Overview of PET/CT Imaging
Positron emission tomography combined with computed tomography, often referred to as a PET/CT scan, represents a cornerstone of modern diagnostic medicine. This hybrid imaging technique seamlessly integrates two distinct technologies: PET, which detects metabolic activity at the cellular level, and CT, which provides detailed anatomical information. The result is a fused image that allows physicians to pinpoint the location and nature of diseases with remarkable precision. In clinical practice, a pet ct scan is particularly valuable in oncology, where it helps detect cancer, determine its stage, and monitor the effectiveness of treatments. It is also increasingly used in cardiology to evaluate blood flow to the heart muscle and in neurology to assess brain disorders such as Alzheimer's disease. The synergy of these two modalities creates a powerful tool, but the diagnostic yield can be further enhanced through the use of contrast agents.
The Role of Contrast Agents
Contrast agents are substances administered to a patient before or during an imaging procedure to improve the visibility of internal structures. In the context of a pet ct scan contrast, these agents help differentiate between normal and abnormal tissues, making lesions or other pathologies stand out more clearly. For the CT portion of the scan, contrast materials absorb X-rays differently than body tissues, enhancing the contrast in the images. This is crucial for distinguishing between structures that might otherwise appear similar on a non-contrast scan, such as a tumor and surrounding healthy tissue. While the PET component of the scan uses a radiotracer to show metabolic activity, the contrast agent adds a layer of anatomical detail that is essential for accurate interpretation. Without contrast, subtle abnormalities can be missed, leading to incomplete diagnoses. Therefore, understanding the types of contrast used, their benefits, and their potential risks is fundamental for both clinicians and patients undergoing this advanced imaging procedure.
Scope of the Article
This article delves into the comprehensive world of contrast agents used in PET/CT imaging. It begins by categorizing the various types of contrast media, from common iodinated solutions to emerging targeted compounds. Next, it explores the significant benefits of using contrast, particularly in improving diagnostic accuracy. Subsequently, a detailed analysis of the associated risks, including allergic reactions and kidney-related issues, is provided, along with practical strategies for risk mitigation. The article also covers essential patient preparation and screening protocols, ensuring safety and efficacy. Furthermore, it highlights the latest advances in contrast technology, including novel agents with improved safety profiles and disease-specific targeting. Finally, the techniques for administration, such as oral and intravenous routes, and the optimal timing for their use are discussed. By the end, readers will have a holistic understanding of how contrast agents enhance the petct procedure, empowering them with knowledge for informed medical decisions.
Iodinated Contrast Media
Iodinated contrast media are the most frequently used contrast agents in PET/CT imaging, primarily for the CT component of the scan. These water-soluble compounds contain iodine atoms, which effectively block or attenuate X-rays due to their high atomic number. When injected intravenously, they circulate through the bloodstream and highlight blood vessels, organs, and areas of abnormal vascularity. In oncology, this is invaluable for characterizing tumors, which often have increased blood supply. The type of iodinated contrast used can be categorized by its osmolality. High-osmolar agents were used in the past but have largely been replaced by low-osmolar and iso-osmolar options, which are associated with fewer side effects. Non-ionic iodinated contrast, such as iohexol, iopamidol, and iodixanol, are now standard due to their lower chemotoxicity and reduced risk of adverse reactions. For a pet ct scan contrast protocol, healthcare providers must select the appropriate agent based on the patient's history, kidney function, and the specific clinical question being addressed.
Unique Considerations for Iodinated Contrast in PET/CT
While iodinated contrast is standard for CT, its use in a combined petct scan requires careful consideration. The iodine in the contrast can affect the attenuation correction algorithm used to process the PET images. Since CT data is used to correct for the absorption of gamma rays in the body, high-density contrast material can cause artifacts, potentially leading to overestimation or underestimation of the radiotracer concentration. However, modern software algorithms are designed to compensate for this, minimizing the impact on diagnostic quality. Another consideration is the timing of contrast injection relative to the PET tracer uptake. The contrast administration must be synchronized to ensure optimal vascular and parenchymal enhancement during the CT acquisition, without interfering with the biological distribution of the PET tracer. This delicate balance is managed by experienced radiologists and technologists who tailor the protocol to each patient. Despite these challenges, the diagnostic benefits of using contrast far outweigh the potential technical difficulties, making it a routine practice in many high-volume imaging centers across Hong Kong.
