Applied Radiology

Dr. Chaljub , Dr. Walser , and Dr. Ernst are Associate Professors of Radiology, Dr. Shah is a Radiology Resident Physician, and Dr. Cesani is an Assistant Professor of Radiology in the Department of Radiology, University of Texas Medical Branch at Galveston. Dr. LaForte is an Assistant Professor of Internal Medicine in the Department of Internal Medicine, University of Texas Medical Branch at Galveston.

In 2002, radiologists face a sea of new acronyms, including DWI, HASTE, PRESS, STEAM, GRASS, MRCP, PET, and PACS. This article will define many new acronyms utilized throughout radiology and their potential usefulness will be discussed. We will identify and review major breakthroughs in technology, emphasizing magnetic resonance (MR) imaging and briefly exploring the new tools available to diagnose and treat pathology.

Since the discovery and implementation of computed axial tomography, for which Cormack and Hounsfield shared the Nobel Prize in Medicine in 1980, ^1-3 the field of radiology has gained the ability to diagnose and characterize disease processes that would have been unthinkable only 50 years ago.

The goal of this discussion is not to cover all pulse sequences by all manufacturers, but rather to limit the scope to commercially available MR scanners and equipment in which the authors have significant experience in clinical use ⁴ : GE Medical Systems, Milwaukee, WI; and Siemens Medical, Iselin, NJ.

Major new noninvasive or minimally invasive radiologic examinations and procedures will be highlighted. The authors hope that the information provided will aid radiology residents and general radiologists as a quick reference during their educational and professional pursuits.

Neuroradiology

Magnetic resonance imaging (MRI) has revolutionized imaging of the central nervous system (CNS), secondary to superb soft-tissue contrast and multiplanar capabilities. The various diagnostic pulse sequences developed sound like an alphabet soup.

FSE T2 (GE) & TSE T2 (Siemens) -- Fast-spin-echo (FSE) and turbo-spin-echo (TSE) imaging. These T2-weighted images depict cerebrospinal fluid (CSF), edema, and most pathology as bright signal in the brain and other organs.

GRASS (GE) & FLASH (Siemens)-- Gradient-recalled acquisition in the steady state (GRASS) and fast low-angle shot (FLASH). These pulse sequences are utilized for their "myelographic" effect in imaging of the spine and for depicting blood products in the CNS.

FLAIR (GE and Siemens)-- Fluid-attenuated inversion recovery. A heavily T2-weighted sequence with suppression of CSF signal, which increases conspicuity of brain lesions. ⁵

DWI (GE and Siemens)-- Diffusion-weighted imaging. A pulse sequence utilizing echoplanar imaging (EPI) that can identify acute stroke (within 3 hours) by evaluating restricted Brownian motion as the result of edema from the stroke. ⁶ Intravenous or intra-arterial thrombolytic therapy may be instituted based on the early diagnosis of ischemia.

MRA and MRV-- Magnetic resonance arteriography and magnetic resonance venography. This noninvasive evaluation of arteries and veins in the head and neck allows detection of intracerebral aneurysms of >= 3 mm, stenosis, and dural sinus thrombosis. ⁷

MRS-- Magnetic resonance spectroscopy. This noninvasive examination of the brain evaluates metabolites in normal and abnormal brain based on hydrogen content and aids in diagnosing tumor, abscess, demyelination, and other brain abnormalities. Stimulated-echo acquisition mode (STEAM) and point-resolved spectroscopy (PRESS) are the major pulse sequences utilized.

PRESS-- Point-resolved spectroscopy. This is a "single-shot" method of obtaining MRS spectral data. ⁸

fMRI-- Functional magnetic resonance imaging. fMRI evaluates eloquent regions of the brain and aids in surgical planning for "resectability."

GDC-- Guglielmi detachable coils (Target Therapeutics, Freemont, CA). These coils are used to treat intracerebral aneurysms and arterial-venous malformations in a nonsurgical fashion deployed by a minimally invasive catheterization delivery system.

Body Imaging

PET-- Positron emission tomography. This technology uses a cyclotron-produced isotope attached to glucose (fluorodeoxyglucose-18 [FDG-18]) to diagnose tumors, which have a higher metabolic rate, as well as to monitor tumor response to therapy. PET with computed tomography (CT) fusion is the next major cross-sectional imaging product on the horizon.

EBT-- Electron beam tomography. This extremely fast computed axial tomographic technique can evaluate very small structures (coronary artery calcifications) and can scan a large portion of the body rapidly.

Multidetector CT-- Multidetector helical CT with speeds as fast as 0.5 seconds per scan. Eight detectors allow 16 slices per second; the resulting images of the heart rival EBT. Scanners are excellent for CT angiography, pulmonary angiography, and virtual colonography.

HRCT-- High-resolution computed tomography. HRCT permits detailed evaluation of the anatomy of the secondary pulmonary lobules, which is an important tool for the work-up of a variety of lung diseases.

MRCP-- Magnetic resonance cholangiopancreatography. MRCP depicts the biliary tree and the pancreatic duct noninvasively without contrast injection, ⁹ replacing traditional endoscopic retrograde cholangiopancreatography (ERCP) in many instances (Figure 1).

HASTE (Siemens) & SSFSE (GE)-- Half-Fourier acquisition single-shot turbo-spin echo (HASTE) and single-shot fast-spin echo (SSFSE). HASTE and SSFSE are MR pulse sequences, used as noninvasive alternatives to excretory intravenous urograms (IVPs), permitting diagnosis of urinary tract pathology without contrast injection. ¹⁰

STIR (GE and Siemens)-- Short tau inversion recovery. This MR pulse sequence is heavily T2-weighted with fat suppression and is extremely useful in orbital, skull base, and musculoskeletal imaging to detect edema, tumor, inflammation, and infection (Figure 2).

