1、Respiratory SystemMain Contentsv Introductionv Lung Perfusion Imagingv Lung Ventilation Imagingv Clinical Applications1.IntroductionvRespiratory system consists of respiratory tract and lung.Gas exchange is the most important function of the respiratory system.vThe trachea divides into right and lef
2、t main bronchi and these in turn divide into lobar bronchi(upper,middle,and lower on the right,and upper and lower on the left).The airways continue to divide into terminal bronchioles,respiratory bronchioles,alveolar ducts and alveolar sacs.vThe pulmonary artery divides to form the right and left p
3、ulmonary arteries.These vessels follow the bronchi and bronchioles,dividing with them until they reach the alveoli.vAlveolus,totally about 250 to 300 million in lungs of an adult,is supplied by a terminal pulmonary arteriole,which has a diameter of about 35 um and which gives rise to about 1000 capi
4、llaries per alveolus.The capillaries are 7 to 10 um in diameter.The distance between the alveolar surface and the capillaries is only 0.05-0.1 um.The pulmonary capillaries drain into the pulmonary veins and from there into the left atrium.The lung also receives blood through the bronchial arteries f
5、rom the aorta.vThe radionuclide imaging of the respiratory system is mainly constituted by lung perfusion imaging and ventilation imaging.The most important application of ventilation/perfusion(V/Q)imaging is the evaluation of patients with suspected pulmonary embolism(PE).vOther applications of V/Q
6、 imaging are related to assessment of regional pulmonary ventilation and perfusion in other pathologic states,such as chronic obstructive pulmonary disease(COPD)lung cancer,pulmonary hypertension,asthma,and preoperative and postoperative evaluation of lung function.2.Lung Perfusion Imaging2.1 Princi
7、plePulmonary perfusion imaging is based on the principle of capillary blockade.Particles slightly larger than the pulmonary capillaries(8um)are injected intravenously and travel to the right heart,where venous blood is uniformly mixed.nRadiolabeled particles in the pulmonary arterial blood pass into
8、 the distal pulmonary circulation.Because the radioactive particles are larger than the capillaries,they lodge in the precapillary arterioles.Their distribution in the lung reflects the relative blood flow to pulmonary segments.nPulmonary segments with decreased or absent blood flow show diminished
9、radioactivity.2.2 Methods 2.2.1 Radiopharmaceuticalsv99mTc-labeled macroaggregated albumin(99mTc-MAA)is the most frequently used radiopharmaceutical to imaging lung perfusion.The MAA has a mean size of 40 um with a range of 10 to 90 um.vTypically,100,000 to 700,000 particles are injected to ensure r
10、eliable count statistics and image pulmonary arterial trees are temporarily and safely occluded.2.2 Methods 2.2.2 InjectionvThe usual dose of 99mTc-MAA is 3 to 5 mCi(111 to 185 MBq).vThe syringe containing the 99mTc-MAA should be gently agitated prior to injection to resuspend all particles.The 99mT
11、c-MAA is administered intravenously and should be given slowly.vThe patient is injected in supine position to minimize the pulmonary perfusion gravitational gradient.The patient should be encouraged to breathe deeply to aerate the maximum number of alveoli in the maximum number of pulmonary lobules
12、during the injection.Blood should not be drawn into the syringe because aspirated blood may form clots.vSeveral types of patients should receive a reduced number of particles for perfusion imaging.Patients with severe pulmonary hypertension and right-to-left shunts should be given only half the conv
13、entional dosage.Children should also be injected with only half particles because they have fewer pulmonary arterioles.To perform reduced-count imaging,the acquisition time for each perfusion view should be longer,allowing for nearly equivalent count statistics.2.2 Methods 2.2.3 AcquisitionvPlanar a
14、cquisition:Once the injection is complete,image acquisition can begin immediately.The patient is usually imaged in the supine position using a large field of view gamma camera or SPECT with a low-energy,all-purpose parallel-hole collimator.vImages are obtained in the anterior,posterior,right lateral
15、,left lateral,right posterior oblique,left posterior oblique,right anterior oblique,and left anterior oblique positions.500,000 counts per image are recommended.2.2 Methods 2.2.3 AcquisitionvSPECT acquisition:The patient remains in supine position using a large field of view dual-head gamma camera o
16、r SPECT with a low-energy,all-purpose parallel-hole collimator.A 360 SPECT acquisition in 32 steps of 30 s each of the pulmonary perfusion is performed using a 128128 matrix with a 1.6 zoom.For the double-head camera,a 180 rotation per head was done.Accordingly,the total acquisition time per SPECT t
17、urn was 16 min.By imaging reconstruction,the transverse,coronal,and sagittal slices are obtained in a slice thickness of 3-6 mm.2.3 Normal Images vThe normal perfusion planar and SPECT images show uniform distribution of radioactivity outlining the lung fields with only a slight preference for depos
