Osteomyelitis: Sensitivity of 0.064 T MRI, three-phase bone scanning and indium scanning with biopsy proof

We compared the ability of magnetic resonance imaging (MRI) using a 0.064 T permanent magnet, three-phase bone scanning, and indium-labeled white blood cell (¹¹¹In-WBC) scanning, to diagnose osteomyelitis. Twenty-three patients underwent biopsy. All patients were examined at presentation with all three modalities. Sensitivities for each modality were calculated using biopsy as a gold standard. The results were 72% for MRI, 68% for bone scan, and 45% for ¹¹¹In-WBC. Specificities were not calculated because of lack of negative biopsies. MRI was as sensitive as bone scanning in the diagnosis of osteomyelitis. All modalities had lower than previously reported sensitivities for imaging osteomyelitis.     

MRI and diabetic foot infections

The role of magnetic resonance imaging and plain radiographs in evaluating osteomyelitis in the diabetic foot was studied. Fifty patients were prospectively examined by magnetic resonance imaging and plain radiographs to determine the extent of infection. Thirty-seven patients had positive MRI for osteomyelitis and 19 were positive with conventional radiography. Thirteen patients had negative MRI healed with short course of antibiotics. Five patients with positive MRI received four weeks' course of intravenous antibiotics with two still having persistent infection in the six weeks follow-up. Thirty-two patients underwent surgery with favorable results. Sixty-two bone specimens were obtained for histologic evaluation of osteomyelitis. In cases with histologic proof of diagnosis, magnetic resonance sensitivity was 99%, specificity was 81%, and accuracy was 94%. Thus magnetic resonance imaging was shown to have a high sensitivity, specificity, and accuracy in detecting osteomyelitis.     

The diagnostic role of gadolinium enhanced MRI in distinguishing between acute medullary bone infarct and osteomyelitis

The objective of the study was to evaluate the diagnostic utility of contrast enhanced magnetic resonance imaging (MRI) for distinguishing between acute medullary bone infarct and osteomyelitis. There were 11 patients (age 6-34 years) presented to our institution between December 1994 and February 1998 with a clinical differential diagnosis of acute bone infarct versus osteomyelitis and inconclusive radiographs were imaged using MRI. All but one received i.v. gadolinium. Nine of the patients had homozygous Sickle Cell disease (SCD) and two had Systemic Lupus Erythematosus (SLE), the latter requiring chronic methylprednisolone. Osteomyelitis was confirmed either by biopsy alone or by the combination of Gallium(67) scan in conjunction with positive blood cultures and clinical resolution following antibiotics. Infarcts without osteomyelitis were confirmed either by biopsy or resolution of symptoms without antibiotic therapy. All patients had at least six months clinical follow-up. The results found that seven of nine patients with SCD had acute infarct only. One patient with SCD had osteomyelitis only. Three patients (two SLE and one SCD) had both acute-on-chronic infarcts and superimposed osteomyelitis, one with an adjacent soft tissue abscess. Accurate distinction between infarct and osteomyelitis was impossible for one patient with SLE who did not receive contrast. All other cases were correctly diagnosed prospectively based on distinct patterns of MRI contrast enhancement. In all adult patients, acute infarcts demonstrated thin, linear rim enhancement on MRI while osteomyelitis revealed more geographic and irregular marrow enhancement. Two of four cases of osteomyelitis also demonstrated subtle cortical defects with abnormal signal traversing marrow and soft tissue. The single pediatric patient demonstrated elongated, serpiginous central medullary enhancement with periostitis. We concluded that the pattern of MR contrast enhancement may allow accurate distinction between acute infarct and osteomyelitis, or recognition of osteomyelitis superimposed on bone infarction.     

Superparamagnetic iron oxide (SPIO) as an oral contrast agent in gastrointestinal (GI) magnetic resonance imaging (MRI): Comparison with state-of-the-art computed tomography (CT)

This study was conducted to compare the sensitivity and specificity of abdominal magnetic resonance imaging using oral superparamagnetic iron oxide with oral contrast-enhanced computed tomography in the detection of GI pathology. Overall sensitivity was calculated to be 83% for OECT compared to 67% by SPIO MRI. Specificity for OECT was 68% compared to 89% for SPIO MRI. The results from imaging with superparamagnetic iron oxide and imaging with oral contrast-enhanced computed tomography were in agreement in 14 subjects who had normal gastrointestinal tracts. In the remaining 16 patients, eight pathologic entities were detected by both modalities whereas 15 abnormalities were seen by only one modality. Superparamagnetic iron oxide magnetic resonance imaging was helpful in discriminating normal bowel from solid lesions and in detecting subtle gastrointestinal tract mass effect. In 30 consecutively studied patients suspected of having GI pathology, OECT was more sensitive than SPIO MRI in detecting abdominal pathology. Conversely, SPIO MRI was more specific than OECT.     