Hysterosonogram-- Highly detailed evaluation of the endometrium by ultrasound following distension of the uterus by water introduced via catheterization. This technique is useful for identification of endometrial cancer and small polyps.

Breast Imaging

RODEO & SPECIAL (GE)-- Rotating delivery of excitation off resonance (RODEO) ¹¹ and spectral inversion at lipids (SPECIAL). These fat suppression sequences, available with the newer GE systems, are specialized sequences used for MRI of the breast for detection of breast masses, staging of breast cancer, surgical planning, and response of tumors to chemotherapy (Figure 3). MRI of the breast is also useful to detect implant rupture. ¹²

Interventional and vascular radiology

CTA/CTV-- Computed tomographic angiography/computed tomographic venography. Helical or spiral CT technology allows evaluation of the arterial or venous system in the head and neck, chest, abdomen, and pelvis. These technologies obviate invasive procedures, such as conventional arteriograms or venograms, to diagnose carotid stenosis, pulmonary embolus, abdominal aortic aneurysms and venous clots. ¹³

MRA-- Magnetic resonance angiography. MRA of the aorta and peripheral vessels can replace invasive aortography and its potentially renal toxic contrast dose (Figure 4).

TIPS-- Transjugular intrahepatic porto-hepatic systemic shunt. This procedure treats portal hypertension secondary to cirrhosis by redirecting portal venous blood flow to the hepatic veins and bypassing the liver. A metallic stent is placed by the interventional radiologist via an internal jugular vein approach. TIPS can abate life-threatening hemorrhage from esophageal varices or treat refractory ascities.

Minimally invasive treatment of malignant hepatic tumors-- Radiofrequency ablation, ethanol ablation, laser ablation, microwave ablation, cryoablation, and chemoembolization techniques are currently available to the interventional radiologist to treat malignant hepatic tumors without surgery. ¹⁴

Endovascular repair of abdominal aortic aneurysm (AAA)-- A bifurcated stent apparatus, covered with graft material, is placed within an aortic aneurysm from an endovascular approach (femoral artery cutdowns). This minimally invasive procedure has lowered morbidity and mortality when compared with the traditional open repair and allows the patient to return to home and work within a few days.

UAE -- Uterine artery embolization. A catheter is placed into both uterine arteries, and symptomatic uterine fibroids are embolized. This procedure is >80% effective in the treatment of the bleeding, pain, and pressure associated with large uterine leiomyomata. This procedure is performed by interventional radiologists and is sought by patients who do not desire or are not candidates for hysterectomy or myomectomy.

Electronic transfer

PACS-- Picture archiving and com-munication system. Image acquisition, transfer, and storage are increasingly being performed electronically. Tech-nological advances, increased speed, and decreased cost will rapidly lead to the "filmless" radiology department and to the "filmless" operating room and hospital. Access to studies and images is gaining favor via the Web.

CSR-- Computerized speech recognition. CSR is rapidly replacing traditional radiology reporting by a transcriptionist. Due to the advantages of increased accuracy, rapid turnaround time, and lower costs, ¹⁵ CSR will eventually replace most traditional transcription reporting, thereby reducing full-time employees (FTE) and operational costs.

DICOM-- Digital Imaging and Communications in Medicine. This interface was developed by the American College of Radiology (ACR), National Electrical Manufacturer's Association (NEMA), Mallinckrodt Institute of Radiology, and the Radiological Society of North America (RSNA) for transfer of radiology images and medical information between computers.

IS-- Information system. Hospital personnel with expertise in computers are responsible for helping to install, monitor, and maintain the radiology CSR systems, PACS, and radiology information system (RIS).

Nuclear medicine

Mammoscintigraphy-- A nuclear medicine study using technetium with sestamibi, which complements mammography in detecting and staging breast carcinoma. ¹⁶

Octreoscan-- Somatostatin receptor (Indium III pentetreotide radiopharmaceutical) imaging for neuroendocrine tumors. This imaging can detect tumors with APUD (amine precursor uptake decarboxylation)-producing capabilities such as carcinoids, islet cell tumors, medullary thyroid carcinomas, pheochromocytomas, paragangliomas, and small-cell lung cancer.

Prostascint-- This indium-labeled radiopharmaceutical attached to a murine monoclonal antibody is utilized to detect metastatic prostate cancer in patients who have biopsy-proven prostate cancer and are at high risk for pelvic nodal metastasis, or in patients with equivocal or suspected occult metastatic disease.

Conclusion

The advent and implementation of cross-sectional imaging has markedly advanced medical care in the last 30 years. The goals of this manuscript were to identify and describe some of the new major technological advances in diagnostic imaging equipment and interventional procedures, and define their acronyms, which are used in clinical practice. The manuscript is noninclusive for all acronyms and manufacturers; for additional information, the reader is referred to the MR abbreviations in the review article by Brown and Semelka. ⁴

Radiologists will need to keep abreast of all these new examinations and procedures to determine their cost-effectiveness, positive and negative predictive values, and their clinical usefulness. The above-described examinations, procedures, and acronyms pervade all disciplines. It is hoped that the information provided will augment the radiologists' armamentarium to guide better dialogue with ordering clinicians and improve patient care. AR