18、ition of MAA particles towards the base of the lungs.The heart causes a smoothly defined defect along the left medial lung border that is curvilinear in all projections.The hilar structures are frequently perceived as photogenic areas corresponding to the large airway and vascular structure in the h
19、ilum.vThe spine and sternum effectively attenuate activity in the midline,resulting in a separation of the left and right lungs.Uptake in the thyroid and stomach typically indicates free pertechnetate and uptake in the liver indicates colloidal impurities.Normal perfusion planar imagesT h e t r a c
20、e r i s n o r m a l l y distributed evenly throughout the lung.There is somewhat sparseness at the apices.The cardiac impression may be seen on anterior and left lateral view.Normal lung perfusion imagingPulmonary segments1.Apical segment2.Posterior segment3.Anterior segment4.Upper segment5.Inferior
21、 segment6.Lateral segment 7.Medialsegment8.Dorsal segment9.Medial basal segment10.anterior basal segment 11.lateral basal segment 12.posterior basal segment Superior lobemiddle lobe of left lungmiddle lobe of right lungInferior lobe2.3 Abnormal Images vFocal defects or reduced tracer distribution co
22、uld be caused by the pulmonary arteries stenosis,occlusion and embolism,which are resulted from various diseases.Perfusion defects can be divided into segmental and nonsegmental in nature.Defects caused by blockage of the pulmonary arterial tree should reflect the branching or arborization of the pu
23、lmonary circulation in its classic segmental pattern.vThus a classic segmental defect corresponding to one or more bronchopulmonary segments)is wedge-shaped and pleural-based.The nonsegmental defects refer to abnormalities that do not correspond to the pulmonary segments,are not pleural-based,and do
24、 not have the classic wedge shape.Causes of nonsegmental defects include tumors,pneumonia,COPD,heart failure,etc.NormalPatient with pulmonary embolism 3.Lung Ventilation Imaging3.1 PrincipleThe radioactive gas or aerosol in the closed system can be inhaled by respiratory passage,and deposit on the l
25、ining of the bronchoalveolar spaces.The distribution of radioactivity within the lungs is proportional to regional ventilation.So regional airway patency and ventilation function can be assessed through camera or SPECT detecting the radioactivity distribution of lungs.3.2 Methods vPharmaceuticals us
26、ed in ventilation imaging can be divided into two groups on the basis of their various physical forms;radioactive gas,and aerosols.The most commonly used radioactive gases are Xenon-133(133Xe),but aerosol imaging is by far the most usual technique for ventilation imaging.3.2 Methods 3.2.1 Radioaeros
27、ol imagingvCurrently,the most commonly used radioaerosol is Tc-diethylenetriaminepentaacetic acid(99mTc-DTPA).vThe other particular aeroaol is Technegas,regarded as a pseudogas because of its very small particle size,giving aerodynamic properties simulating a gas.v99mTc-DTPA:A dose of approximately
28、30 to 40 mCi of 99mTc-DTPA is introduced into the commercially available nebulizer,which generates respirable aerosol particles.vTechnegas:Because of the problem with central airway deposition of Tc-DTPA radioaerosol,the newer agent,Technegas has been developed.It is formed by burning Tc-pertechneta
29、te in a carbon crucible at very high temperatures(2500 IC)which produces an ultrafine radiolabeled aerosol(particle size 2 to 20 nm).vPlanar acquisition:Standard projections for both 99mTc-DTPA aerosol and Technegas ventilation scans are anterior,posterior,right posterior oblique,left posterior obli
30、que,right lateral,left lateral,and preferably right anterior oblique and left anterior oblique,corresponding to the perfusion scan.vSPECT acquisition:(see 2.2.3)Normal radioaerosol imaging3.2 Methods 3.2.2 Xenon-133(133Xe)imagingv133Xe is a radioisotope widely used to perform ventilation lung scans
31、overseas.A noble gas produced by fission of uranium-235 in a nuclear reactor;133Xe has a half-life of 5.3 days and decays by beta and gamma radiation.The photon energy is 81 keV.vThe 133Xe ventilation scan consists of three consecutive phases of a single-breath,an equilibrium and a washout phase.A l
32、arge field of view gamma camera or SPECT with a tow-energy,all-purpose,parallel-hole collimator is used.The usual adult dose of 133Xe is 15 to 20 mCi.The washout phase is the most sensitive phase of the ventilation scan for the detection of airway disease.(1)Single breath phase:involves having the p
33、atient exhale as deeply as possible and then inhale 370 to 740 MBq of 133Xe,holding his or her breath for about 15 seconds while a static image is taken.(2)Equilibrium phase:which constitutes the rebreathing of the expired xenon diluted by about 2 L of oxygen contained in a closed system.The patient