Magnetic resonance imaging of soft-tissue tumors: Comparison with computed tomography

Twenty-seven patients with soft-tissue tumors were examined with a Picker 0.15-tesla resistive magnet and by computed tomography (CT). In all but one patient, MRI was better than or equal to CT in defining the anatomic extent of the tumor. We could determine whether major vascular structures were engulfed by the tumor in 80% of the MRI examinations but only in 62% of the CT scans. MRI and CT were equally effective in determining the presence or absence of bony invasion. The MRI images of all the tumors showed increased signal intensity relative to normal muscle when spin-echo (SE) sulse sequences with long repeat times were used (SE: echo time [TE], 60 ms; repetition time [TR], 2,000 ms). When T1 weighted pulse sequences were used (SE: TE, 30 ms; TR, 500 ms or inversion recovery: inversion time, 500 ms; TE, 40 ms; TR, 2,000 ms) the malignant tumors showed decreased signal intensity compared to normal muscle. Only lipomas showed high signal intensity on both T1 and T2 weighted pulse sequences.     

A comparison of ferumoxytol with gadolinium as contrast agents for the diagnostic magnetic resonance imaging of osteomyelitis

BackgroundFerumoxytol, an FDA-approved superparamagnetic iron oxide nanoparticle (SPION) preparation used for the treatment of iron deficiency anemia, is also known to be taken up by macrophages in areas of infection or inflammation, where it produces negative contrast changes on T2-weighted MR images.PurposeWe sought to compare Ferumoxytol-induced MRI contrast changes with those observed using standard-of-care Gadolinium in patients presenting with symptoms suggestive of osteomyelitis.SubjectsOut of eighteen enrolled patients, 15 had MR imaging with both ferumoxytol and gadolinium. Based on clinical and/or pathologic criteria, 7 patients were diagnosed with osteomyelitis, 5 patients had osteomyelitis ruled out, and in 3 patients a definitive diagnosis could not be made.Field strength1.5 Tesla.SequencesUsed included STIR, T1-weighted and T2-weighted spin echo.AssessmentThe mean contrast changes upon ferumoxytol and gadolinium administration were measured from lesion regions of interest and compared with control regions.Statistical testsStudent's t-test, propagation of errors. Data are reported as means ± S.E.ResultsThe mean contrast changes, ΔC, associated with a diagnosis of osteomyelitis were found to be ΔCFe = −2.7 ± 0.7 when Ferumoxytol and T2w imaging sequences were used and ΔCGd = +3.1 ± 1.1 (P < 0.001) when Gadolinium and a T1w imaging sequence was used. The MRI contrast changes for both agents correlated with systemic markers of inflammation, such as the erythrocyte sedimentation rate. In patients without osteomyelitis, no significant contrast changes were observed in T2-weighted, Ferumoxytol-contrasted MRI. The macrophages in osteomyelitic lesions were found to take up at least 16 times as much iron as benign bone marrow.Data conclusionWe conclude that in terms of its MRI diagnostic accuracy for osteomyelitis Ferumoxytol-contrasted MRI is a promising approach for diagnosing osteomyelitis that merits further study.     

MRI of aggressive bone lesions of childhood.

MRI can yield valuable information about involvement of bone and soft tissue by aggressive bone lesions of childhood. The 18 lesions evaluated with MRI included osteosarcoma, Ewing's sarcoma, histiocytosis, osteomyelitis, osteoblastoma, giant cell tumor, aneurysmal bone cyst, ossifying fibroma, and fibrous dysplasia. In 12 children, where CT correlation was available, MRI provided equal or more information than CT. Our study shows that MRI should be the modality of choice in the evaluation of aggressive bone lesions of childhood, after conventional radiography.     