Barium-Based Contrast
Barium-based contrast is another category used in PET/CT, but primarily for evaluating the gastrointestinal (GI) tract. Unlike iodinated contrast, which is usually injected intravenously, barium is administered orally or rectally. In a pet ct scan contrast protocol, a barium suspension is ingested by the patient before the scan to opacify the stomach, small bowel, and colon. This allows the radiologist to differentiate the bowel from adjacent organs or pathological masses. This is particularly crucial in cases of suspected abdominal cancers, such as gastric or colorectal malignancies, where the tumor might be hidden within the normal bowel loops. Barium is an inert substance that does not enter the bloodstream, making it a safer option for patients with compromised kidney function. However, it is not without risks. Barium can cause constipation, and in rare cases of bowel perforation, it can leak into the abdominal cavity, causing peritonitis. Therefore, its use is contraindicated in patients with known or suspected bowel obstruction or perforation. In modern practice, dilute barium is often used in conjunction with a negative oral contrast agent (like water) to provide better distension of the bowel walls, improving the detection of mural lesions.
Gadolinium-Based Contrast
Gadolinium-based contrast agents (GBCAs) are less common in PET/CT but can be relevant in specific clinical scenarios. GBCAs are primarily used in magnetic resonance imaging (MRI) due to their paramagnetic properties. However, they also have X-ray attenuation capabilities, though they are significantly less effective than iodine. In a pet ct scan contrast context, GBCAs might be considered for patients who have a severe allergy to iodinated contrast, although their use for CT is off-label and less common. The main concern with GBCAs is the risk of Nephrogenic Systemic Fibrosis (NSF), a serious and potentially fatal condition linked to the use of older, linear GBCAs in patients with severe renal impairment. While newer, more stable macrocyclic GBCAs have a much lower risk, their use in PET/CT is rare due to the availability of safer alternatives. For patients with compromised kidney function, a non-contrast PET/CT or an alternative imaging modality is often preferred. Despite its limited role, understanding GBCAs is important for a complete picture of available contrast options, especially when dealing with complex patient histories.
Other Emerging Contrast Agents
The field of contrast media is evolving, with several emerging agents showing promise for PET/CT. Nanoparticle-based contrast agents, for example, are being developed to provide more targeted imaging. These particles can be engineered to specifically bind to cancer cell markers, allowing for the visualization of tumors at a molecular level. Some experimental agents combine both a radiotracer for PET and a contrast agent for CT into a single molecule, creating a true theranostic platform. These agents aim to enhance the precision of the petct procedure by providing simultaneous, co-registered information about metabolic activity and anatomical structure. Another exciting area is the development of dual-energy CT contrast agents, which can be differentiated using advanced CT scanners to provide quantitative tissue characterization. Additionally, research into oral contrast agents that are more palatable and cause fewer side effects is ongoing. As these technologies mature, they are expected to revolutionize diagnostic imaging, offering safer, more specific, and more informative options for patients undergoing PET/CT scans in centers throughout Hong Kong and globally.
Improved Image Clarity and Resolution
The primary benefit of using contrast in a pet ct scan contrast protocol is the marked improvement in image clarity and resolution. Without contrast, the CT portion of the scan produces images where different soft tissues can appear similar in density. For example, a tumor in the liver might have a similar attenuation value to the surrounding healthy liver tissue, making it difficult to detect. Intravenous contrast, however, highlights the blood vessels and increases the density of well-perfused tissues, creating a clear distinction between normal and abnormal regions. This enhances the spatial resolution of the CT images, allowing the radiologist to see the precise size, shape, and margins of a lesion. This clarity is essential for accurate staging of cancers, planning for surgeries, or guiding biopsies. Furthermore, the combined PET and CT data can be more precisely aligned when the CT images are of high quality. This reduces the chance of misregistration, where a hot spot on the PET scan is incorrectly assigned to the wrong anatomical location, leading to a more confident diagnosis.