34、 usually rebreathes this mixture for 2 to 5 minutes while a static image is taken.Thus the 133Xe image obtained at equilibrium essentially represents the distribution of aerated lung volume.(3)Washout phase:after equilibrium is reached,fresh air is then breathed,while serial 15 second images obtaine
35、d for 2 to 3 minutes as the Xenon clears from the lungs.In patients with chronic obstructive pulmonary disease(COPD),the washout phase may be prolonged to 3 to 5 minutes if necessary to assess areas of regional airway trapping.Assessing the probability of acute or chronic pulmonary thromboembolic di
36、sease;establishing the presence of chronic,unresolved pulmonary emboli.Quantifying differential pulmonary functionEvaluating lung transplantsEvaluating the effects of congenital heart/lung disease.Confirming the presence of bronchopleural fistulae.Evaluating the effects of chronic pulmonary parenchy
37、mal disorders such as cystic fibrosis.Clinical Indications4.Clinical ApplicationsV/Q ScanvA ventilation/perfusion lung scan,also called a V/Q lung scan,is a type of medical imaging using scintigraphy and medical isotopes to evaluate the circulation of air and blood within a patients lungs,in order t
38、o determine the ventilation/perfusion ratio.4.1 Pulmonary Thromboembolism(PE)vPulmonary embolism(PE)is a frequently occurring,acute,and potentially fatal condition in which treatment is highly effective and improves patient survival.The diagnosis of acute PE requires an interdisciplinary team approa
39、ch and may be difficult because of nonspecific clinical,laboratory and radiographic findings.vThe incidence of venous thromboembolism is approximately 1 in 1,000 per year.Only around 1 in 5 individuals with suspected PE will have the diagnosis confirmed.Approximately 10%of patients with PE die withi
40、n one hour of the attack.For those patients who survive beyond the first hour of onset,treatment with heparin or thrombolytic agents could be effective therapies.The mortality from untreated PE is on the order of 30%.vThis mortality is reduced to 3%to 10%by the appropriate anticoagulant therapy.Alth
41、ough anticoagulant therapy is effective in treating PE and reducing mortality,it is not without risk.The prevalence of major hemorrhagic complications has been reported to be as high as 10%-15%among patients receiving anticoagulant therapy.Therefore,the accurate and prompt diagnosis of PE is mandato
42、ry to reduce PE-related morbidity and mortality on the one hand,and to prevent unnecessary anticoagulant treatment on the other.V/Q scan interpretation criteria for PEThe most important application of V/Q scan is the evaluation of patients with suspected PE.The most comprehensive prospective study a
43、ddressing the role of V/Q scan in the diagnosis of PE has been the prospective investigation of the pulmonary embolism diagnosis(PIOPED)study,a multi-institutional study designed to evaluate the efficacy of various conventional methods for diagnosing acute PE.Ventilation-normalPerfusion -defectunmat
44、chDiagnosis of PEvVentilation and perfusion to broncho-pulmonary segments are matched in a healthy individual.In pulmonary embolic disease,segmental reduction in perfusion occurs with maintenance of normal ventilation.This leads to the mismatch of perfusion and ventilation in the broncho-pulmonary s
45、egment.vPulmonary embolism typically causes multiple,wedgeshaped,and bilateral perfusion defects.Perfusion lung scintigraphy has an extremely high sensitivity in the diagnosis of pulmonary embolism since a normal lung scan virtually excludes the diagnosis.vThe accuracy of a high probability V/Q scan
46、 interpretation for PE was more than 80%,that of a intermediate probability was 20%-80%,that of a low probability was 10%-20%,and that of a very low probability was less than 10%.High probability Intermediate probability Low probability Pulmonary embolism curative effectpriortreatmentposttreatment4.
47、2 Chronic Obstructive Pulmonary Disease(COPD)vThe narrowed airways associated with COPD reduce ventilation.Ventilation imaging provides one of the most sensitive ways of detecting airways damage.Lung perfusion images are also frequently abnormal.Localized hypoxia in the lung induces localized vasoco
48、nstriction.Destruction of lung tissue and inflammatory narrowing of blood vessels produce areas of reduced perfusion.vThe ventilation and perfusion abnormalities caused by COPD are different from the abnormalities expected with PE.Regions of the lung that demonstrate obstructive changes on the venti
49、lation scan usually have corresponding abnormalities on the perfusion scan in COPD.Large,widespread and diffused perfusion and ventilation abnormalities do not follow the segmental anatomy of the lung.In general,both lungs tend to be affected to a similar,though rarely identical,degree.vIn COPD pati
50、ent,the classic pattern on V/Q images is multiple matched ventilation and perfusion defects.Severe COPD can form bulla.Patients with bulla also show considerable changes in both ventilation and blood flow.V/Q images demonstrate matched,lobar defects.Perfusion imaging of COPD Ventilation imaging of C