Magnetic resonance imaging and computed tomography in Pelizaeus-Merzbacher disease

Six patients with the classical form of Pelizaeus-Merzbacher disease (PMD) were studied with computed tomography (CT) and magnetic resonance imaging (MRI) of the brain. While final diagnosis of PMD should be made on the basis of histopathologic findings in the brain, findings in this group support the fact that MRI can be used for tentative early diagnosis when computer tomographic examination is normal or nondiagnostic. All patients had MRI findings reflecting a pattern of diffuse white matter disease that can be considered characteristic in the appropriate clinical setting.     

Detection of bone metastases using diffusion weighted magnetic resonance imaging: comparison with C-methionine PET and bone scintigraphy

Purpose

We evaluated the ability of diffusion-weighted imaging (DWI) to detect bone metastasis by comparing the results obtained using this modality with those obtained using ¹¹C-methionine (MET) positron emission tomography (PET) and bone scintigraphy.

Materials and methods

This retrospective study involved 29 patients with bone metastasis. DWI was obtained using a single-shot echo planar imaging (EPI) sequence with fat suppression using a short inversion time inversion recovery sequence. The detection capabilities of DWI for bone metastases were compared with those of whole body MET PET (in 19 patients) and 99mTc-methylene diphosphonate bone scintigraphy (in 15 patients).

Results

Among the 19 patients who were diagnosed using DWI and PET, the PET identified 39 bone metastases, while the DWI identified 60 metastases out of 69 metastases revealed with conventional magnetic resonance imaging (MRI). Among the 15 patients who were diagnosed using DWI and bone scintigraphy, the bone scintigraphy identified 18 bone metastases, while the DWI identified 72 metastases out of 78 metastases revealed with conventional MRI. The overall bone metastasis detection rates were 56.5% for PET, 23.1% for bone scintigraphy and 92.3% for DWI.

Conclusion

DWI is a very sensitive method for detecting bone metastasis and is superior to MET PET and bone scintigraphy in terms of its detection capabilities.     

Evaluation of the prostate by magnetic resonance imaging

Forty-seven male patients with suspected prostatic disease underwent magnetic resonance imaging (MRI) of the pelvis on a Picker resistive magnet operating at 0.15 T; 33 had histologically proved adenocarcinoma, 12 benign prostatic hypertrophy, 1 a transitional cell carcinoma, and 1 a seminoma. Eleven normal subjects also were included in the study. The study attempted to (1) define the MRI characteristics of the normal prostate, benign prostatic hypertrophy, and prostatic adenocarcinoma, (2) evaluate various pulse sequences in imaging the prostate, and (3) compare MRI findings with clinical, pathologic, and computed tomography results. Various pulse sequences, including inversion recovery and spin-echo with short and long TE and TR, were used. MRI was sensitive in detecting intracapsular and extracapsular prostatic disease. The finding of inhomogeneous signal texture throughout the gland was a sensitive but nonspecific finding for adenocarcinoma. A focal nodule with prolonged T1 and T2 relaxation times was the most specific MRI finding for adenocarcinoma. Extracapsular spread of neoplasm was often demonstrated, and because of its superior soft-tissue contrast ability, MRI was more accurate than computed tomography in delineating extracapsular extension.     

Artifacts in magnetic resonance imaging after surgical resection of brain tumors

Background

Since the advent of magnetic resonance imaging, metal artifacts have posed an important diagnostic problem in different fields of medicine. However, this has not been systematically studied in patients undergoing surgery for brain tumors.

Objective

This study was planned to assess whether metal artifacts can occur in patients undergoing brain surgery without metallic implants.

Methods

Of 40 individuals who could be included because of having a pre- and postoperative MRI and a postoperative computed tomography (CT) scan or a conventional skull X-ray for the detection of metallic artifacts, 26 patients agreed to participate in this study and gave informed consent.

Results

Twenty-six subjects, 12 males and 14 females, with an age range of 12 to 54 years, were included in the study. Four patients were found to have gross metal particles in their postoperative brain CTs and were excluded. Of the remaining 22 subjects, 7 patients (31.8%) had metallic artifacts.

Conclusion

Our study showed that simple bone drilling or chiseling during surgical manipulation of skull bones may result in separation of very tiny metal particles which can remain in the surgical site and cause artifacts in postoperative MRIs. This finding appeared to be independent of factors such as age, sex, tumor/incision site, tumor size, pathologic tumor type, total radiation dose, operation–MRI time interval and sequence of MRI.     

