1989 ARRS Executive Council Award. Exercise-enhanced MR imaging of variations in forearm muscle anatomy and use: importance in MR spectroscopy

31P MR spectroscopic studies of forearm exercise frequently assume that the volume sampled is appropriate for the muscle of interest and that individual variations in muscle anatomy and use are not important. Postexercise MR imaging was used to assess variations in the size, location, and use of forearm flexors and the accuracy of palpation as a method for locating the muscle of interest. By using the information obtained with MR, the effects of errors in surface-coil position relative to the muscle of interest on 31P MR spectroscopy were examined. In the midforearm of seven men, the greatest diameter of the flexor carpi ulnaris was 29 +/- 4 mm, and that of the flexor digitorum superficialis was 28 +/- 6 mm. However, in the proximal forearm, 58 +/- 10% of the diameter was covered by the palmaris longus, when present (79% of subjects). An unexpected finding was that a focal portion of the superficial finger flexor was used primarily as a wrist flexor in 26% of subjects. Palpation incorrectly identified flexor muscle margins by more than 15 mm in 50% of attempts. When a surface coil was positioned over wrist flexors during handgrip, attenuation of exercise-induced changes in 31P spectra resulted. Exercise-enhanced MR imaging reveals variations in forearm muscle anatomy and use that are common and difficult to appreciate by palpation. It therefore allows improved localization of the sensitive volume for MR spectroscopic studies of muscle physiology.     

1990 ARRS Executive Council Award. Intravascular sonography in the detection of arteriosclerosis and evaluation of vascular interventional procedures.

The purpose of this study was to evaluate the use of intravascular sonography for the detection of arteriosclerosis and to determine the effects of vascular interventional procedures on the arterial wall. A catheter-based 20-MHz transducer was used. Forty patients were studied. Twelve had clinical evidence of peripheral vascular disease, 13 were healthy renal donors, and 15 underwent vascular interventional procedures. The aorta and the ipsilateral iliac artery were examined in real time under fluoroscopic guidance and the results were compared with angiography. Sonography in eight of the 13 renal donors showed arterial wall abnormalities in the absence of angiographic evidence of disease. Sonography of the 15 patients after angioplasty or atherectomy demonstrated plaque fractures, intramural dissections, or atherectomy grooves. Our experience suggests that intravascular sonography is of value in reducing the use of angiography to monitor progress or complications of vascular interventional procedures.     

MR diagnosis of pancreatic transplant rejection

To determine the role of MR imaging in the assessment of pancreatic transplant rejection, we prospectively obtained 13 MR scans in nine transplant patients. The presence of rejection was verified pathologically by pancreatic transplant biopsies in five patients. In two additional patients, rejection was proved by concordant renal transplant biopsy as well as by compatible clinical and laboratory data. In the remaining two patients, in whom no biopsy was done, clinical and laboratory data showed no evidence of rejection. The mean T2 of the seven pancreata undergoing rejection was significantly elevated (86 msec) compared with the mean T2 of the two transplants not undergoing rejection (59 msec) (p less than .002). These preliminary results suggest that MR may be useful in the noninvasive diagnosis of pancreatic rejection.     

1999 ARRS Executive Council Award. Creation of saccular aneurysms in the rabbit: a model suitable for testing endovascular devices. American Roentgen Ray Society

OBJECTIVE: This study developed an animal model of intracranial aneurysms suitable for evaluating emerging endovascular devices for aneurysmal therapy. We characterized the short-, medium-, and long-term attributes of this endovascular technique for saccular aneurysmal creation in the rabbit. MATERIALS AND METHODS: The right common carotid artery was surgically exposed in nine New Zealand white rabbits. Using endovascular techniques, we occluded the origin of the right common carotid artery with a pliable balloon. Elastase was incubated endoluminally in the proximal common carotid artery above the balloon. The common carotid artery was ligated distally. Animals were studied angiographically and sacrificed at 2 weeks (n = 3), 10 weeks (n = 3), and 24 weeks (n = 3) after aneurysm creation. Histology was obtained. RESULTS: Saccular aneurysms formed in eight of the nine rabbits. The aneurysm projected from the apex of an approximately 90 degree curve of the parent vessel, the brachiocephalic artery. Mean aneurysm diameter was 4.5 mm (SD, 1.2 mm), and mean height was 7.5 mm (SD, 1.6 mm). All samples showed thinned elastic lamina and no evidence of inflammation. In four of eight aneurysms, unorganized thrombus was present in the dome of the aneurysm. CONCLUSION: Arterial aneurysms with intact endothelium and deficient elastic lamina were reliably created in an area of high shear stress in New Zealand white rabbits. Three of these aneurysms remained patent for at least 6 months. We found a simple procedure that can be readily applied to the testing of new endovascular devices for a reliable creation of aneurysms in rabbits.     

