Article Review: Comparison of Spect Lung Scintigraphy and Ctpa for the Diagnosis of Pulmonary Embolism

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SPECT vs. CPTA

Pulmonary embolism or PE is the sudden blockage in a lung artery by a blood clot coming from a vein in the leg (NHLBI 2009). PE can permanently damage part of the lung due to lack of blood flow into the tissue, decrease oxygen level in the blood, or damage other organs from lack of sufficient oxygen. A large clot or too many clots can cause death. PE is often a complication of deep vein thrombosis or DVT. Other causes are resting after surgery, a long trip by car or airplane, and being bedridden for a long time. Men and women are equally at risk for PE, although risk doubles every 10 years after age 60. Most common signs and symptoms are unexplained shortness of breath, breathing problems, chest pain, coughing or arrhythmia, and the symptoms of DVT. These symptoms are swelling of the leg, the vein in the leg or tenderness in the leg or discolored skin on the affected leg (NHLBI). There are at least 100,000 PE cases in the United States every year. PE ranks third among the most common causes of deaths among the hospitalized. About 30% of those with PE will die if untreated (NHLBI). A

diagnostic testing tool with minimal radiation exposure risk will help in most cases..

Diagnosis and Diagnostic Tests

Diagnosis requires the patient's medical history and physical examination for DVT and PE, predisposition and other possible causes (NHLBI 2009). The doctor checks for DVT signs and takes the blood pressure and checks the heart and lungs. The tests to take depend on the patient's condition when he arrives in the hospital, risk factors for PE, testing options and other medical conditions. These tests include ultrasound, computer tomography scanning or CT scan, lung ventilation perfusion scan, pulmonary angiography, blood tests and other tests. These other tests include echocardiogram, electrocardiogram, chest x-ray, and chest magnetic resonance imaging or MRI (NHLBI).

Most commonly used tests among patients suspected of PE are echocargiography at 26%, CT or CT angiography of the chest at 11%, cardiac perfusion at 6.9% and duplex ultrasound at 7.3% (Bhargavan et al. 2010). The most commonly used tests for those with inpatient diagnosis of PE are chest CT or Ct angiography at 49%, duplex ultrasound at 18%, echocardiography at 10.9%, and ventilation-perfusion scintigraphy at 10.9%. There are large differences in the patterns of practice among physician specialties and geographic locations (Bargavan et al.).

Treatment

Treatment for PE is the same as DVT, such as blood thinners, anticoagulants.and thrombolytics, in life-threatening conditions (NHBLI 2009). Treatment aims at stopping blood clots before they become bigger and at preventing new clots from forming (NHLBI).

CTPA

Computerized Tomographic Pulmonary Angiography or CTPA is considered the most sensitive test for the diagnosis of PE (Anderson & Barnes 2009). Negative results from multidetector CTPA study rule out the diagnosis of PE without having to exclude a DVT finding. It was introduced in the 90s as an alternative to ventilation/perfusion scanning. Its use of radionuclide imaging of the blood vessels of the lung makes it both a precise diagnostic test and a risky one. Its ionizing radiation exposes the patient to secondary malignancies. The use of CTPA is contraindicated for pregnancy, breast cancer, allergy and renal failure (Anderson & Barnes). In response to these risks, single-proton emission tomography or SPECT V/Q and modified diagnostic criteria for V/Q scan interpretation improved their diagnostic accuracy so that they are now alternatives to CTPA with a minimal exposure to radiation. In summary, CTPA may be the most reliable diagnostic text for PE, but SPECT V/Q scanning is safer and preferred by some patient groups (Anderson & Barnes).

Increased Incidence of Radiation Cancers

The American College of Radiology expressed apprehension that the increased use of CT and some nuclear medicine studies may also increase the incidence of radiation cancers (Anderson & Barnes 2009). While its radiologist members acknowledge the benefits of CTPA as a diagnostic test for PE, they also warn against radiation exposure. A

Recent study found that women patients received 12.4-31.8 mSV from a single 6-slice multidetector CTPA procedure. Radiologists estimate that this would increase the risk of breast cancer by 1.004 to 1.042 and lung cancer from 1.005 to 1.076. Patients older than 55 years old faced the risk at less than 1% while a 20-year-old woman, at a 1.7-5.5% risk of breast or lung cancer (Anderson & Barnes).

Rise in PE Incidence and Increased Use of CTPA

Two studies showed a rise in the incidence of PE in the past decade but with unchanged mortality rates (Anderson & Barnes 2009). One study demonstrated the parallel rise in the incidence and the use of CTPA. The reports explained that the increased incidence was the result of the accuracy in the early diagnosis made by CTPA (Anderson & Barnes). The popularity of CTPA made it a kind of "one-stop" center for the diagnostic and prognostic test for PE as well as DVT. Records attest to the reliability and accuracy of the test (Moores & Holley 2008). The addition of computed tomography venography of CTV enhances the capability. Many specialists believe the added radiation from CTV is worth the risk to certain patient populations. Nonetheless, the general opinion is that clinical probability, the age of the patient and the location of the patient all determine the necessity or desirability of CTV (Moores & Holley).