Quantitative magnetic resonance imaging in consecutive patients evaluated for surgical treatment of temporal lobe epilepsy

We present the results of quantitative Magnetic Resonance Imaging (MRI) in 55 consecutively referred patients with clinical evidence of temporal lobe epilepsy (TLE). The Cavalieri method was used in combination with point counting to provide unbiased estimates of the volume of the left and right hippocampus, amygdala, temporal lobe, lateral ventricles and cerebral hemisphere, and pixel by pixel maps of the T2 relaxation time were computed for both central and anterior sections of the hippocampus. The 99th centiles of hippocampal volume, hippocampal volume asymmetry and T2 relaxation times in 20 control subjects provided limits which identified the presence of MTS. The results of the quantitative MRI were compared with the results of conventional diagnostic MRI, foramen ovale (FO) recording and the WADA test. Thirty-one patients were found to have unilateral MTS (17 left and 14 right) and 7 bilateral MTS. No evidence of MTS was detected in 16 patients. Of the 31 patients diagnosed with unilateral MTS on the basis of hippocampal volume and T2 measurement, 74% and 77% would respectively have received the same diagnosis on the basis of hippocampal volume and T2 measurements alone. In comparison to FO recording, quantitative MRI has a sensitivity of 55% and a specificity of 86%, while conventional diagnostic MRI has a sensitivity of 42% and a specificity of 80% for detection of MTS. Unilateral abnormalities were detected by FO recording in 30% cent of patients who appeared normal on quantitative MRI. WADA test results were available for 40 patients. The findings were consistent with quantitative MRI showing reduced memory function ipsilateral to unilateral MTS in 18 patients, but reduced memory function contralateral to unilateral MTS in two patients, and reduced memory function without MR abnormality in seven patients. WADA testing revealed unilateral memory impairments where MRI found bilateral pathology in 4 patients and in 4 patients in whom quantitative MRI detected unilateral MTS there was no evidence of reduced memory during WADA testing of the corresponding cerebral hemisphere. In the patients with unilateral right MTS a highly significant negative correlation (p = 0.0003) was observed between age of onset and the volume of the contralateral temporal lobe.

Quantitative MR imaging of the hippocampus (i.e. volume and T2 measurement) is preferable to conventional radiological reporting for providing objective evidence of the presence of MTS on which to base the referral of patients for surgery, and since it has associated morbidity FO recording is now only being used in selected patients. Furthermore, stereology provides a convenient method for estimating the volume of other brain structures, which is relevant to obtaining a better understanding of the effects of laterality and age of onset of TLE.     

Chest MRI of patients with COVID-19

During the pandemic of novel coronavirus infection (COVID-19), computed tomography (CT) showed its effectiveness in diagnosis of coronavirus infection. However, ionizing radiation during CT studies causes concern for patients who require dynamic observation, as well as for examination of children and young people. For this retrospective study, we included 15 suspected for COVID-19 patients who were hospitalized in April 2020, Russia. There were 4 adults with positive polymerase chain reaction (PCR) test for COVID-19. All patients underwent magnetic resonance imaging (MRI) examinations using MR-LUND PROTOCOL: Single-shot Fast Spin Echo (SSFSE), LAVA 3D and IDEAL 3D, Echo-planar imaging (EPI) diffusion-weighted imaging (DWI) and Fast Spin Echo (FSE) T2 weighted imaging (T2WI). On T2WI changes were identified in 9 (60,0%) patients, on DWI – in 5 (33,3%) patients. In 5 (33,3%) patients lesions of the parenchyma were visualized on T2WI and DWI simultaneously. At the same time, 4 (26.7%) patients had changes in lung tissue only on T2WI. (P(McNemar) = 0,125; OR = 0,00 (95%); kappa = 0,500). In those patients who had CT scan, the changes were comparable to MRI. The results showed that in case of CT is not available, it is advisable to conduct a chest MRI for patients with suspected or confirmed COVID-19. Considering that T2WI is a fluid-sensitive sequence, if imaging for the lung infiltration is required, we can recommend the abbreviated MRI protocol consisting of T2 and T1 WI. These data may be applicable for interpreting other studies, such as thoracic spine MRI, detecting signs of viral pneumonia of asymptomatic patients. MRI can detect features of viral pneumonia.     