Enhanced Detection of Lesions and Abnormalities
Contrast administration directly increases the sensitivity of petct for detecting lesions and abnormalities. Many malignant tumors are hypervascular, meaning they have an increased blood supply compared to surrounding tissues. As contrast material flows through the vascular system, it accumulates in these areas, making them much more visible on the CT component. This is particularly important for detecting small metastases, which might be too small to be clearly identified on a non-contrast CT but become apparent when they enhance. For example, in patients with colorectal cancer, liver metastases are often hypodense on non-contrast scans but become clearly visible during the portal venous phase of contrast enhancement. Similarly, brain metastases, which may be subtle on a standard CT, are readily seen after contrast administration due to the breakdown of the blood-brain barrier. In Hong Kong, where the incidence of certain cancers like nasopharyngeal carcinoma is high, the use of a pet ct scan contrast is a standard protocol to ensure that even small tumor deposits are not missed, thereby improving treatment planning and patient outcomes.
Better Differentiation Between Tissues
Beyond detecting lesions, contrast agents excel at differentiating between various types of tissues. This capability is crucial for characterizing whether a lesion is benign or malignant. For instance, a hemangioma in the liver has a characteristic enhancement pattern on CT—it fills in slowly from the periphery over time—which distinguishes it from a malignant tumor. Similarly, renal cysts, which are usually simple and benign, do not enhance after contrast administration, while solid renal tumors show clear enhancement. This differentiation helps avoid unnecessary biopsies or surgical procedures. Furthermore, contrast helps in distinguishing between post-surgical changes and recurrent disease. In patients who have undergone cancer treatment, scar tissue and inflammation can appear similar to tumor recurrence on a non-contrast scan. However, with contrast, active tumor tissue typically shows enhancement, while inactive scar tissue does not. This ability to provide functional and structural information makes the petct procedure with contrast an invaluable tool for radiologists in Hong Kong, allowing them to provide a more definitive interpretation and reduce diagnostic uncertainty.
Common Side Effects
While generally safe, contrast agents can cause side effects. Common side effects are typically mild and self-limiting. For iodinated contrast, patients might experience a feeling of warmth or a metallic taste in the mouth, which lasts only a few seconds. Nausea and vomiting are also possible, though less frequent with modern low-osmolar agents. These effects are usually transient and resolve without intervention. For barium-based oral contrast, the most common side effect is constipation, which can be managed with increased fluid intake or mild laxatives. These reactions are not life-threatening but can cause discomfort. It is important to note that the risk of these common side effects is reduced with proper patient preparation, such as ensuring the patient is well-hydrated before the scan. In a busy imaging center in Hong Kong, technologists are trained to monitor patients closely and to manage these mild reactions promptly to ensure a smooth experience during the pet ct scan contrast protocol.
Allergic Reactions
Allergic reactions to contrast agents, though relatively rare, represent a more serious risk. These can range from mild skin reactions like hives and itching to severe, life-threatening anaphylactic reactions. The incidence of severe allergic reactions to non-ionic iodinated contrast is estimated to be between 0.01% and 0.04%. Symptoms can include difficulty breathing, swelling of the face and throat, a rapid drop in blood pressure, and loss of consciousness. Risk factors for these reactions include a history of previous allergic reaction to contrast, asthma, and other allergies (e.g., to shellfish or medications). It is crucial to note that having an allergy to shellfish is not a contraindication to receiving contrast, but it warrants a careful assessment. In Hong Kong, where the population is diverse, thorough allergy screening is a routine part of the pre-procedure evaluation. If a patient has a known allergy, pre-medication with corticosteroids and antihistamines is often administered. Despite these precautions, institutions must have resuscitation equipment and trained personnel available to manage any emergency that may arise during the petct scan.
Contrast-Induced Nephropathy (CIN)
Contrast-Induced Nephropathy (CIN) is a significant concern, particularly in patients with pre-existing kidney disease. CIN is defined as a decrease in renal function, typically a rise in serum creatinine by 25% or an absolute increase of 0.5 mg/dL (44.2 μmol/L), occurring within 48 hours of contrast administration. The risk is highest in patients with chronic kidney disease (CKD), diabetes, dehydration, advanced age, and those on nephrotoxic medications. While the exact incidence varies, it is relatively low in patients with normal kidney function but can be as high as 12-25% in high-risk populations. In the context of a pet ct scan contrast decision, assessing kidney function is mandatory. In Hong Kong, where the prevalence of diabetes and hypertension is high, many patients undergoing PET/CT are at increased risk. Screening for CIN typically involves checking the eGFR (estimated glomerular filtration rate). If the eGFR is below 30 mL/min/1.73 m², the use of iodinated contrast is often avoided unless the diagnostic necessity is deemed to outweigh the risk, and alternative imaging strategies are considered.
