Distinction of long bone stress fractures from pathologic fractures on cross-sectional imaging: how successful are we?

OBJECTIVE: The objectives of our study were to define CT and MRI features that distinguish pathologic fractures from stress fractures and to compare the performance of CT and MRI with radiography. MATERIALS AND METHODS: Two reviewers retrospectively reviewed 45 MR images, 37 CT scans, and 43 radiographs in 59 patients (30 biopsy-proven pathologic fractures and 29 stress fractures followed to resolution). The features observed on MRI were abnormal bone marrow (well-defined, ill-defined); intracortical, periosteal, or muscle T1 or T2 signal; endosteal scalloping; and a soft-tissue mass. The features seen on CT were marrow abnormality and character (well-defined, ill-defined, permeative, moth-eaten), endosteal scalloping, periosteal reaction (benign, aggressive), and a soft-tissue mass. Reviewers rated their confidence for diagnosing a pathologic fracture on a 1-3 scale (< 50%, 50-95%, > 95% sure, respectively) with each technique. Performance of each technique was defined by reviewer accuracy and area under the receiver operating characteristic curve (Az); the frequency with which the MRI and CT features were associated with pathologic and stress fractures was calculated. RESULTS: For both reviewers, accuracy for differentiating pathologic from stress fractures was highest on MRI (accuracy/Az: reviewer 1, 98%/0.97; reviewer 2, 93%/0.99); CT (reviewer 1, 88%/0.83; reviewer 2, 82%/0.90) was less accurate than radiography (reviewer 1, 94%/0.98; reviewer 2, 88%/0.96). On MRI, pathologic fractures compared with stress fractures exhibited well-defined T1 marrow signal (83% vs 7%, respectively; p < 0.001), endosteal scalloping (58% vs 0%, p < 0.001), muscle signal (83% vs 48%, p = 0.026), and a soft-tissue mass (67% vs 0%, p < 0.001). On CT, pathologic fractures compared with stress fractures exhibited marrow abnormality (84% vs 17%, respectively; p = 0.001), endosteal scalloping (44% vs 0%, p = 0.006), and aggressive periosteal reaction (36% vs 0%, p = 0.04). CONCLUSION: MRI is useful for distinguishing pathologic from stress fractures, especially after inconclusive radiographic findings. Specifically, pathologic fractures exhibit well-defined T1 marrow alterations, endosteal scalloping, and adjacent soft-tissue abnormalities.     

Single-vessel coronary artery stenosis: myocardial perfusion imaging with Gadomer-17 first-pass MR imaging in a swine model of comparison with gadopentetate dimeglumine

PURPOSE: To evaluate the ability of Gadomer-17 to depict perfusion defects in a closed-chest swine model of single-vessel coronary artery disease. MATERIALS AND METHODS: Twelve pigs underwent closed-chest placement of a flow reducer for 70%-90% luminal stenosis in the proximal left anterior coronary artery. Magnetic resonance (MR) perfusion imaging with Gadomer-17 and gadopentetate dimeglumine, microsphere blood flow (MBF) testing, and technetium 99m ((99m)Tc) 2 methoxyisobutylisonitrile (MIBI) single photon emission computed tomography (SPECT) were performed during dipyridamole vasodilation. Comparisons of percentage signal intensity (SI) increase (PSIC) in remote and ischemic myocardium were made with repeated measurements analysis of variance after injection of both tracers. RESULTS: Perfusion defects and reduced PSIC in the anterior ischemic versus the inferior remote myocardium could be identified after injection of both Gadomer-17 (PSIC, 66% +/- 30 [mean +/- SD] vs 100% +/- 32, respectively; P <.001) and gadopentetate dimeglumine (PSIC, 49% +/- 31 vs 81% +/- 43, respectively; P <.005). The size of perfusion defect depicted with both tracers was highly correlated with defect size at (99m)Tc MIBI SPECT (r = 0.69, P <.05 for Gadomer-17 and r = 0.60, P =.05 for gadopentetate dimeglumine) and with areas of reduced MBF (r = 0.70, P <.05 for Gadomer-17 and r = 0.80, P <.05 for gadopentetate dimeglumine). PSIC also correlated with MBF (r = 0.89, P <.001 for Gadomer-17 and r = 0.75, P <.001 for gadopentetate dimeglumine). Gadomer-17 allowed differentiation of ischemic from nonischemic myocardium, as demonstrated by reduced PSIC (PSIC, 48% +/- 38 vs 72% +/- 31, respectively; P <.001) until 20 minutes after contrast material injection. In contrast, differentiation of ischemic from nonischemic myocardium was possible only until 55 seconds after injection of gadopentetate dimeglumine (PSIC, 36% +/- 24 vs 56% +/- 27, respectively; P <.005) but not at any time point thereafter. CONCLUSION: With the study conditions, Gadomer-17 provided more prolonged differentiation of ischemic from remote myocardium than that with gadopentetate dimeglumine.     