Proton density water fraction as a biomarker of bone marrow cellularity: Validation in ex vivo spine specimens

The purpose of this study was to evaluate a magnetic resonance imaging (MRI) technique for quantifying the proton density water fraction (PDWF) as a biomarker of bone marrow cellularity. Thirty-six human bone marrow specimens from 18 donors were excised and subjected to different measurements of tissue composition: PDWF quantification using a multiple gradient echo MRI technique, three biochemical assays (triglyceride, total lipid and water content) and a histological assessment of cellularity. Results showed a strong correlation between PDWF and bone marrow cellularity from histology (r = 0.72). A strong correlation was also found between PDWF and the biochemical assay of water content (r = 0.76). These results suggest the PDWF is a predictor of bone marrow cellularity in tissues and can provide a non-invasive assessment of bone marrow changes in clinical patients undergoing radiotherapy.     

Noninvasive localization of parathyroid adenomas: a comparison of X-ray computerized tomography, ultrasound, scintigraphy and MRI

Thirty-two (32) patients with primary hyperparathyroidism (17 with prior localization surgery, 15 without) were studied by a combination of computed tomography (CT), ultrasound (US), nuclear medicine (NM), and magnetic resonance imaging (MRI) for parathyroid adenoma localization. The sensitivity and true-positive ratio of each imaging technique and various combinations of techniques were evaluated. Of the 28 proven parathyroid adenomas (27 by surgery, 1 by digital subtraction angiography), 24 were imaged by two techniques, 19 by three techniques, and 10 by all four imaging techniques. The sensitivities were NM (65%), CT (76%), US (77%), and MRI (81%). The differences between true-positive ratios of 82%, 64%, 71%, and 77%, respectively, were not statistically significant. If multiple techniques were considered as a single test (i.e., a positive localization requires two or more tests to be positive at the same location), then sensitivity for a two-study combination was 79% and true-positive ratio 86%. Three techniques showed a sensitivity of 63% and a true-positive ratio of 92%, four modalities 40% and 100%, respectively. There was no significant difference in the various combinations of techniques employed (e.g., CT and US, US and MR, NM and MR, etc.). Thus, there appears to be an advantage in performing multiple techniques (regardless of which combination is selected) until two tests are positive at the same location.     

A Comparative Study of CT and MRI for Evaluating Hepatic Malignant and Focal Nodules Based on ROC Curves

The clinical use of magnetic resonance imaging (MRI) and multiphase enhanced computed tomography (CT) with the contrast media (Gd-EOB-DTPA) for detecting hepatic malignant and focal nodules prior to operation was examined based on the receiver operating characteristic (ROC) curve. This study included 70 patients with malignant and focal liver nodules who underwent MRI and multiphase CT scans before operation. Both scans for each patient were conducted within 1 month. For MRI, the T ₂-weighted image (single shot fast spin echo) and two-dimensional (2-D) and 3-D T ₁-gradient magnetic signals were obtained for all patients before administering the contrast media. The 2-D and 3-D T ₁-gradient magnetic signals were obtained in the same location after delivering the contrast media. For the CT scans, images of artery phase, portal phase, and delayed phase were obtained at a thickness of 5 mm or less after administering contrast similar to MRI. An ROC curve was used (paired-samples T test, P < 0.05) to evaluate the images. When the analysis was based on the ROC curve, MRI showed high values (P < 0.05) for area under curve (AUC), sensitivity, and specificity in terms of detection rates of small lesions (less than 2 cm and more than 2 cm) compared to multidetector computed tomography (MDCT) (for ≤2 cm, MRI: 0.928, 70, 93%, CT: 0.775, 30, 90%; for ≥2 cm, MRI: 0.744, 80%, 84%; CT: 0.692, 40%, 84%). Gd-EOB-DTPA contrast media-enhanced MRI scanner for detecting malignant and focal liver nodules before operation showed the higher detection rate of lesion and classification of lesion as either benign or malignant than multiphase enhanced MDCT when the ROC curve was used for analysis. Based on these results, we believe that analysis based on the ROC curve will provide guidelines for evaluating malignant and focal hepatic lesions prior to operation.     