Strategies to Minimize Risks
Numerous strategies can be employed to minimize the risks associated with contrast agents. The most effective strategy is careful patient screening. A detailed medical history, including a review of allergies, kidney function, and current medications, is the first step. For patients at risk of CIN, the primary preventive measure is adequate pre-hydration, typically with intravenous normal saline or sodium bicarbonate. Patients are also often advised to withhold metformin for 48 hours after the scan to prevent lactic acidosis if kidney function worsens. For those with a history of allergic reactions, a pre-medication protocol (e.g., prednisone and diphenhydramine) is administered 12 and 2 hours before the procedure. Using the lowest possible dose of contrast and selecting iso-osmolar or low-osmolar agents further reduces the likelihood of adverse effects. In modern practice, the use of automated power injectors with pressure monitoring ensures control over the injection rate, minimizing the chance of extravasation. In institutions across Hong Kong, these protocols are strictly adhered to, ensuring the safety of patients undergoing a petct procedure. Continuous monitoring during and after the scan allows for immediate intervention if any reaction occurs.
Medical History Review
Before any PET/CT with contrast, a comprehensive review of the patient's medical history is mandatory. This review focuses on identifying risk factors for adverse reactions. The patient is asked about any prior history of allergic reactions to contrast agents, as well as allergies to food, medications, or other substances. A history of asthma or other atopic conditions is also noted, as these patients are statistically at higher risk for allergic reactions. Additionally, the history includes an assessment of the patient's renal status, looking for a diagnosis of chronic kidney disease, diabetes, or hypertension. The current medication list is reviewed, paying special attention to nephrotoxic drugs like non-steroidal anti-inflammatory drugs (NSAIDs), certain antibiotics, and diuretics. For women of childbearing age, pregnancy status is confirmed, as radiation exposure from the scan is contraindicated. This thorough evaluation is the foundation of a safe procedure. In Hong Kong, many centers use standardized questionnaires to ensure this information is collected systematically before a pet ct scan contrast is scheduled.
Kidney Function Assessment
Assessment of kidney function is a critical step in patient preparation for a petct scan using iodinated contrast. The standard test is the measurement of serum creatinine, which is then used to calculate the eGFR (estimated Glomerular Filtration Rate). This value reflects how well the kidneys are filtering waste products from the blood. Most guidelines recommend that an eGFR should be checked within 4-6 weeks prior to the scan for all patients, and more recently (within 24 hours) for high-risk patients. In Hong Kong, where there is a relatively high prevalence of renal impairment due to diabetes and hypertension, this step is never skipped. If the eGFR is above 60 mL/min/1.73 m², the patient is considered at low risk. If it is between 30-60, the patient is at moderate risk, and the benefits of contrast administration are carefully weighed. If the eGFR is below 30, the use of iodinated contrast is generally avoided unless absolutely necessary, and an alternative non-contrast scan or a different imaging modality like ultrasound or MRI is considered. This risk-stratified approach ensures that the benefits of the contrast-enhanced PET/CT outweigh the potential harm to the kidneys.
Allergy Screening
Allergy screening is an inseparable part of the preparation for any procedure involving contrast. The patient is directly questioned about any previous reactions to contrast agents, including the severity of the reaction. Patients with a history of a prior mild reaction (e.g., hives) may be managed with pre-medication, while those with a history of a severe reaction (e.g., anaphylaxis) require a more cautious approach, possibly involving alternative imaging. The screening also includes a review of other allergies, such as to medications (e.g., penicillin), foods (e.g., eggs, milk, shellfish), or environmental allergens (e.g., pollen). While food allergies do not directly increase the risk of reaction to iodinated contrast, they can indicate a higher baseline allergic tendency. Importantly, the old myth about shellfish allergy being a strong contraindication has been largely debunked; the risk is minimal, though a cautious approach is still warranted. In Hong Kong, where food allergies to seafood are common, this point is frequently clarified with patients. If an allergy is identified, a pre-medication protocol is initiated, and the imaging team is prepared to manage a potential reaction during the pet ct scan contrast procedure.
