Quantitative computed tomography scanning for measurement of bone and bone marrow fat content. A comparison of single- and dual-energy techniques using a solid synthetic phantom

Quantitative CT (QCT) has become a popular method for estimating bone mineral content. In addition, QCT can be used to estimate the fat content of trabecular bone. Although the latter has received little attention, it may prove to be clinically significant. Using a set of custom-built, tissue-mimicking plastic inserts in an anthropomorphic phantom, we tested a variety of methods for estimating mineral and fat content. We also investigated the influence of patient size, reconstruction circle size, and reference phantom choice on the accuracy of the results. Best estimates were obtained when there was a match between patient and reconstruction circle size. Single-energy methods yielded the best estimates of mineral content for inserts that did not contain fat, and dual-energy methods yielded the best estimates for inserts that contained fat. A dual-energy method that we developed was best in estimating the mineral and fat content of the latter inserts. We found that an external calibration reference phantom containing aqueous solutions of K2HPO4 could be used satisfactorily to estimate the mineral content of trabecular bone mimicking inserts; however, more representative materials must be used for accurate estimates of fat content.

Percutaneous biopsy of the cervical spine using CT guidance

CT was used during the percutaneous needle biopsies of seven cervical spine lesions. Four were primary bone tumors, and there was one case each of metastasis, fibrous dysplasia, and infection. Two of the lesions were located in the lateral masses of C1 and one was in the pedicle of C2. The other four were in the lower cervical spine (C4-C6). Accurate diagnosis was obtained on the first attempt in six (86%) of seven cases. No complications were encountered. This experience suggests that needle biopsy performed with CT guidance is both safe and effective.

Tumors of the musculoskeletal system: magnetic resonance imaging and computed tomography

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Osteoporosis in men with idiopathic hypogonadotropic hypogonadism

To assess the effect of testosterone deficiency on skeletal integrity in men, we determined bone density in 23 hypogonadal men with isolated gonadotropin-releasing hormone deficiency and compared those values with ones from controls. Cortical bone density, as assessed by single-photon absorptiometry of the nondominant radius, ranged from 0.57 to 0.86 g/cm2 (mean +/- SE, 0.71 +/- 0.02) in patients with fused epiphyses and from 0.57 to 0.67 g/cm2 (mean, 0.61 +/- 0.01) in patients with open epiphyses, both of which were significantly (p less than 0.001) lower than normal. Spinal trabecular bone density, as assessed by computed tomography, was similarly decreased (p less than 0.0001) and ranged from 42 to 177 mg K2HPO4/cm3 (mean, 112 +/- 7). Cortical bone density was at least 2 SD below normal in 16 of 23 men, and 8 men had spinal bone densities below the fracture threshold of 80 to 100 mg K2HPO4/cm3. Osteopenia was equally severe in men with immature and mature bone ages, suggesting that abnormal bone development plays an important role in the osteopenia of men with idiopathic hypogonadotropic hypogonadism.

Two postprocessing CT techniques for determining the composition of trabecular bone

Two dual-energy CT techniques have been developed to analyze the mineral and fat content of trabecular bone. Both are postprocessing techniques that employ calibration standards. Experiments were performed to test these techniques against conventional single-energy techniques and two other dual-energy techniques. As expected, all of the dual-energy methods estimate the mineral content more accurately when fat is present. In contrast to the other dual-energy methods, the new methods described in this article are unique because they make a separate estimate of the fat content of the bone. The results of preliminary tests of these techniques in estimating fat content have been encouraging. Although not exact, the estimates show the correct trend in increasing proportionately as the fat content increases. Possible applications of the techniques in the study of osteoporosis and other bone diseases are described.

Magnetic resonance imaging of the extremities

MRI offers the best soft-tissue contrast of any radiographic modality. It provides better delineation of soft-tissue tumors and bone tumors than CT, but several different pulse sequences may be needed to make optimum use of this potential. MRI is also well suited to evaluation of abnormalities of the bone marrow, as it is not subject to the dense bone artifact that may occur with CT. Changes in signal intensity may be used to gain some appreciation of blood flow in the major vessels. Examples of each of these applications are discussed.