1999 ARRS Executive Council Award. Contrast-enhanced CT of small hypovascular hepatic tumors: effect of lesion enhancement on conspicuity in rabbits. American Roentgen Ray Society

OBJECTIVE: The purpose of this study was to evaluate the effect of lesion enhancement on the conspicuity of small hypovascular hepatic tumors in an animal model. MATERIALS AND METHODS: Seven VX2 hepatic tumors in five rabbits were imaged. Dynamic contrast-enhanced CT was performed at a single level centered over the lesions at 5-sec intervals for 119 sec after injection of 2 ml/kg i.v. contrast material at 2 ml/sec. Attenuation was measured over time within regions of interest in the tumor and normal liver, aorta, inferior vena cava, and portal vein. Lesion conspicuity, defined as the difference between the attenuation of the uninvolved liver and neoplasm, was calculated. RESULTS: The mean diameter of the tumors on CT was 10 mm (range, 6-15 mm). The tumors appeared as low-attenuation lesions with progressive enhancement during the arterial phase and early portal phase. Peak mean lesion attenuation was 60 +/- 27 H (enhancement, 23 H) at 64 sec. Peak mean lesion conspicuity was 80 +/- 18 H at 39 sec, occurring 10 sec before the peak mean hepatic attenuation of 135 +/- 15 H (enhancement, 67 H) at 49 sec. Relative lesion conspicuity paralleled relative enhancement of the liver throughout the imaging period. CONCLUSION: Although low-level tumor enhancement during the arterial phase and early portal phase reduced the conspicuity of small hypovascular tumors in this animal model, our results support the use of maximum liver enhancement as a marker for peak lesion conspicuity.     

Spatial and temporal resolution in cardiovascular MR imaging: review and recommendations

Because of the nature of digital imaging, the number of pixels in a reconstructed image is often unrelated to the actual spatial resolution of the image. Similarly, the number of reconstructed frames of a dynamic or cine examination can be unrelated to the acquired temporal resolution. These discrepancies can result in misinterpretations and inaccuracies when image resolution is reported in the literature. The goal of this report is to clarify the differences between acquired and displayed resolution, both spatial and temporal, in magnetic resonance imaging. The effects of imaging parameters on acquired resolution are discussed, as are the mathematic effects of the reconstruction process on the displayed resolution of the resulting image. Finally, recommendations to authors are offered to promote accurate and unambiguous reporting of spatiotemporal resolution in the literature.     

Using MRI to assess aortic wall thickness in the multiethnic study of atherosclerosis: distribution by race, sex, and age