Comparison with SPECT

This provides several three-dimensional images and promises to improve the diagnostic accuracy of imaging for PE (Anderson & Barnes 2009). It has been compared to CTPA in a number of studies. One, which involved 83 patients, showed a 97% sensitivity of SPECT over only 86% for CTPA, 91% specificity over 98% for CTPA and diagnostic accuracy of 94% over 93%, respectively. Another study was conducted on 405 patients, who were negative for PE by a SPECT V/Q test and not treated with anticoagulants. Only 3% of them had indeterminate scan findings. A larger study on the capability of SPECT V/Q replicated earlier findings. But larger prospective multi-center studies on accuracy and outcomes are needed to determine its usefulness (Anderson & Barnes).

A prospective, observational study subjected 100 patients around 50 years old to compare SPECT and multislice CTPA (Miles et al. 2009). It found a 95% observed agreement between them. Three cases yielded positive CTPA results and negative SPECT results. CTPA results were negative and SPECT scintigraphy results were positive in one case. None of these four cases was diagnosed with PE on first clinical reporting and no anticoagulant prescriptions. All four reported good health, specifically free of thromboembolic occurrence, after 3 months of follow-up. Three cases of positive CTPA results and negative SPECT scintigraphy were diagnosed with peripheral PE. This study revealed 83% sensitivity and 98% specificity. These are encouraging results for use on older patients with pre-existing comorbidities (Miles et al.).

SPECT lung scintigraphy is more suitable when CTPA is contraindicated as in cases of allergy, critical illness, renal impairment, diabetes or proliferating breast tissue (Miles et al. 2009). It is preferable for pregnant women because of its lower radiation dose applied on proliferating breast tissue. CTPA may be more valuable for other patients as an alternative or additional diagnostic tool at 25.4% and 29%, according to two recent studies, respectively (Miles et al.).

Another prospective study compared the diagnostic ability of V/Q SPECT, V/Q SPECT with low-dose CT, and pulmonary MDCT angiography on 196 volunteer patients suspected of PE (Gutte et al. 2009). The patients were recruited from June 2006 to February 2008 at the Department of Nuclear Medicine at Rigs Hospital. Follow-up was conducted after six months. Of the total of 81 available studies for analysis, 38% were take from patients with PE. V/Q SPECT has an established 97% sensitivity and 88% specificity. With the addition of low-dose CT, the sensitivity remained at 97% but specificity went up to 100%. In comparison, perfusion SPECT with low-dose CT had a 93% sensitivity and a 51% specificity. On the other hand, MDCT angiography had 68% sensitivity and 100% specificity. The study concluded that V/Q SPECT with low-dose CT without contrast enhancement performs excellently as a diagnostic test (Gutte et al.).

Many centers presently use only pulmonary MDCT with only suboptimal results on account of possible lower sensitivity and higher radiation dose (Gutte et al. 2009). MDCT is widely used because of its constant availability, lower cost, high turnout of conclusive results and the centers' staff lack of experience with V/Q SPECT. Recently proposed algorithms omitted V/Q scintigraphy from the work-up. It is considered only an alternative when MDCT cannot be used, such as in cases of severe renal insufficiency, allergy to intravenous agents, or an inconclusive CT-based strategy. One strong point of SPECT in the study was the exclusion of 46 or 24% of the volunteer patients who had renal dysfunction. It suggested that MDCT would not be appropriate in their case (Gutte et al.).

V/Q SPECT is considered a functional technique as compared with MDCT angiography (Gutte et… [END OF PREVIEW]

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Comparison of Spect Lung Scintigraphy and Ctpa for the Diagnosis of Pulmonary Embolism.  (2011, May 12).  Retrieved December 7, 2019, from https://www.essaytown.com/subjects/paper/comparison-spect-lung-scintigraphy/755299

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"Comparison of Spect Lung Scintigraphy and Ctpa for the Diagnosis of Pulmonary Embolism."  12 May 2011.  Web.  7 December 2019. <https://www.essaytown.com/subjects/paper/comparison-spect-lung-scintigraphy/755299>.

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"Comparison of Spect Lung Scintigraphy and Ctpa for the Diagnosis of Pulmonary Embolism."  Essaytown.com.  May 12, 2011.  Accessed December 7, 2019.
https://www.essaytown.com/subjects/paper/comparison-spect-lung-scintigraphy/755299.