Characterization of tumor hypoxia by 31P MR spectroscopy.

Tumor hypoxia is of considerable importance to the oncologist in selecting and optimizing cancer therapy, because hypoxia can determine the effectiveness of various therapies. The relationship between tumor hypoxia and tumor bioenergetics, assessed by 31P MR spectroscopy, is examined to determine whether 31P MR spectroscopy can be clinically useful to measure or characterize tumor hypoxia. Work with experimental tumors has suggested that several different types of hypoxia may exist and that 31P MR spectroscopy cannot be used to characterize all types. Metabolic hypoxia is the level of hypoxia that results in mitochondrial impairment in cells, and it is associated with declining cellular bioenergetic status, which can be measured by enzymatic assay of adenosine triphosphate (ATP). Because 31P MR spectroscopy is sensitive to levels of ATP, it is potentially sensitive to metabolic hypoxia in vivo and may provide a rapid and noninvasive technique for characterizing metabolic hypoxia in tumors. Radiobiologic hypoxia is the level of hypoxia that results in attenuated cell death due to radiation, because radiotoxicity is directly related to tissue levels of oxygen. Radiobiologic hypoxia of tumors thus has more impact on choice of therapy, yet the relationship between metabolic hypoxia and radiobiologic hypoxia remains to be elucidated. An analysis of published data suggests that 31P MR spectroscopy is directly sensitive to metabolic hypoxia in tumors, but it is only indirectly sensitive to radiobiologic hypoxia in tumors. Therefore, 31P MR spectroscopy may be unable to quantify the cell fraction of a tumor that has radiobiologic hypoxia. However, preliminary data suggest that MR spectroscopy may prove useful for determining the effectiveness of therapeutic interventions designed to manipulate radiobiologic hypoxia in tumors or for monitoring the kinetics of tumor reoxygenation after treatment.     

Renal transplant evaluation with MR angiography and MR imaging.

Magnetic resonance (MR) angiography is a widely used, noninvasive tool for evaluating the aorta and its branches. It is particularly useful in renal transplant recipients because it provides anatomic detail of the transplant artery without nephrotoxic effects. Volume rendering is underutilized in MR angiography, but this technique affords high-quality three-dimensional MR angiograms, especially in cases of tortuous or complex vascular anatomy. An imaging protocol was developed that includes gadolinium-enhanced MR angiography of the transplant renal artery with volume rendering and multiplanar reformation postprocessing techniques. Axial T2-weighted and contrast material-enhanced T1-weighted MR images are also obtained to examine the renal parenchyma itself and to evaluate for hydronephrosis or peritransplant fluid collections. This imaging protocol allows rapid global assessment of the renal transplant arterial system, renal parenchyma, and peritransplant region. It can also help detect or exclude many of the various causes of renal transplant dysfunction (eg, stenosis or occlusion of a transplant vessel, peritransplant fluid collections, ureteral obstruction). Conventional angiography can thus be avoided in patients with normal findings and reserved for those with MR angiographic evidence of stenosis.     