OBJECTIVE: Understanding the determinants of subclinical atherosclerosis may aid in elucidating the pathogenesis of atherosclerosis and guide prevention strategies. In this pilot study, we investigated the role of aortic wall thickness as a measure of subclinical atherosclerosis, assessed a method by which to measure aortic wall thickness using MRI, and attempted to define differences in aortic wall thickness by patient race, sex, and age. SUBJECTS AND METHODS. In this prospective study, 196 participants (99 black, 97 white; 98 men, 98 women) were selected from the Multiethnic Study of Atherosclerosis, which consists of participants 45-84 years old without clinical cardiovascular disease, who were recruited from six study centers in the United States. We performed fast spin-echo double inversion recovery MRI to measure thoracic aortic wall thickness. We tested interobserver agreement using the intraclass correlation coefficient, for sex and race differences in wall thickness using the Mann-Whitney test, and for associations between age and wall thickness using linear regression. RESULTS: Reproducibility was excellent for measurements of average and maximal wall thickness on MRI. Average and maximal wall thickness increased with age (p < 0.001 and p = 0.002, respectively). Men had greater mean average wall thickness (2.32 vs 2.11 mm, p = 0.028) and mean maximal wall thickness (3.85 vs 3.31 mm, p = 0.010) than women. Blacks had greater mean maximal wall thickness than whites (3.74 vs 3.42 mm, p = 0.023). CONCLUSION: MRI is a feasible method to measure aortic wall thickness with high interobserver agreement. Aortic wall thickness increases with age and also varies by race and sex.     

Surgically staged focal liver lesions: accuracy and reproducibility of dual-phase helical CT for detection and characterization

PURPOSE: To assess the accuracy and reproducibility of dual-phase helical computed tomography (CT) in enabling preoperative detection and characterization of surgically staged focal liver lesions. MATERIALS AND METHODS: Surgically and histopathologically proven liver lesions were evaluated by three experienced CT readers. These lesions were present in 77 patients who underwent dual-phase helical CT. Images were interpreted separately by the three blinded reviewers. Each lesion was graded on a nine-point scale of confidence, with 1 being definitely benign, 9 being definitely malignant, and 5 being indeterminate. The chi2 test was used to determine if the distribution of lesion classifications was different between readers. RESULTS: There was a total of 237 lesions: 73 were benign and 164 were malignant. Sensitivity for lesion detection was 69%, 70%, and 71% for the three reviewers, respectively. Specificity was 91%, 86%, and 90%, and the area under the curve for the alternative-free response receiver operating characteristic curve was 0.84, 0.83, and 0.85, respectively. The difference in the distributions of lesion classification between the three reviewers was not statistically significant (P =.67) as determined by chi2 analysis. CONCLUSION: Dual-phase CT has sensitivity of 69%-71% and high specificity (86%-91%) in enabling the detection and characterization of focal liver lesions. Interpretation is highly reproducible, as there is minimal variation between experienced reviewers.     

Hepatic MR imaging with ferumoxides: multicenter study of safety and effectiveness of direct injection protocol

PURPOSE: To compare the safety and effectiveness of an undiluted direct injection of ferumoxides with those of a diluted slow infusion of ferumoxides during 30 minutes in patients with known liver lesions or in those suspected of having them. MATERIALS AND METHODS: Two hundred thirty-three patients at 16 institutions were randomized to receive either an undiluted direct injection of 0.56 mg of iron per kilogram of body weight of ferumoxides administered during 2 minutes (2 mL/min) or a diluted slow infusion administered during 30 minutes. Safety was assessed with monitoring for adverse events and laboratory tests. For sensitivity, specificity, and accuracy analysis, two independent blinded observers identified and classified lesions as benign or malignant with precontrast images and with pre- and postcontrast images combined. RESULTS: There was no statistically significant difference in adverse events in the group with direct injection compared with those in the group with infusion (21 [18%] of 114 patients vs 19 [17%] of 112 patients, respectively). No serious adverse events were observed. The most common adverse events in the group with direct injection versus the group with infusion were headache (five [4%] of 114 vs three [3%] of 112, respectively) and back pain (five [4%] of 114 vs three [3%] of 112, respectively). Overall, in 68 (62%) of 109 patients with direct injection and 71 (66%) of 108 patients with infusion, additional magnetic resonance (MR) imaging information was obtained after ferumoxides administration (P =.67). Sensitivity, specificity, and accuracy for the diagnosis of malignancy were significantly improved by adding images obtained after ferumoxides administration to the images obtained before contrast agent administration (P <.05 for all comparisons). CONCLUSION: Direct injection of ferumoxides has safety and effectiveness profiles similar to those of slow infusion of the agent. Further findings indicate that the addition of ferumoxides increases the sensitivity and specificity of hepatic MR evaluation when compared with unenhanced MR imaging.