Restoration of spinal bone in osteoporotic men by treatment with human parathyroid hormone (1-34) and 1,25-dihydroxyvitamin D

Daily subcutaneous injection of a synthetic human parathyroid hormone fragment, combined with daily ingestion of 1,25(OH)2 vitamin D, significantly increased trabecular bone density in the spine (p less than .01), and improved intestinal calcium and phosphorus absorption and total body retention of dietary calcium and phosphorus in middle-aged men with idiopathic osteoporosis. The increases in spinal bone mineral were marked and progressive during a year of treatment. These results indicate that increasing intestinal absorption of dietary calcium while simultaneously stimulating new bone formation with small doses of parathyroid hormone can restore spinal bone in osteoporotic men.

Computed tomography analysis of bone tumors: patterns of cortical destruction and soft tissue extension

Computed tomography was used to identify three different ways in which primary bone tumors may transgress a bony cortex. Analysis of the pattern of cortical transgression was used in conjunction with the presence or absence of matrix mineralization to classify correctly the lesion into one of four different diagnostic categories in 84% of 72 cases. These data demonstrate that certain types of behavior characterize the lesions under discussion and that this information may be helpful in diagnosis.

Evaluation of Gaucher disease using magnetic resonance imaging

Magnetic resonance imaging was used to study the skeletal involvement in a series of twenty-four patients with Gaucher disease. Many sites in the marrow of these patients were characterized by an abnormally low signal intensity that reflected shortened T1 and markedly shortened T2 values in the replaced marrow. The abnormality was non-homogeneous in distribution. In the lower extremity, the proximal (femoral) areas were more frequently affected than the distal (tibial) sites. The epiphyses were generally spared unless the involvement of bone was extensive. Lack of epiphyseal involvement on the magnetic resonance images generally precluded any suspicion of osteonecrosis. The extent of involvement, as suggested by the magnetic resonance data, appeared to correlate well with the occurrence of musculoskeletal complications. Magnetic resonance imaging is more sensitive than computerized tomography in demonstrating the extent of abnormalities in patients with Gaucher disease, and it may have prognostic value.

Sacrococcygeal chordoma: magnetic resonance imaging and computed tomography

Magnetic resonance imaging (MRI) was compared to computed tomography (CT) in four cases of sacrococcygeal chordoma. Both techniques yielded important anatomic information and represented important advances over early radiologic imaging methods. MRI provides superior contrast with surrounding soft tissues because of the prolonged T1 and T2 times of the tumors. This was especially important in a case of recurrent chordoma. The direct sagittal images obtained by MRI were valuable in determining the extent of lesions. Either MRI or direct CT coronal images were needed for the demonstration of tumor involving the sacral nerve roots. It was not possible to reliably distinguish between tumor adherent to bowel wall and bowel wall invasion by either technique. It is concluded that MRI is at least equal to CT for demonstration of these lesions and seems likely to become the imaging method of choice.

Computed tomography of orthopedic neoplasms

CT facilitates diagnosis of orthopedic neoplasms by recognition of both the internal contents of the lesion and its borders with surrounding soft tissues. Involvement of adjacent vital organs and spread within the medullary canal are important for planning resection or amputation. Changes in the size of the lesion may be seen on CT scans following radiation therapy, and metastatic lesions to bone and lungs may be detected with high sensitivity. Biopsy performed with CT guidance is both safe and effective.

High-resolution surface-coil imaging of lumbar disk disease

Seventeen patients with lumbar disk disease were studied using a prototype magnetic resonance (MR) surface coil. The high signal-to-noise ratio achieved with the surface coil permitted increases in spatial resolution to 0.9 X 0.9 mm in-plane resolution with 5 mm slice thickness. The surface coil was also compatible with multiplanar, multiecho imaging techniques. The spatial resolution achieved in this study was nearly equivalent to that achieved by state-of-the-art computed tomographic (CT) scanners, and MR showed a superior range of soft-tissue contrast. One significant limitation of MR was its inability to demonstrate small calcifications. Nevertheless, MR imaging provided diagnostic information comparable to CT or myelography in a completely noninvasive manner. With further technical advances, MR is likely to become the initial procedure of choice for evaluating patients with suspected lumbar disk disease.