Evaluations of cooling exercised muscle with MR imaging and 31P MR spectroscopy

PURPOSE: To investigate the effects of cooling human skeletal muscle after strenuous exercise using 31P MR spectroscopy and MR imaging. METHODS: 14 male subjects (mean age +/- SD, 23.8 +/- 2.3 yr) were randomly assigned to the normal (N = 7) or the cooling group (N = 7). All subjects performed the ankle plantar flexion exercise (12 repetitions, 5 sets). Localized 31P-spectra were collected from the medial gastrocnemius before and after exercise (immediately, 30, 60 min, 24, 48, 96, and 168 h) to determine the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) and intracellular pH. Transaxial T2-weighted MR images of the medial gastrocnemius were obtained to calculate T2 relaxation time (T2), indicative of intramuscular water level, before and after exercise (24, 48, 96, and 168 h). In addition, the muscle soreness level was assessed at the same time as 31P-spectra measurements. Fifteen-minute cold-water immersion was administered to the cooling group after exercise and initial postexercise measurements. RESULTS: The control group showed significantly increased T2 from rest at 48 h after exercise (P < 0.05), but the cooling group showed no significant change in T2 throughout this study. Both groups showed a significantly decreased intracellular pH immediately after exercise (P < 0.05). After that, the cooling group showed a significantly greater value than the value at rest or the control group at 60 min after exercise (P < 0.05). For the Pi/PCr, no significant change was observed in both groups throughout this study. The muscle soreness level significantly increased immediately and at 24-48 h after exercise in both groups (P < 0.05). CONCLUSION: The findings of this study suggest that cooling causes an increase in intracellular pH and prevents the delayed muscle edema.     

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.     

Thickened submucosal layer: a sonographic sign of acute gastrointestinal abnormality representing submucosal edema or hemorrhage. 2000 ARRS Executive Council Award II. American Roentgen Ray Society

OBJECTIVE: We correlated the sonographic appearance of bowel wall thickening with the acuity of the underlying disease process. SUBJECTS AND METHODS: Sonograms of thickened bowel walls were reviewed in 37 patients with proven gastrointestinal abnormalities. Sonographic findings were correlated with clinical presentation, endoscopy, histology, laboratory data, barium studies, and CT. RESULTS: Twenty-eight patients presented acutely, and nine patients had chronic or subacute disease processes. Two of the 28 patients had concurrent acute and chronic processes. In 27 of 28 patients with acute processes, the abnormal bowel segments were characterized by an echogenic submucosal layer thicker than 2.5 mm. In contrast, nine patients with chronic or subacute processes had relatively uniform hypoechoic thickening of the bowel wall with loss of visualization of a discrete echogenic submucosal layer. CT was available for comparison in 30 of 37 patients. Of the 28 patients with acute abnormalities, the thickened echogenic submucosal layer on sonography corresponded to either low-attenuation submucosal edema (n = 25) or acute submucosal hemorrhage (n = 3). CONCLUSION: The finding of a thickened submucosal layer suggests an acute disease process of the bowel and corresponds to either submucosal edema or hemorrhage.     

Renal transplant dysfunction: MR evaluation

The results of 45 MR examinations were prospectively compared with the clinical course and biopsy results in 38 renal transplant patients to determine the role of MR in evaluating allograft dysfunction. Twenty-six patients underwent allograft biopsy. In eight patients in whom the biopsy was performed more than 48 hr after MR examination and in 19 patients who did not have a biopsy, the subsequent clinical course was sufficiently diagnostic to determine the specific cause of the transplant dysfunction. Corticomedullary differentiation, graded from 0 to 3, was not helpful in separating rejection (n = 20) from acute tubular necrosis (n = 9), drug toxicity (n = 7), pyelonephritis (n = 2), or normal grafts (n = 7) because of overlap between groups (sensitivity =; 60%, specificity = 60%). In the six patients with two or more MR studies, serial changes in corticomedullary differentiation were not consistent and could not be used to diagnose rejection. When any abnormality of allograft sinus fat, size or shape, or corticomedullary differentiation was considered, the sensitivity for the diagnosis of rejection approached 80%; however, specificity was low (48%). We conclude that MR imaging is not sufficiently accurate to replace transplant biopsy and therefore has a limited role in the evaluation of transplant dysfunction.     