Pre-hydration Protocols
Pre-hydration is the most effective method for preventing contrast-induced nephropathy (CIN) in at-risk patients. The goal is to expand intravascular volume, decrease the viscosity of blood, and reduce the concentration of contrast in the renal tubules. The standard protocol involves the infusion of intravenous normal saline (0.9% sodium chloride) at a rate of 1 mL/kg/hour for 12 hours before and 12 hours after the procedure. In an outpatient setting, a shorter protocol is often used, such as 3 mL/kg of normal saline infused over 1 hour before the scan. Sodium bicarbonate solutions are also proposed as an alternative or adjunct, as they may reduce free radical formation in the renal tubules. However, saline remains the standard of care. For patients undergoing an emergency petct scan, a rapid fluid bolus is given immediately before the procedure. Oral hydration is also encouraged for patients who can tolerate it. In Hong Kong's humid climate, ensuring adequate hydration is particularly important. These protocols are simple, cost-effective, and have been proven to significantly reduce the incidence of CIN, making them a critical component of patient safety for all contrast-enhanced imaging.
Development of New Contrast Agents
The field of PET/CT contrast is rapidly advancing, with a strong focus on developing new agents that are safer and more informative. One exciting area is the creation of organ-specific contrast agents. For instance, liver-specific iodinated agents are being designed to be taken up by hepatocytes, allowing for better characterization of liver lesions. These agents can differentiate between benign hepatocellular nodules and malignant metastases more accurately than standard extracellular agents. Furthermore, researchers are exploring the use of 'smart' contrast agents that change their signal in response to specific biological environments, such as the acidic pH of a tumor microenvironment. This could provide real-time functional information beyond simple anatomy. Another significant advancement is the development of nanoparticle-based contrast media. These particles can carry a high payload of iodine, providing excellent X-ray attenuation. They can also be coated with ligands that target specific receptors on cancer cells, enabling molecular imaging. These new tools hold the promise of transforming a diagnostic petct procedure into a highly targeted assessment of disease biology.
Improved Safety Profiles
A major driver of innovation in contrast agent development is the desire to improve safety profiles. The latest generation of iodinated contrast media, such as iso-osmolar agents, are designed to be closer to the body's natural blood osmolality, reducing the risk of adverse hemodynamic effects and endothelial damage. These agents are associated with a lower incidence of pain at the injection site, nausea, and severe allergic reactions. In the realm of gadolinium-based contrast, the shift from linear to macrocyclic agents has dramatically reduced the risk of NSF. Research is also ongoing to develop contrast agents that are entirely non-toxic to the kidneys. For example, some novel agents are being formulated to be cleared by the liver or other organs, bypassing the kidneys entirely. This would be a game-changer for patients with severe renal impairment who currently cannot receive standard contrast. In addition, biodegradable nanoparticle systems are being tested that break down into harmless byproducts after imaging. These continuous improvements in safety ensure that the benefits of a pet ct scan contrast can be extended to a wider and more vulnerable patient population.
Targeted Contrast Agents for Specific Diseases
The future of PET/CT contrast lies in personalization and targeting. Targeted contrast agents are designed to bind specifically to biological markers associated with particular diseases. For example, an agent might be developed to target the prostate-specific membrane antigen (PSMA) for prostate cancer, or the fibroblast activation protein (FAP) for a variety of solid tumors. These agents would not only show the location of the disease but also provide quantitative information about the expression of that target, which could guide therapy selection. In PET imaging, radiotracers already do this to some extent, but combining a targeted CT contrast agent with a PET tracer could provide synergistic data. For instance, a 'dual-modality' agent could be developed that includes both a radioactive element for PET and a high-Z element for CT. This would allow for simultaneous, perfectly co-registered molecular and anatomical imaging. This level of specificity is expected to improve the accuracy of the petct scan for diagnosing and monitoring complex diseases, reducing the need for invasive biopsies and enabling earlier, more effective treatment strategies.
