than those of fat (mean = 287 msec) in patients under 30 years of age, this difference decreased with age. The T2 relaxation times of the thymus were similar to those of fat and did not change with age. The thymus appeared thicker on MR images than on CT scans in patients older than 20 years. MR may be better than CT in distinguishing between thymus replaced by fat and mediastinal fat.

Adolescent↗

PubMed1986

Normal and occluded mediastinal veins: MR imaging.

The potential of magnetic resonance (MR) imaging to demonstrate the mediastinal veins was evaluated retrospectively in 25 patients with no evidence of a venous abnormality, 28 patients who had narrowing or occlusion of a mediastinal vein, and two patients who had a venous anomaly. In patients with venous occlusion, the MR images graphically demonstrated the sites and extent. MR images also demonstrated slow flow within venous structures proximal to the obstruction. Generally, venous collaterals in the mediastinum and chest wall were better seen with contrast material-enhanced computed tomography scans. The marked contrast on MR images between the signal void of normal vascular structures, the moderate signal intensity of tumor, and the high signal intensity of a thrombus or slowly flowing blood allows ready detection of venous occlusion and may suggest the nature of the occlusion.

Adolescent↗

PubMed1986

Evaluation of a chest phantom for CT nodule densitometry.

The characteristics of a chest phantom used for CT nodule densitometry were determined by use of a GE CT 9800 scanner (General Electric, Milwaukee, WI). The supplied reference rods were scanned in different positions within the lung fields of the phantom and with varied chest wall thicknesses. The liver/spleen inserts were added. The CT attenuation values of different-size rods and their mineral content were also tested. The size of the standard rod is the major determinant of its CT number, which varied from 1 to 83 H. The standard rods contained no measurable calcium or other mineral. Position-dependent variability in CT numbers was relatively small with the GE CT 9800 scanner. The simulated chest wall additions and liver/spleen inserts produced only small increases in CT density. We conclude that the GE CT 9800 scanner, as an example of one of the newer CT scanners, shows improved operating characteristics for pulmonary nodule densitometry. Nodule densitometry should be further evaluated with simplified phantoms.

Densitometry↗

PubMed1986

MR characteristics of benign lymph node enlargement in sarcoidosis and Castleman's disease.

The magnetic resonance characteristics of mediastinal and hilar lymphadenopathy were reviewed in five patients with sarcoidosis and one with Castleman's disease. Although the T1 values of 26 nodes measured in patients with sarcoidosis ranged from 390 to 786 msec (mean 549 msec; SD 88 msec), the mean values recorded for each patient were quite similar (range 501-616 msec). T2 values ranged from 40 to 68 msec (mean 49 msec; SD 7 msec). In the patient with Castleman's disease T1 and T2 values measured 838 msec and 45 msec respectively. In comparison to T1 and T2 values we have recently measured in patients with proven mediastinal lymph node metastases from bronchogenic carcinoma, lymph nodes in the patients with sarcoidosis have significantly lower T1 (p less than .001) and T2 (p less than .05) values. However, because of significant overlap between the values recorded in these two groups, their differentiation may be difficult in individual cases.

Adult↗

PubMed1985

Bronchogenic carcinoma: staging with MR compared with staging with CT and surgery.

Thirty-three patients suspected of having bronchogenic carcinoma were studied prospectively using magnetic resonance (MR). In this group, 30 underwent examination with computed tomography (CT), 15 underwent thoracotomy, six had mediastinal biopsy procedures performed, and eight underwent bronchoscopy. MR studies, which included transaxial spin-echo imaging (TR, 0.5 and 2.0 sec; TE, 28 and 56 msec) of all patients and sagittal or coronal imaging of 18, were performed without knowledge of CT findings, using only plain radiographs as a guide. CT and MR studies were interpreted separately. CT and MR provided comparable information regarding the presence and size of mediastinal lymph nodes. MR better discriminated mediastinal nodes from vascular structures. However, in two of 11 patients who had multiple mediastinal lymph nodes that were normal in size at CT examination and surgery, MR suggested a confluent abnormal mass, probably because of its poorer spatial resolution. MR was superior to CT in showing enlarged hilar lymph nodes, but CT was better for demonstrating bronchial abnormalities. In three of four patients who had a proved hilar mass with distal obstructive pneumonia, MR (TR, 2.0 sec) helped distinguish between the mass and collapsed lung.

Adult↗