Texture analysis of multiple sclerosis: a comparative study

The difficulty of using magnetic resonance imaging (MRI) to support early diagnosis of multiple sclerosis (MS) stems from the subtle pathological changes in the central nervous system (CNS). In this study, texture analysis was performed on MR images of MS patients and normal controls and a combined set of texture features were explored in order to better discriminate tissues between MS lesions, normal appearing white matter (NAWM) and normal white matter (NWM). Features were extracted from gradient matrix, run-length (RL) matrix, gray level co-occurrence matrix (GLCM), autoregressive (AR) model and wavelet analysis, and were selected based on greatest difference between different tissue types. The results of the combined set of texture features were compared with our previous results of GLCM-based features alone. The results of this study demonstrated that (1) with the combined set of texture features, classification was perfect (100%) between MS lesions and NAWM (or NWM), less successful (88.89%) among the three tissue types and worst (58.33%) between NAWM and NWM; (2) compared with GLCM-based features, the combined set of texture features were better at discriminating MS lesions and NWM, equally good at discriminating MS lesions and NAWM and at all three tissue types, but less effective in classification between NAWM and NWM. This study suggested that texture analysis with the combined set of texture features may be equally good or more advantageous than the commonly used GLCM-based features alone in discriminating MS lesions and NWM/NAWM and in supporting early diagnosis of MS.     

Abdominal aortic aneurysm evaluation: comparison of US, CT, MRI, and angiography

We studied 26 cases of abdominal aortic aneurysm with magnetic resonance imaging (MRI), computed tomography (CT), ultrasonography (US), and angiography. Data acquired were compared to those obtained at surgery. Diameter of the aneurysm was correctly defined in all cases by CT and MRI, while angiography underestimated the diameter of lesions without peripheral calcifications. Involvement of renal arteries was present in four cases and correctly diagnosed with MRI and angiography in all of them. CT did provide this information in three cases and US were not useful. Also, iliac arteries involvement was depicted by CT, MRI, and angiography in 10 out of 10 patients. Coronal sections of MRI provided comparable images to those of angiography. By comparing these different techniques we verified the good reliability of MRI as investigation tool for an accurate evaluation of aneurysms; its only limit lying in the poor capability of detecting calcifications.     

应用MRI研究CO2在癸烷中的扩散

应用核磁共振成像(MRI)技术可视化研究CO₂在癸烷中的扩散,在MRI系统采集图像的同时,应用双室压力衰减法（PVT法）监测压力,通过对MRI图像进行信号强度分析,可得到CO₂的无量纲浓度分布,然后基于菲克定律应用有限体积法可计算得出与扩散距离和扩散时间有关的扩散系数,并可得到任意扩散时间范围内的整体平均扩散系数,MRI方法得出的扩散平衡时间范围内的整体平均扩散系数与PVT法相比较误差为2.7%,并且与相似条件下的前人实验结论具有相同的数量级(10^–9)．根据实验结果得出,扩散系数沿扩散方向下降且随时间以指数形式降低,整体平均扩散系数随扩散时间的增加而减小．     

Feasibility study of myocardial perfusion and oxygenation by noncontrast MRI: comparison with PET study in a canine model

The purpose of this study was to examine the feasibility of quantifying myocardial blood flow (MBF) and rate of myocardial oxygen consumption (MVO(2)) during pharmacologically induced stress without using a contrast agent. The former was measured by the arterial spin labeling (ASL) method and the latter was obtained by measuring the oxygen extraction fraction (OEF) with the magnetic resonance imaging (MRI) blood oxygenation level-dependent effect and Fick's law. The MRI results were compared with the established positron emission tomography (PET) methods. Six mongrel dogs with induced acute moderate left coronary artery stenosis were scanned using a clinical PET and a 1.5-T MRI system, in the same day. Regional MBF, myocardial OEF and MVO(2) were measured with both imaging modalities. Correlation coefficients (R(2)) of the three myocardial indexes (MBF, OEF and MVO(2)) between MRI and PET methods ranged from 0.70 to 0.93. Bland-Altman statistics demonstrated that the estimated precision of the limits of agreement between MRI and PET measurements varied from 18% (OEF) to 37% (MBF) and 45% (MVO(2)). The detected changes in these indexes, at rest and during dobutamine stress, were similar between two image modalities. The proposed noncontrast MRI technique is a promising method to quantitatively assess myocardial perfusion and oxygenation.