Oral Contrast
The administration of oral contrast is a standard technique for PET/CT scans of the abdomen and pelvis. The goal is to opacify the gastrointestinal (GI) tract, distinguishing it from adjacent organs and pathologies. Typically, patients are asked to drink a dilute solution of barium sulfate or a low-concentration iodinated contrast agent over a period of 30 to 60 minutes before the scan. Water can also be used as a negative oral contrast agent, which provides good bowel distension without increasing the density. The choice depends on the specific clinical question and the institution's protocol. Oral contrast is crucial for detecting lesions in the bowel wall, such as colorectal cancer or inflammatory bowel disease. It also helps identify extraluminal masses that might be compressing or invading the gut. For a comprehensive pet ct scan contrast protocol, the timing of oral contrast is critical. It must be given early enough to allow the agent to travel through the entire GI tract but not so early that it leaves the small bowel. Proper administration ensures optimal visualization, which is a routine practice in imaging centers across Hong Kong.
Intravenous Contrast
Intravenous (IV) contrast administration is the most common method for enhancing the CT component of a PET/CT scan. The contrast is injected through a peripheral vein, usually in the arm or hand, using a power injector. This allows for a controlled, high-flow-rate injection, which is necessary to achieve optimal vascular enhancement. The injection is typically followed by a saline flush to push the contrast into the central circulation. The timing of the CT acquisition relative to the injection is surgical. Different phases of enhancement are used based on the clinical need: arterial phase for assessing blood vessels and hypervascular tumors; portal venous phase for liver imaging; and delayed phase for characterizing certain lesions. For a petct scan, the delay is usually set to capture the portal venous phase, which provides the best general abdominal assessment. The use of high-concentration iodine (e.g., 350-370 mgI/mL) allows for lower volumes of contrast to be used, reducing the risk of CIN. The entire process is carefully managed by a team of nurses and technologists, ensuring patient comfort and safety during the injection.
Optimal Timing of Contrast Administration
Optimizing the timing of contrast administration is a complex but essential aspect of performing a high-quality pet ct scan contrast examination. The goal is to synchronize the CT acquisition with the peak enhancement of the target organ or pathology. For the standard whole-body cancer staging protocol, the CT is usually acquired 70-80 seconds after the start of IV contrast injection, which corresponds to the portal venous phase. This timing is ideal for evaluating the liver, pancreas, and other abdominal organs. However, if the clinical question is to assess a lung lesion, an earlier arterial phase might be desired. The timing also needs to account for the simultaneous PET acquisition. Since the PET data is acquired over many minutes, the CT must provide a static snapshot that accurately represents the anatomy for attenuation correction. If the contrast timing is off, the attenuation correction map might not match the tracer distribution, leading to artifacts. Advanced CT scanners have bolus-tracking software that automatically initiates scanning when the contrast reaches a predefined threshold in a target vessel (e.g., the aorta). This technology ensures optimal timing regardless of the patient's cardiac output, a significant advantage in a busy clinical setting.
Summary of Key Findings
In summary, the use of contrast agents in a petct procedure is a powerful tool that significantly enhances diagnostic capabilities. Iodinated contrast remains the workhorse, offering superior anatomical detail and improving lesion detection. While barium-based agents are essential for GI evaluation, emerging targeted agents promise even greater specificity. The benefits, including clearer images and better tissue differentiation, are substantial. However, these must be balanced against potential risks such as allergic reactions and contrast-induced nephropathy. Through meticulous patient preparation, including thorough medical history review, kidney function assessment, and allergy screening, these risks can be minimized. Pre-hydration protocols are highly effective in preventing CIN. The latest advances, including iso-osmolar agents and targeted nanoparticles, are making contrast administration safer and more informative. Finally, proper administration techniques, whether oral or intravenous, and optimal contrast timing are crucial for maximizing the diagnostic yield of the scan.
Future Directions in PET/CT Contrast Research
Looking ahead, the future of PET/CT contrast is bright, driven by innovation in material science and molecular biology. Research is focused on developing theranostic agents that combine diagnostic imaging with therapeutic capabilities. For example, a single nanoparticle could be used to image a tumor, deliver a drug, and then monitor the response to treatment. Another promising direction is the use of artificial intelligence (AI) to optimize contrast protocols. AI algorithms can analyze patient data (age, weight, renal function) in real-time to recommend the ideal contrast volume, injection rate, and scanning delay. This personalized approach would further reduce the risk of adverse events and improve image consistency. Furthermore, research into non-iodinated, non-gadolinium contrast agents, such as those based on bismuth or gold, is ongoing, aiming to completely eliminate the risks of current agents. These advances will ensure that the pet ct scan contrast continues to evolve as an indispensable tool for precision medicine, improving outcomes for patients in Hong Kong and around the world.