Bone and soft-tissue lesions: diagnosis with combined H-1 MR imaging and P-31 MR spectroscopy

The feasibility of combined magnetic resonance (MR) imaging and surface coil phosphorus-31 MR spectroscopy at 1.5 T was examined in a clinical study of 34 patients before biopsy of bone or soft-tissue lesions of the extremity and trunk. The results confirmed the inability of MR imaging alone to distinguish most benign lesions from malignant ones. Malignant lesions were distinguished from benign lesions on the basis of significantly higher mean peak ratios of phosphomonoester (PME) to beta-nucleoside triphosphate (NTP) and of phosphodiester to NTP, a significantly lower mean peak area ratio of phosphocreatine to NTP, and a higher mean pH. The diagnostic performance of the PME/NTP peak area ratio is characterized by a sensitivity (true-positive fraction) of 1.00 and a specificity (true-negative fraction) of 0.93. This study provided preliminary evidence that P-31 MR spectroscopy may be used to improve diagnostic specificity in bone and soft-tissue lesions.     

Abnormal testicular function: potential of P-31 MR spectroscopy in diagnosis

Phosphorus-31 MR spectroscopy of the human testis was performed on healthy volunteers (n = 17) and oligospermic (n = 7) and azoospermic patients (n = 4). All patients in the latter group had the Sertoli-cell-only syndrome. Determination of the ratios of phosphomonoesters (PMs) to adenosine triphosphate (ATP), phosphodiesters (PDs) to ATP, and inorganic phosphate (Pi) to ATP made it possible to discriminate among these three groups. The testicular PM/ATP ratio was 1.71 +/- 0.03 (mean +/- standard deviation) in the healthy volunteers and dropped to 1.41 +/- 0.06 (P less than .001 in comparison with healthy volunteers) in the oligospermic patients and to 1.22 +/- 0.07 (P less than .001) in the azoospermic patients. The testicular PD/ATP ratio did show a slight increase from 0.52 +/- 0.10 in healthy volunteers to 0.68 +/- 0.09 (not significant) for oligospermic patients and to 0.83 +/- 0.10 (P less than .01) for azoospermic patients. The Pi/ATP ratio did not show significant differences between healthy volunteers (0.12 +/- 0.07) and oligospermic patients (0.23 +/- 0.08) but was elevated in the azoospermic patients (0.79 +/- 0.12) (P less than .001).     

31P MR波谱在骨恶性肿瘤与炎症鉴别中的应用

目的 探讨活体31P MR波谱(31P MRS)在骨恶性肿瘤与炎症鉴别中的价值.方法 对32名健康志愿者、20例恶性骨肿瘤、22例骨及软组织炎症患者分别行常规X线、MRI与31P MRS 检查,测定波谱中各代谢产物的峰下面积,计算各代谢产物间的比值,并根据无机磷(Pi)相对于磷酸肌酸(PCr)的化学位移测定细胞内pH值.统计学采用单因素方差分析.结果 31P MRS检测发现恶性骨肿瘤组磷酸单酯(PME)/β-三磷酸腺苷(ATP)值(1.24±0.37)明显高于对照组和炎症组(P值均＜0.01);炎症组磷酸二酯(PDE)/β-ATP(2.21±0.37)、Pi/β-ATP(1.46±0.43)明显高于对照组和恶性肿瘤组(P值均＜0.05),但PME/β-ATP(0.19±0.10)值不高;对照组低能磷酸盐(LEP)/总31P代谢物(T31P)(0.10±0.02)、PCr/T31p(0.45±0.03)、ATP/T31P(0.45±0.03)与恶性骨肿瘤和炎症组之间差异有统计学意义(P值均＜0.01);恶性肿瘤组细胞内pH值为7.45±0.16,明显高于正常对照组(7.05±0.06)和炎症组(7.20±0.13)(P值均＜0.01).结论 组织中PME和细胞内pH值的升高对恶性骨肿瘤的诊断有重要意义.MRS技术与常规X线、MRI相结合,有助于临床对恶性骨肿瘤与炎症的鉴别.     

A comparison of MR elastography and 31P MR spectroscopy with histological staging of liver fibrosis

Objectives

Conventional imaging techniques are insensitive to liver fibrosis. This study assesses the diagnostic accuracy of MR elastography (MRE) stiffness values and the ratio of phosphomonoesters (PME)/phosphodiesters (PDE) measured using ³¹P spectroscopy against histological fibrosis staging.