Quantitative computed tomography for spinal density measurement. Factors affecting precision

Quantitative computed tomography (QCT) was performed in duplicate on 84 patients to test the short-term precision of the technique. Statistical analysis of the data revealed that precision was not a function of spinal density. It appeared to be worse in osteopenic individuals only when expressed as a percentage. Precision was slightly better in male than in female patients. There is a 90% likelihood that a duplicate measurement will fall within 20 CT units of the first determination in female patients and within ten units in male patients.

Magnetic resonance imaging in a patient with soft tissue sarcoma of the leg

A patient with a high grade malignant fibrous histiocytoma of the leg is presented. Staging studies included a 99mTc diphosphonate bone scan, an arteriogram, a computed tomogram (CT) and a proton (1H) magnetic resonance imaging (MRI) study. By manipulating imaging parameters to enhance contrast between normal and neoplastic tissues, the latter technique more accurately delineated the extent of the soft tissue sarcoma than the other imaging modalities. Although spatial resolution of MRI is inferior to that of CT, it is likely that MRI will provide important information relative to surgical staging and preoperative planning that is not available from current imaging techniques.

The evaluation of musculoskeletal disease with magnetic resonance imaging

Magnetic resonance imaging (MRI) techniques provide a versatile method of manipulating soft tissue contrast in the extremities. Different pulse sequence techniques are discussed with respect to the optimization of contrast differences between muscle, marrow, and abnormal tissue.

Avulsion fracture of the fifth metatarsal: experimental study of pathomechanics

The commonly seen transverse fracture through the base of the fifth metatarsal is neither a Jones fracture nor an avulsion by the peroneus brevis tendon. This fracture was produced in cadaver feet, and it was demonstrated by computed tomography and dissection that the probable cause is avulsion by the lateral cord of the plantar aponeurosis.

Evaluation of multiplanar reconstruction in CT recognition of lumbar disk disease

Axial computed tomographic (CT) images were compared with sagittal and coronal reformations and myelograms in 60 patients to evaluate the diagnostic usefulness of multiplanar reconstructions for the recognition of lumbar disk disease. The axial CT scans were most sensitive and specific. The sagittal scans were helpful in evaluating the neural foramina, the size of the disk bulge into the spinal canal, especially at L5-S1, and patients with spondylolisthesis. The coronal images were the least informative, although they contributed to the evaluation of lumbar nerve roots. The myelograms and the sagittal images were equally useful in the detection of herniated disk, but axial scans were superior to either. It was concluded that reformatted sagittal and coronal images are not required if all axial images are normal. However, when uncertainty exists or complex anatomy is being evaluated, reformatted images may be helpful, particularly for reassurance.

Evaluation of postoperative osteomyelitis of the sternum using tomography and computerized tomography

Thirty-five patients were evaluated for possible postoperative sternal osteomyelitis by tomography. Frank bone destruction and severe demineralization were the only radiologic signs that helped to distinguish patients with sternal osteomyelitis from those with infections limited to soft tissues. We report a patient in whom sternal osteomyelitis was shown by computerized tomography (CT). This observation suggests that CT may provide added information, especially if the sternum is severely demineralized.

"Handedness" of spiral fractures of the tibia

"Handedness" is a basic property of spirals. In many cases it is possible to determine whether spiral fractures are right or left handed by analysis of radiographs. Spiral fractures of the tibia show striking bilateral symmetry, with right-handed spirals predominating on the left side of the body, and left-handed spirals on the right.

Chondrosarcoma: correlation of radiological and histological grade

The radiographic and CT appearance of 20 cases of chondrosarcoma were correlated with histological grade and type of matrix. Features which were useful in predicting histological grade included (a) margins between bone and tumor (radiograph), (b) morphology of calcification (radiograph, CT), (c) distribution of calcification within the lesion (radiograph, CT), (d) pattern of tumor growth within soft tissues (CT), and (e) presence of necrosis (CT). Tumor/soft-tissue margins were usually well defined on the CT scan regardless of grade.