Methods

The local research ethics committee approved this prospective, blinded study. A total of 77 consecutive patients (55 male, aged 49 ± 11.5 years) with a clinical suspicion of liver fibrosis underwent an MR examination with a liver biopsy later the same day. Patients underwent MRE and ³¹P spectroscopy on a 1.5 T whole body system. The liver biopsies were staged using an Ishak score for chronic hepatitis or a modified NAS fibrosis score for fatty liver disease.

Results

MRE increased with and was positively associated with fibrosis stage (Spearman’s rank = 0.622, P < 0.001). PME/PDE was not associated with fibrosis stage (Spearman’s rank = −0.041, p = 0.741). Area under receiver operating curves for MRE stiffness values were high (range 0.75–0.97). The diagnostic utility of PME/PDE was no better than chance (range 0.44–0.58).

Conclusions

MRE-estimated liver stiffness increases with fibrosis stage and is able to dichotomise fibrosis stage groupings. We did not find a relationship between ³¹P MR spectroscopy and fibrosis stage.

Key Points

• Magnetic resonance elastography (MRE) and MR spectroscopy can both assess the liver.

• MRE is superior to ³¹ P MR spectroscopy in staging hepatic fibrosis.

• MRE is able to dichotomise liver fibrosis stage groupings.

• Gradient-echo MRE may be problematic in genetic haemochromatosis.

     

Breast tumors: evaluation with P-31 MR spectroscopy

Differences in the energetics of breast carcinomas and benign breast tumors were monitored by recording their high-energy phosphate concentrations using phosphorus-31 magnetic resonance (MR) spectroscopy. Analysis of the P-31 spectra of biopsy samples from five benign breast tumors and nine breast carcinomas showed that the concentrations of nucleoside triphosphates and phosphomonoesters are consistently higher in the carcinomas than in the benign tumors by an average factor of about three. In addition, the chemical shift differences between the alpha-adenosine triphosphate (alpha-ATP) and beta-ATP signals and between the gamma-ATP and beta-ATP signals were larger by about 0.2 ppm in the carcinomas. These differences result from the lower fraction of magnesium-bound ATP found in the carcinomas under our experimental conditions and reflect a decrease of about two in the concentration of free magnesium ions in the carcinomas relative to that in the benign tumors. Despite the limited number of tumors studied, the results suggest that in vivo P-31 MR spectroscopy may become a reliable method for the diagnosis of breast tumors.     

Evaluation of the lower extremity veins in patients with suspected pulmonary embolism: a retrospective comparison of helical CT venography and sonography. 2000 ARRS Executive Council Award I. American Roentgen Ray Society

OBJECTIVE: In patients undergoing a combined CT angiographic and CT venographic protocol, the accuracy of helical CT venography for the detection of deep venous thrombosis was compared with that of lower extremity sonography. MATERIALS AND METHODS: Patients who had undergone a combined CT angiographic and CT venographic protocol and sonography of the lower extremities within 1 week were identified. The final reports were evaluated for the presence or absence of deep venous thrombosis. Statistical measures for the identification of deep venous thrombosis with helical CT venography were calculated. In each true-positive case, the location of the thrombus identified with both techniques was compared. All false-positive and false-negative cases were reviewed to identify the reasons for the discrepancies. RESULTS: Seventy-four patients were included. There were eight patients (11%) with true-positive findings, 61 patients (82%) with true-negative findings, four patients (5%) with false-positive findings, and one patient (1%) with a false-negative finding. When comparing helical CT venography with sonography for the detection of lower extremity deep venous thrombosis, the sensitivity measured 89%; specificity, 94%; positive predictive value, 67%; negative predictive value, 98%; and accuracy, 93%. Of the eight true-positive cases, five had sites of thrombus that were in agreement on both CT venography and sonography. Of the five discordant cases, four were false-positives and one was a false-negative. Possible explanations for all discrepancies were identified. CONCLUSION: Compared with sonography, CT venography had a 93% accuracy in identifying deep venous thrombosis. However, the positive predictive value of only 67% for CT venography suggests that sonography should be used to confirm the presence of isolated deep venous thrombosis before anticoagulation is initiated. In addition, interpretation of CT venography should be performed with knowledge of certain pitfalls.